Thèses : « Mantle fluids »

1

Frost, Daniel James. « The properties of C-O-H fluids under upper mantle conditions ». Thesis, University of Bristol, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.295063.

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2

REMIGI, SAMANTHA. « On the application of Raman micro-spectroscopy to the characterization of Earth's CO2 fluids ». Doctoral thesis, Università degli Studi di Milano-Bicocca, 2021. http://hdl.handle.net/10281/325898.

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Questa tesi indaga l'applicabilità della micro-spettroscopia Raman per migliorare la caratterizzazione dei fluidi a CO2 terrestri, intrappolati come inclusioni fluide (FI) nelle peridotiti. Nello spettro Raman della CO2, la distanza delle due vibrazioni fondamentali è densità (d) dipendente, inoltre sono visibili le vibrazioni 13CO2 e 12CO2. Ciò permette alla micro-spettroscopia Raman di avere il potenziale per caratterizzare in situ FI a CO2, consentendo di comprendere meglio i meccanismi di trasporto del C all'interno della Terra. La proporzionalità tra le aree 13CO2 e 12CO2 con la loro concentrazione molare permette di calcolare il δ13CCO2 tramite micro-spettroscopia Raman. I rapporti delle aree richiedono precisione sulla 4° decimale per dare valori di δ13CCO2 rappresentativi dei serbatoi naturali terrestri. Gli spettri Raman sono influenzati da inevitabili effetti casuali che riducono la precisione dell'area. 42 FI a CO2 pura di alta d, provenienti dalla regione del Lago Tana e da El Hierro, sono state analizzate. Per ogni FI sono state acquisite due serie di spettri con tempi di acquisizione diversi. Di 84 serie di analisi, 23 avevano rapporti di area 13CO2/12CO2 diversi tra loro di più di un ordine di grandezza. Questi sono stati rimossi dal dataset. Il 95% dei restanti 61 set aveva riproducibilità dei rapporti di area <≈4‰, consentendo di calcolare valori di δ13CCO2 con precisione <±≈2‰. Solo poche analisi erano caratterizzate da una minore precisione. I valori di δ13CCO2 calcolati per FI nelle peridotiti dalla regione del Lago Tana hanno mostrato un’origine di mantello per la CO2, mentre quelli nelle peridotiti di El Hierro dai valori tipici di mantello. L'accuratezza delle misure è stata verificata tramite spettrometria di massa. Questa ha dimostrato che i valori di δ13CCO2 calcolati erano accurati, e consentivano di modellare la variazione isotopica a scala minerale. L’applicabilità della micro-spettroscopia Raman come densimetro per i fluidi a CO2 è stata precedentemente studiata. Molte equazioni di densimetro calcolano d differenti per gli stessi Δ, con distribuzione grafica bimodale, la cui origine non è stata ben compresa. L'origine di questa distribuzione è stata studiata nel presente lavoro calcolando la d di 40 FI a CO2 pura, provenienti da El Hierro, mediante microtermometria. I Δ sono stati misurati acquisendo spettri Raman con una procedura simile a quella adottata per altri densimetri, con risoluzione spettrale per px ≈1,50 cm-1/px. La distribuzione dei dati Δ-d è stata fittata al meglio con un'equazione polinomiale di III°, permettendo di calcolare le d della CO2 con un errore di ±0.015 g/cm3. L’equazione plottava con quelle ottenute mediante una risoluzione spettrale per px simile. Gli intervalli di confidenza al 95% della distribuzione Δ-d per tutte le equazioni sono stati calcolati mediante un algoritmo statistico. I CI hanno permesso di valutare l'accuratezza dei valori Δ-d e di definire un punto di cut-off al di sotto del quale la potenza di stima della d era bassa. Per tutti i densimetri, il punto di cut-off corrispondeva al punto in cui le distanze relative dei CI erano <7.5% (coincidenti con CO2 gassosa a P-T ambiente). Il confronto tra CI al 95% delle equazioni a bassa ed alta risoluzione spettrale per px ha mostrato che densimetri con risoluzione calcolano d statisticamente equivalente con una confidenza del 95%. Al contrario, densimetri con risoluzione diversa calcolano d non confrontabili. I risultati ottenuti hanno consentito di proporre un metodo preliminare per calcolare in situ i δ13CCO2 con una precisione ≈±2% per il 95% delle analisi. Inoltre, questi hanno migliorato la conoscenza della distribuzione Δ-d dei densimetri Raman, indicando che d di CO2 calcolate per mezzo di equazioni con risoluzione spettrale simile sono statisticamente equivalenti al 95% di confidenza per FI aventi d vicino e al di sopra del punto critico di CO2.
This thesis investigates the applicability of Raman micro-spectroscopy for CO2 density (d) and δ13CCO2 values calculations to improve characterisation of CO2 Earth’s fluid trapped as fluid inclusions (FI) in peridotites. Based on the properties of CO2 Raman spectrum, where the distance of two main vibrations is d-dependent and 13CO2 and 12CO2 vibrations are present, Raman micro-spectroscopy has the potential to become a complementary technique for in situ characterisation of CO2 FI, allowing to better understand the C transport mechanisms within Earth. The calculation of CCO2 isotopic composition by mean of Raman micro-spectroscopy is possible due to the proportionality between 13CO2 and 12CO2 areas with their molar concentration. Calculation of area ratios requires precision at 4th decimal place to obtain δ13CCO2 values representative of Earth’s natural reservoirs. Raman spectra are affected by unavoidable random effects that reduce area measurements’ precision. 42 high-d CO2-pure FI from Lake Tana region and El Hierro have been analysed. For each inclusion, two sets of spectra have been acquired by mean of different acquisition times. Among the 84 set of measurements, 23 were characterised by 13CO2/12CO2 area ratios differing more than one order of magnitude one another. These have been removed from dataset. 95% of remaining 61 sets were characterised by area ratios reproducibility <≈4‰, allowing to calculate FI δ13CCO2 values with precision <±≈2‰. Only few analyses were characterised by lower precision. Calculated δ13CCO2 values for FI trapped in peridotites from Lake Tana region showed CO2 mantle origin, while for those in peridotites from El Hierro differed from mantle isotopic signature. Accuracy of measurement has been checked by bulk measurements, proving that calculated δ13CCO2 values were accurate, and allowing to model δ13CCO2 variations at single mineral scale. The adoption of Raman micro-spectroscopy for calculating CO2 fluid d has been previously investigated. Many densimeter equations calculate different d for the same Δ values, with a bimodal graphic distribution, whose origin was not well understood. The origin of this distribution has been investigated in present work by calculating the d of 40 CO2-pure FI trapped in mantle xenoliths from El Hierro by mean of microthermometry. CO2 FI Δ values have been measured by acquiring Raman spectra applying analytical parameters common to those adopted for other densimeter equations, with spectral per px resolution ≈1.50 cm-1/px. A 3rd order polynomial equation best fitted obtained Δ-d data distribution. Equation calculates CO2 d with an error of ±0.015 g/cm3, and plots with those obtained by mean of a similar spectral per px resolution. The 95% confidence interval (CI) of Δ-d distribution for all the equations has been calculated by a bootstrapping statistical algorithm. CIs allowed to assess the accuracy of measured Δ-d values and define a cut-off point below which the CO2 d estimation power is low. For all the densimeters, cut-off point has been set where the relative distances of computed CIs were <7.5%, which corresponded for all the equations to gas-like CO2 at ambient conditions. The comparison of 95% CIs calculated for high and low spectral resolution per px equations showed that densimeters with similar spectral per px resolution calculate statistically equivalent CO2 d at 95% confidence. In contrast, densimeters with different resolution calculate incomparable CO2 d.Obtained results allowed to preliminarily propose an analytical procedure to calculate in situ δ13CCO2 with a precision of ≈±2% for 95% of the analyses. Moreover, these improved the knowledge about Δ-d distribution of Raman densimeters, indicating that CO2 d calculated by mean of equations having similar spectral resolution are statistically equivalent at 95% confidence for CO2 FI having d values near and above the CO2 critical point.

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3

Tiraboschi, C. « COH FLUIDS AT UPPER-MANTLE CONDITIONS : AN EXPERIMENTAL STUDY ON VOLATILE SPECIATION AND MINERAL SOLUBILITY IN THE MS+COH SYSTEM ». Doctoral thesis, Università degli Studi di Milano, 2015. http://hdl.handle.net/2434/260613.

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COH fluids play a fundamental role in many geological processes, controlling the location of melting in subduction zones and promoting mass transfer from the subducting lithosphere to the overlying mantle wedge. The properties of COH fluids are strictly dependent on the composition of the fluid in subduction systems, i.e., the speciation of the volatile components of the fluid itself and the presence of solutes deriving from the dissolution of rock-forming minerals. In the scientific literature, the speciation of COH fluids has been generally determined through thermodynamic calculations using equations of state of simple H2O–non-polar gas systems (e.g., H2O–CO2–CH4), equations that do not consider the complexity related to dissolution processes, which are substantially unexplored in COH fluids and limited so far to aqueous fluids (Newton & Manning, 2002). The aim of this work is to experimentally investigate the speciation of COH volatile components of the fluid and the dissolution of mantle minerals in carbon-saturated COH fluids at buffered fO2 conditions. Our experimental approach relies on two different techniques: i) analysis by means of quadrupole mass spectrometer (QMS) of the COH fluid from pierced run capsules to retrieve speciation of volatile components and ii) analysis of frozen COH fluid with laser-ablation inductively coupled plasma-mass spectrometry (LA-ICP-MS) to measure the amount of solutes. Experiments were conducted at P = 1–3 GPa and T = 700–1200 °C using a rocking piston-cylinder apparatus. Mantle minerals in equilibrium with COH fluids are represented by synthetic forsterite, enstatite and natural magnesite. fO2 conditions were controlled employing the double capsule technique and nickel–nickel oxide (NNO) buffer. We also performed a series of experimental runs in the COH-only system in single or double capsules, varying the packing material that surrounds the capsule and the oxygen buffer, to evaluate the differences in COH volatile speciation determined by the choice of the experimental setup. Quantitative analyses of COH volatile speciation were retrieved by piercing the capsule in a gas-tight vessel at T = 80 °C and convoying evolved gases to a QMS through a heated line to avoid the condensation of water. Our experimental results on COH volatile speciation highlighted the importance of the experimental verification of volatile speciation, which can diverge considerably compared to the thermodynamic model (Perplex; Connolly, 1990) depending on the experimental strategies adopted. In particular, when single capsules are employed, the packing material that surrounds the capsule exerts a major control on the COH volatile speciation. Double capsule experiments provided similar COH volatile speciation compared to thermodynamic modeling for what concerned the COH-only system. However, the addition of mantle minerals in the experimental charge at the same P–T–fH2 conditions determines a shift in the COH fluid composition toward more CO2-rich terms. At P = 1 GPa, data show an increase in CO2 of + 11 mol% at T = 800 °C and of + 26 mol% at T = 900 °C in the COH fluid in equilibrium with forsterite + enstatite compared to a pure COH fluid. To evaluate if this shift could be determined by interactions of the COH fluid with solid phases, we retrieved the solubility of mantle minerals in COH fluids through the cryogenic LA-ICP-MS technique described by Kessel et al. (2004). With this method the COH fluid is trapped into a diamond layer, the aqueous part of the COH fluid is frozen to avoid any precipitation of solutes and is analyzed through LA-ICP-MS. Experimental results on mantle minerals solubility in COH fluids suggest that the amount of dissolved material in COH fluids is similar compared to mantle mineral solubility in H2O-only fluid and ranges from the 2 wt.%, expressed as MgO + SiO2, at P = 1 GPa and T = 800 °C, to 12 wt.% at P = 2 GPa and T = 1100 °C for the forsterite + enstatite assemblage. The formation of dissolved species containing carbon, such as CO32- and Mg(HCO3)+ lead to an increase in the amount of carbon in the fluid, but not in CO2 species. In order to get the increase of CO2 that we observed in experiments analyzed through quadrupole mass spectrometry, we suggest a series of possible dissolution reactions involving Mg-solutes, which could lead to increase the amount of CO2 in the fluid. As a consequence, the quantity of CO2 infiltrating into the mantle-wedge could be remarkably high, compared to the COH fluid composition predicted by thermodynamic modeling.

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Amann, Méderic. « Evolution du magmatisme et du métasomatisme dans une marge passive pauvre en magma durant l'initiation de l'accrétion océanique : exemple de la marge fossile de la Platta (Alpes suisses) et comparaison avec le système actuel Ibérie-Terre Neuve ». Thesis, Strasbourg, 2017. http://www.theses.fr/2017STRAH014/document.

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Les parties distales des marges passives pauvres en magma représentent la transition complexe entre les domaines continentaux et océaniques. Ces zones encore peu étudiées sont pourtant des endroits clefs pour comprendre les processus impliqués durant les premiers stades de l’accrétion océanique, et plus particulièrement ceux du magmatisme et du métasomatisme. Durant ces premiers stades, ces deux processus sont gouvernés par l’exhumation mantellique. L’interaction entre les liquides magmatiques, les roches du manteau et les fluides marins vont affecter le régime thermique de la marge. De par le monde, seulement deux Transitions Océan-Continent (TOC) ont pu bénéficier d’investigations scientifiques poussées et constituent naturellement les deux sites d’études de cette thèse, à savoir, les marges actuelles conjuguées d’Ibérie-Terre Neuve du sud de l’Atlantique Nord ainsi que les marges fossiles de la Platta et de Tasna, fragments de TOCs de la Téthys Alpine Jurassique. En combinant les études de terrain ainsi que les investigations minéralogiques, pétrologiques et géochimiques, nous avons pu contraindre trois processus clefs se déroulant dans les TOCs. (i) La percolation de liquide magmatique imprégnant le manteau sous-continental hérité dans les marges Ibérie-Terre Neuve permet une refertilisation de ces marges distales. (ii) La transition géochimique visible entre les basaltes des TOCs et les basaltes de dorsales océaniques peut s’appréhender par la fusion partielle du manteau sous-continental refertilisé. (iii) Le rôle des fluides hydrothermaux, ayant des températures comprises entre 60°C et 190°C, joue un rôle sur le métasomatisme de la lithosphère en produisant une intense serpentinisation et rodingitisation, respectivement du manteau sous-continental en exhumation et des dykes basaltiques. Ces températures étant cohérentes avec une exhumation mantellique au niveau du plancher océanique
Distal parts of magma-poor rifted margins represent a complex transition between continental and oceanic domains. These areas remain poorly understood while being a key-place to unravel magmatic and metasomatic processes involved during the first stages of oceanization. At this time, these processes are enhanced by mantle exhumation, and the interaction between melts, mantle rocks and fluids affect the thermal regime of the margin. So far, only two Ocean-Continent Transitions (OCT) have been particularly investigated, namely the present-day Iberia Newfoundland conjugate margins and the fossil analog Platta-Tasna nappes, remnants of the Jurassic Alpine-Tethys OCTs. Studies presented in this Ph.D. thesis have been focused on these two margins. Here, by combining field-works, petrological, mineralogical and geochemical investigations, we have unraveled in OCTs three key-points: (i) The deep porous-flow melt percolation impregnating the long-lived inherited subcontinental mantle in Iberia-Newfoundland margins allow the refertilization of these distal domains; (ii) The geochemical transition depicted from OCT-basalts towards MOR-basalts can be explained by the partial melting of the refertilized subcontinental mantle; (iii) The role of active hydrothermal fluids, on both the exhumed mantle and basalt dikes, lead to the serpentinisation and the rodingitization respectively, at temperature ranging between 60°C and 190°C. These temperatures being consistent with the ongoing mantle exhumation towards near-seafloor conditions

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Davies, Nigel Howard. « Numerical representations of fluid mixing ». Thesis, University of South Wales, 1993. https://pure.southwales.ac.uk/en/studentthesis/numerical-representations-of-fluid-mixing(3bf1cb31-ec80-49f2-95ae-a2f56eeeeec2).html.

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The work contained within this thesis is concerned with a theoretical investigatiop of both laminar and thermally driven types of cavity flow, together with an analysis of their associated mixing processes which find applications to Industrial mixing and also to the environment. The mixing efficiency has been viewed from two perspectives namely the tracking of a selection of fluid particles, and also the simulation of the dispersive mixing of a coloured fluid element as carried along by the flow. This thesis also incorporates features of both Newtonian and a wide range of non-Newtonian fluids.

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Freeman, Jonathan. « Mantle-melt and mantle-fluid interactions in suprasubduction zones : evidence from the Troodos Massif, Cyprus ». Thesis, Durham University, 1996. http://etheses.dur.ac.uk/1220/.

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The Troodos Massif exposes an intact section of harzburgitic mantle from its contact with crustal lithologies to a depth of approximately 3 km, where it is faulted out against a mass of heavily fractured and serpentinised peridotites: the serpentinite diapir. The harzburgites are host to several generations of pyroxenitic and dunitic intrusives, many of which have features suggestive of a reaction relationship with the enclosing harzburgites such as resorbed harzburgite xenoliths and marginal dunites. Mineral chemistry and whole-rock data suggest that the harzburgites in the Troodos sequence are residues from up to 30% fractional partial melting in the spinel stability field. The serpentinite diapir exposes iherzolitic lithologies which can be modelled by 10 to 15% fractional partial melting in the spinel stability field. In both cases, the starting composition for the melt modelling was a fertile MORB mantle source. Deviations from the compositions expected to result from simple fractional partial melting are found in several situations in the mantle section and suggest that melts/fluids interacted with the mantle during and after the partial melting event. Three main situations are identified: i) enrichments in mineral chemistry and whole-rock parameters in specific parts of the background harzburgite section; ii) mineral chemistry enrichments around pyroxenites and iii) the clinopyroxene crystals in the Troodos harzburgites which have LREE/HREE ratios higher than those that could be produced by simple fractional melting models. In the background harzburgites, mineral chemistries were enriched at the top of the sequence (Anomaly 1) and in a layer towards the base of the sequence (Anomaly 2). Pyroxenites also enriched their wallrocks and two trends were identified on the basis of spinel compositions. The Type I trend is of Cr-Fe-Ti enrichment and is similar to the mineral chemistry variations in the Anomaly 1 harzburgites. The melt involved is inferred to be tholeiitic. The Type II trend is of Mg-Al enrichment and is similar to the mineral chemistry variations in the Anomaly 2 harzburgites. The melt involved is inferred to be boninitic. The fact that the lower pillow lavas (LPL) have tholeiitic chemistries and the upper pillow lavas (UPL) boninitic chemistries suggests a link between the melt which crystallised the pyroxenites and the pillow lava sequence. The clinopyroxene trace element patterns from the background harzburgites suggest that the LREE, Nd, Sr and Zr are enriched in these minerals compared to the expected values for fractional melting. The enriched component was modelled from the clinopyroxene data and is similar in trace element pattern to the enriched component in the UPL. This suggests that the addition of the subduction component that has been proposed to explain the UPL chemistries was probably added to the mantle both during and after the melting event which produced the UPL.

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Wiersberg, Thomas. « Edelgase als Tracer für Wechselwirkungen von Krusten- und Mantelfluiden mit diamantführenden Gesteinen des östlichen Baltischen Schildes ». Phd thesis, Universität Potsdam, 2001. http://opus.kobv.de/ubp/volltexte/2005/27/.

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In der vorliegenden Arbeit werden anhand der Edelgaszusammensetzung von Kimberliten und Lamproiten sowie ihrer gesteinsbildenden Minerale die Wechselwirkungen dieser Gesteine mit Fluiden diskutiert. Die untersuchten Proben stammen vom östlichen Baltischen Schild, vom Kola-Kraton (Poria Guba und Kandalaksha) und vom karelischen Kraton (Kostamuksha). Edelgasanalysen nach thermischer oder mechanischer Gasextraktion von 23 Gesamtgesteinsproben und 15 Mineralseparaten ergeben folgendes Bild: Helium- und Neon-Isotopendaten der Fluideinschlüsse von Lamproiten aus Kostamuksha lassen auf den Einfluss einer fluiden Phase krustaler Herkunft schliessen. Diese Wechselwirkungen fanden wahrscheinlich schon während des Magmenaufstiegs statt, denn spätere Einflüsse krustaler Fluide auf die Lamproite und ihr Nebengestein (Quarzit) sind gering, wie anhand der C/³⁶Ar-Zusammensetzung gezeigt wird. Auch sind die mit verschiedenen Datierungsmethoden (Rb-Sr, Sm-Nd, K-Ar) an Mineralseparaten und teilweise an Gesamtgestein ermittelten Alter konsistent und machen eine metamorphe Überprägung unwahrscheinlich. Aufgrund der Verteilung der primordialen Edelgasisotope zwischen Fluideinschlüssen und Gesteinsmatrix ist ein langsamer Magmenaufstieg anzunehmen, was die Möglichkeit der Kontamination mit einem krustalen Fluid während des Magmenaufstiegs erhöht.

Die Gasextraktion aus Mineralseparaten erfolgte thermisch, wodurch eine Freisetzung der Gase ausschließlich aus Fluideinschlüssen nicht möglich ist. Hierbei zeigen Amphibol und Klinopyroxen, separiert aus Kostamuksha-Lamproiten, in ihrer Neon-Isotopenzusammensetzung im Vergleich zur krustalen Zusammensetzung (Kennedy et al., 1990) ein leicht erhöhtes Verhältnis von ²⁰Ne/²²Ne, was ein Hinweis auf Mantel-Neon sein könnte. Kalifeldspäte, Quarz und Karbonate enthalten dagegen nur Neon krustaler Zusammensetzung. Phlogopite haben sehr kleine Verhältnisse von ²⁰Ne/²²Ne und ²¹Ne/²²Ne, zurückzuführen auf in-situ-Produktion von ²²Ne in Folge von U- und Th-Zerfallsprozessen.

Wie unterschiedliche thermische Entgasungsmuster für ⁴⁰Ar und ³⁶Ar zeigen, ist ³⁶Ar in Fluideinschlüssen konzentriert. Das ⁴⁰Ar/³⁶Ar-Isotopenverhältnis der Fluideinschlüsse von Lamproiten aus Kostamuksha ist antikorreliert mit der durch thermische Extraktion bestimmten Gesamtmenge an ³⁶Ar. Argon aus Fluideinschlüssen setzt sich daher aus zwei Komponenten zusammen: Einer Komponente mit atmosphärischer Argon-Isotopenzusammensetzung und einer krustalen Komponente mit einem Isotopenverhältnis ⁴⁰Ar/³⁶Ar > 6000. Diffusion von radiogenem ⁴⁰Ar aus der Kristallmatrix in die Fluideinschlüsse spielt keine wesentliche Rolle.

Kimberlite aus Poria Guba und Kandalaksha zeigen anhand der Helium- und z. T. auch der Neon-Isotopenzusammensetzung eine Mantelkomponente in den Fluideinschlüssen an. Bei einem angenommenen ²⁰Ne/²²Ne-Isotopenverhältnis von 12,5 in der Mantelquelle ergibt sich ein ²¹Ne/²²Ne-Isotopenverhältnis von 0,073 ± 0,011 sowie ein ³He/⁴He-Isotopenverhältnis, welches im Vergleich zum subkontinentalem Mantel (Dunai und Baur, 1995) stärker radiogen geprägt ist. Solche Isotopensignaturen sind mit höheren Konzentrationen an Uran und Thorium in der Mantelquelle der Kimberlite zu erklären.

Rb-Sr- und Sm-Nd-Altersbestimmungen erfolgten von russischer Seite (Belyatskii et al., 1997; Nikitina et al., 1999) und ergeben ein Alter von 1,23 Ga für den Lamproitvulkanismus in Kostamuksha. Eigene K-Ar-Datierungen an Phlogopiten und Kalifeldspäten stimmen mit einem Alter von 1193 ± 20 Ma fast mit den Rb-Sr- und Sm-Nd-Altern überein. Die K-Ar-Datierung an einem Phlogopit aus Poria Guba, separiert aus dem Kimberlit PGK 12a, ergibt ein Alter von 396 Ma, ebenfalls in guter Übereinstimmung mit Rb-Sr-und Sm-Nd-Altern (ca. 400 Ma, Lokhov, pers. Mitteilung). K-Ar-Altersbestimmungen an Gesamtgestein aus Poria Guba erbrachten kein schlüssiges Alter. Die Rb-Sr- und Sm-Nd-Alter des Lamproitmagmatismus in Poria Guba betragen 1,72 Ga (Nikitina et al., 1999).

Vergleiche von gemessenen mit berechneten Edelgaskonzentrationen aus in-situ-Produktion zeigen weiterhin, dass in Abhängigkeit vom Alter der Probe Diffusionsprozesse stattgefunden haben, die zu unterschiedlichen und z. T. erheblichen Verlusten an Helium und Neon führten. Diffusionsverluste an Argon sind dagegen kaum signifikant. Unterschiedliche Diffusionsverluste in Abhängigkeit von Alter und betrachtetem Edelgas zeigen auch die primordialen Edelgase.
In the present thesis, interactions of kimberlites and lamproites as well as their constituent minerals with fluids are discussed based on noble gas compositions. The samples originate from the eastern Baltic Shield, more specifically from the Kola craton (Poria Guba and Kandalaksha) and the Karelia craton (Kostamuksha). Gas was extracted by stepwise heating and crushing from 23 whole rock samples and 15 mineral separates. These two techniques allow differential extraction of gas from fluid inclusions (crushing technique) and from the bulk sample (stepwise heating). The noble gas analyses provide the following information:

Helium and neon isotopic compositions of fluid inclusions in lamproites reveal the presence of a crustal fluid phase. Fluid interaction probably ocurred already during the process of magma ascent. Interaction after lamproite emplacement seems unlikely. The lamproites and their host rock differ in the degree of fluid-rock interaction, as demonstrated by the C/³⁶Ar composition. In addition, various dating methods (Rb-Sr, Sm-Nd, K-Ar) yield almost the same age within analytical error. Thus, a metamorphic overprint can be excluded. The distribution of primordial noble gases between fluid inclusions and crystal lattice suggests a relatively slow magma ascent, making an interaction of the lamproitic magma with crustal fluids even more likely. Since noble gases from mineral separates were extracted only by the stepwise heating method, gases stored in fluid inclusions could not be released separately.

Amphibole and clinopyroxene separates yielded a higher ²⁰Ne/²²Ne ratio in comparison to crustal composition (Kennedy et al., 1990). This presumably is an indication of a mantle derived fluid phase. On the other hand, neon isotopic composition of K-feldspar, quartz and carbonate separates are indistinguishable from the crustal composition. In comparison to other mineral separates, phlogopite yields very low ratios of ²⁰Ne/²²Ne and ²¹Ne/²²Ne due to in situ production of ²²Ne, which is a result of nuclear reactions.

The distinct thermal gas release patterns of ⁴⁰Ar and ³⁶Ar indicates that ³⁶Ar is concentrated in fluid inclusions. The ⁴⁰Ar/³⁶Ar isotopic ratio in fluid inclusions shows a negative correlation with the total amount of ³⁶Ar released by thermal extraction. Therefore, argon from fluid inclusions is a simple 2-component mixture of air and a crustal component with an ⁴⁰Ar/³⁶Ar ratio > 6000. It can be shown that diffusion of ⁴⁰Ar from the matrix into fluid inclusions is negligible.

In contrast to lamproites, whole rock kimberlite samples from Poria Guba and Kandalaksha show clear evidence in helium and, to a certain extentalso in neon isotope ratios, of interaction with a mantle derived fluid phase. Assuming a ²⁰Ne/²²Ne ratio of 12.5 for the mantle endmember, a ²¹Ne/²² Ne ratio of 0.073 ± 0.011 can be calculated. Likewise, the resulting ³He/⁴He ratio is more strongly influenced by radiogenic helium in comparison to the mean subcontinental mantle (Dunai und Baur, 1995). Such behaviour reflects higher concentrations of uranium and thorium in the magma source of kimberlites than the subcontinental mantle.

Rb-Sr and Sm-Nd age determinations (Belyatskii et al., 1997; Nikitina et al., 1999) yield 1.23 Ga for the lamproite magmatism in Kostamuksha. K-Ar dating of phlogopite and K-feldspar provides similar ages (1.19 Ga). K-Ar dating of a single phlogopite separate from the Kimberlite sample PGK12a from Poria Guba, yields an age of 396 Ma which corresponds well with Rb-Sr and Sm-Nd ages.

Depending on sample age, distinct and partly extensive diffusive loss of helium and neon has occurred, as shown by comparison of measured and calculated concentrations of in situ produced isotopes. Diffusion loss is negligible for argon. This is also strongly supported by primordial noble gas composition.

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Pinto, Victor Hugo. « Linking tectonic evolution with fluid history in hyperextended rifted margins : examples from the fossil Alpine and Pyrenean rift systems, and the present-day Iberia rifted margin ». Thesis, Strasbourg, 2014. http://www.theses.fr/2014STRAH018/document.

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Cette thèse est centrée sur la caractérisation des traceurs des fluides qui interagissent avec les roches du socle et les roches sédimentaires dans les systèmes riftés hyper-amincis exposés dans la Téthys alpine, les Pyrénées et Ibérie-Terre Neuve. L’étude de ces fluides est basée sur les observations géologiques, les analyses géochimiques et les données géophysiques. Deux types de fluides ont été identifiés : les fluides associés à la croûte continentale, avec une signature caractérisée par Si et Ca, ainsi que les fluides liés au manteau en exhumation, avec une signature caractérisée par Si, Mg, Fe, Mn, Ca, Ni, Cr et V. La percolation des fluides est fortement liée à la formation des failles de détachement et à l’évolution des systèmes hyper-amincis. Le flux de fluides dans ces systèmes a des implications importantes pour les changements rhéologiques, pour la nature des sédiments et pour les modifications chimiques des réservoirs de la Terre
This thesis focus in the identification of geochemical tracers and effects of fluid that interact with basement and sedimentary rocks in hyperextended systems. The investigation of such fluids is based on geological observation, geochemical analyses and geophysical data from fossil hyperextended rift systems exposed in the Alps and in the West Pyrenees, and the present-day distal margins of Iberia and Newfoundland. Two types of fluids were identified during this study. The first type, referred to as continental crust-related fluids, has a signature of Si and Ca. The second type, referred to as mantle-related fluids, has a signature of Si, Mg, Fe, Mn, Ca, Ni, Cr and V. The fluid percolation is strongly related to the formation of extensional detachment faults and the evolution of hyperextended systems. Fluid flow in these systems has major implications for the nature of sediments, rheological changes and chemical modifications of the Earth’s reservoirs throughout its evolution

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Kumagai, Yoshitaka. « Carbon dioxide bearing saline fluid inclusions in mantle xenoliths from the Ichinomegata volcano, the Northeast Japan arc and their evolution in the mantle wedge ». 京都大学 (Kyoto University), 2015. http://hdl.handle.net/2433/199111.

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Pears, M. I. B. « Stall and collapse in mantle plumes : an experimental and numerical fluid dynamics perspective ». Thesis, University College London (University of London), 2015. http://discovery.ucl.ac.uk/1465981/.

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Collapsing thermal plumes were investigated through experimental and numerical simulations. Collapsing plumes are an uncommon fluid dynamical phenomenon, usually observed when the heat source is removed. A series of fluid dynamical experiments were conducted on thermal plumes at a variety of temperature and viscosity contrasts, in a cubic plexiglas tank of inner side dimension 26.5cm and no-slip sides. The fluid was heated by a small 2cm diameter heater. Experimental fluids included Lyle’s Golden syrup and ADM’s Liquidose 436 syrup, which have strongly temperature-dependent viscosities and high Prandtl numbers (10³-10⁵ at experimental conditions). Visualisation techniques included white light shadowgraphs and Stereoscopic Particle Image Velocimetry (SPIV) of the tank's central plane. Temperature contrasts ranged from 3-60°C, and two differing forms of collapse were identified. At very low temperature differences stalled collapse was observed, where the plumes stall in the lower third of the tank before collapsing. At temperature differences between 7-23°C normal plume evolution occurred, until lenticular collapse developed between midway and two-thirds of the distance from the base of the tank. The lens shape originated in the top of the head and was present throughout collapse. At temperatures above ΔT=23°C, the plumes followed the expected growth and shape and the head flattened out at the top of the tank. Thermal collapse remains difficult to explain given experimental conditions (continuous heating). Instead, it is possible that small density differences arising from crystallisation at ambient temperatures changes plume buoyancy and therefore induces lenticular collapse. The evolution of the refractive index of the syrup through time to ascertain this possibility was measured. Additionally, SPIV revealed the presence of a large, downwelling, low velocity mass in the tank that inhibited the growth of low temperature difference stalled collapse plumes. In the mantle it is likely that the stalled collapse plumes would be unable to be detected by tomography because they would be unable to traverse far from the thermal boundary layer and would collapse back to the base. This would mean that they would have little impact on redistributing material in the mantle. The plumes in this stalled collapse regime had rise times comparable to diffusion times, which is an additional reason for the collapse. The lenticular collapse in the mantle could cause depletion of a deep-source and redistribute the material in the region where the plume began to collapse with some material flowing back to the base of the mantle. Numerical simulations using Fluidity (Fluidity, is an adaptive mesh finite element package) were undertaken to explore the parameter range where the two collapse phenomena were observed experimentally. These simulated plumes did not show signs of collapse in the purely thermal simulation but at temperature differences up to 14°C the plumes stalled and were unable to ascend to the top of the tank. The aspect ratio of the tank was changed to explore the effect this had on plume stalling. At increased tank height the plume ascended further in the tank whilst the conduit radius remained constant. However, the very low temperature difference plumes remained unable to reach the upper surface of the tank. In contrast, when the tank width was increased the plumes ascended a little further in the tank but stalled at an earlier time and the plume conduit width generally increased. This implied that the tank width was inhibiting the growth of the plume marginally. Therefore, changing the aspect ratio of the tank does not inhibit the stalling of the simulated plumes and is unlikely to be influencing the experimental plumes growth, stalling and collapse.

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McQuarrie, Shane Alexander. « Data Assimilation in the Boussinesq Approximation for Mantle Convection ». BYU ScholarsArchive, 2018. https://scholarsarchive.byu.edu/etd/6951.

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Many highly developed physical models poorly approximate actual physical systems due to natural random noise. For example, convection in the earth's mantle—a fundamental process for understanding the geochemical makeup of the earth's crust and the geologic history of the earth—exhibits chaotic behavior, so it is difficult to model accurately. In addition, it is impossible to directly measure temperature and fluid viscosity in the mantle, and any indirect measurements are not guaranteed to be highly accurate. Over the last 50 years, mathematicians have developed a rigorous framework for reconciling noisy observations with reasonable physical models, a technique called data assimilation. We apply data assimilation to the problem of mantle convection with the infinite-Prandtl Boussinesq approximation to the Navier-Stokes equations as the model, providing rigorous conditions that guarantee synchronization between the observational system and the model. We validate these rigorous results through numerical simulations powered by a flexible new Python package, Dedalus. This methodology, including the simulation and post-processing code, may be generalized to many other systems. The numerical simulations show that the rigorous synchronization conditions are not sharp; that is, synchronization may occur even when the conditions are not met. These simulations also cast some light on the true relationships between the system parameters that are required in order to achieve synchronization. To conclude, we conduct experiments for two closely related data assimilation problems to further demonstrate the limitations of the rigorous results and to test the flexibility of data assimilation for mantle-like systems.

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Prigent, Cécile. « (Dé)formation d'un coin mantellique en initiation de subduction : étude intégrée de la base mantellique de l'ophiolite d'Oman ». Thesis, Université Grenoble Alpes (ComUE), 2017. http://www.theses.fr/2017GREAU005/document.

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Les processus affectant le coin mantellique situé au-dessus d’une zone de subduction (déformation et interaction avec les fluides/liquides magmatiques libérés par la plaque inférieure) ont des implications importantes sur la dynamique de la subduction et le budget géochimique global de la Terre.Afin de mieux contraindre ces processus, ma thèse a porté sur l’étude de l’unité rubanée de l’ophiolite du Semail. Cette unité de 200-500m d’épaisseur s’est (dé)formée, juste au-dessus de l’interface interplaque, pendant l’initiation de la subduction ou du chevauchement intra-océanique (qui a mené, à terme, à l’obduction de l’ophiolite). Elle est en effet située au-dessus de la semelle métamorphique HT (amphibolites à granulites ; 750-850°C et 0.9-1.1GPa) interprétée comme des écailles de la plaque inférieure métamorphisées et sous-plaquées à la plaque supérieure (actuelle ophiolite) lors des premiers stades de la convergence.Après une caractérisation structurale de terrain de cette unité rubanée et la collecte de plus de200 échantillons tout le long de l’ophiolite, j’ai mené une analyse intégrée (Microscopie optique, MEB, microsonde, EBSD, (LA-)ICPMS) sur une sélection d’entre-eux, afin de caractériser l’évolution P-T, pétrologique, géochimique et structurale des péridotites de l’unité rubanée pendant cet épisode de déformation.Les résultats montrent que cette déformation a mené à la formation de zones de cisaillement (proto)mylonitiques (~850-750°C) puis ultramylonitiques (~750-650°C) et que cette déformation BT s’est faite en décompression (d’~3kbar, i.e. 10km). Les résultats pétrologiques indiquent que des fluides silicatés hydratés ont percolé à travers (et intéragi avec) ces péridotites pendant cette déformation. Ces processus d’interaction ont mené à (1) la précipitation de minéraux métasomatiques (Ol+Opx+Cpx+Spl+Amp±Sulf), et (2) l’enrichissement des phases en éléments mobiles dans les fluides (surtout B, Li et Cs :concentrations de 1 à 40 fois celles du manteau primitif).L’analyse des isotopes du bore (δ11B des péridotites métasomatisées jusqu’à +25‰) démontre que ces fluides ont une signature de subduction et qu’ils sont vraisemblablement issus de la déshydratation de la semelle HT lors de sa formation à 750-850°C.En combinant ces résultats avec une analyse microstructurale, j’ai ensuite étudié les mécanismes et les rétroactions entre la circulation de ces fluides, la déformation des péridotites et la localisation de cette déformation. A l’échelle macroscopique, on observe une focalisation des fluides dans les zones de cisaillement actives, associée à une localisation progressive de la déformation.Nous avons aussi exploré les conséquences rhéologiques de l’hydratation de ce manteau sur le régime, couplé ou découplé, de l’interface. Les lois rhéologiques indiquent que l’affaiblissement des (proto)mylonites de l’unité rubanée, par hydratation, peut expliquer le couplage de l’interface de subduction à 850-750°C et, ainsi, l’accrétion de la semelle HT. Nous interprétons les zones de cisaillement ultramylonitiques ultérieures (~750-650°C) comme étant liées au stade d’exhumation simultanée de l’unité rubanée et de la semelle HT d’environ 10km au-dessus de l’interface, jusqu’à leur position actuelle sous l’ophiolite.Les résultats de cette étude suggèrent donc que l’interface semelle HT/unité rubanée représente une interface de subduction fossilisée et le manteau (proto)mylonitique sus-jacent, un coin mantellique qui s’est (dé)formé et a intéragi avec des fluides de subduction pendant l’initiation de la subduction. L’unité rubanée de l’ophiolite du Semail représente donc un des rares objets géologiques permettant d’étudier les processus à l’oeuvre dans un coin mantellique, et d’en traquer, avant sa fossilisation, les transformations mécaniques et chimiques sur ~1 million d’années
The processes affecting the mantle wedge atop a subduction zone (deformation and interaction with fluids/melts released by the downgoing plate) play a major role on subduction zones dynamics and the global geochemical budget of the Earth.To better constrain these processes, my Ph.D. research project has focused on studying the basal banded unit of the Semail ophiolite. This 200-500m thick peridotitic basal unit was (de)formed, directly above the interplate interface, during the intra-oceanic subduction (or underthrusting) initiation (that ultimately led to the ophiolite obduction). The banded unit indeed overlies the HT metamorphic sole (amphibolites to granulites ; 750-850°C and 0.9-1.1GPa) interpreted as slices of the downgoing plate underplated to the upper plate (the ophiolite) during early subduction (or subduction "infancy").After a field-based structural characterization of this banded unit and more than 200 samples collected all along the strike of the ophiolite, I carried out an integrated analysis (Optical microscopy, SEM, microprobe, EBSD, (LA-)ICPMS) on selected samples, in order to constrain the P-T, petrological, geochemical and structural evolution of the banded unit peridotites during this deformation event.Our results show that this deformation led to the formation of (proto)mylonitic (at ~850-750°C) then ultramylonitic (at ~750-650°C) shear zones and that this deformation was associated with peridotites decompression (of ~3kbar, i.e. 10km). Petrological results suggest that hydrated silicate fluids have percolated through (and interacted with) these peridotites during their deformation. These interaction processes triggered (1) the precipitation of metasomatic minerals (Ol+Opx+Cpx+Spl+Amp±Sulf), and (2) the enrichment of phases in fluid mobile elements (parti- cularly B, Li and Cs;concentrations from 1 to 40 times higher than those of the primitive mantle).The analysis of boron isotopes (δ11B of metasomatized peridotites up to +25‰) demonstrated that these fluids had a "subduction signature" and that they presumably derived from HT sole dehydration while forming at 850-750°C.By combining these results with microstructural analyses, I then studied the mechanisms and feedbacks between the circulation of these fluids, peridotites ductile deformation and strain localization. At the macroscopic scale, we observe a focusing of fluids in actively deforming peridotites associated to progressive strain localization during peridotites cooling.We also investigated the rheological consequences of banded unit peridotites hydration on the regime (coupled or decoupled) of the interface. Rheological laws indicate that the hydration-related weakening of banded unit (proto)mylonites is able to explain the coupling of the subduction inter- face at 850-750°C and, thereby, HT sole slicing and accretion. We interpret the later development of the ultramylonitic shear zones (at ~750-650°C) as being associated to the subsequent exhumation stage, i.e. the coeval exhumation of the banded unit and the HT metamorphic sole over around10km along the interface, up to their present-day position under the ophiolite.The results of this work suggest that the HT sole/banded unit contact represents a fossilized subduction interface and the overlying (proto)mylonitic mantle, a frozen-in mantle wedge that was (de)formed and interacted with subduction fluids during subduction infancy. The Semail ophiolite banded unit therefore provides a rare glimpse of processes affecting a mantle wedge, and enables tracking its mechanical and geochemical transformations over 1My (prior to its fossilization).The processes highlighted in this Ph.D. research project thus bring new constraints on the (petrological-geochemical-rheological) consequences of mantle wedge peridotites interaction with subduction fluids

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Hauri, Erik Harold. « Geochemical and fluid dynamic investigations into the nature of chemical heterogeneity in the Earth's mantle ». Thesis, Massachusetts Institute of Technology, 1992. http://hdl.handle.net/1721.1/54358.

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Kosman, Charles Walter. « Cretaceous mantle of the Congo craton : evidence from mineral and fluid inclusions in Kasai alluvial diamonds ». Thesis, University of British Columbia, 2015. http://hdl.handle.net/2429/56236.

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Alluvial diamonds from the Kasai River, Katanga Province, Democratic Republic of the Congo (DRC), were studied in order to constrain the composition, thermal state, and diamond forming fluids of the ancient lithospheric mantle of the Congo craton. The diamonds originate from Cretaceous kimberlites of the Lucapa graben in northeastern Angola. We report carbon isotope compositions (δ¹³CVPDB), nitrogen concentrations ([N]), and nitrogen aggregation states of 138 diamonds, as well as compositions of mineral and fluid inclusions in the diamonds. Diamonds emplaced by kimberlites of the northeastern Lucapa graben and eroded into alluvials along the Kasai river contain 25–2900 ppm [N], show 0–88% N aggregation and δ¹³C isotopic compositions spanning -27‰ to -2‰ with a mode near mantle-like values. In situ cathodoluminescence (CL), secondary ion mass spectrometry (SIMS) and Fourier transform infrared spectroscopy (FTIR) reveal large heterogeneities in [N], N aggregation and δ¹³C, indicating diamonds grew episodically from fluids of distinct sources. Fluid inclusion compositions of fibrous diamonds analyzed by electron probe microanalysis are moderately to highly silicic, matching compositions of diamond-forming fluids from other DRC diamonds. Regional homogeneity of Congo fibrous diamond fluid inclusion compositions suggests spatially extensive homogenization of Cretaceous diamond forming fluids within the Congo lithospheric mantle. Electron probe microanalysis (EPMA) of trapped silicate inclusions revealed both peridotitic (Fo₉₁₋₉₅ and En₉₂₋₉₄, 78% of the suite) and eclogitic parageneses (Cr-poor pyrope and omphacite with 11–27% jadeite, 17% of the suite) within diamonds (11% remainder unknown). Clinopyroxene-garnet thermobarometry suggest diamond formation at 1350–1375 °C, whereas [N] aggregation thermometry yields diamond residence temperatures between 1000 and 1275 °C, if the assumed residence time is 0.9–3.3 Ga. Integrated geothermobaromtery indicates heat fluxes of 41–45 mW/m² during diamond formation and a shallow lithosphere-asthenosphere boundary (LAB) 175–189 km. The shallow LAB may result from a higher than average cratonic geotherms and the position of the Kasai block near the Congo cratonic margin. The hotter mantle may be attributable to contemporaneous rifting of the southern Atlantic, multiple post-Archean reactivations of the craton, and/or proximal Cretaceous plumes.
Science, Faculty of
Earth, Ocean and Atmospheric Sciences, Department of
Graduate

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Goncharov, Aleksey. « Redox - pressure - temperature conditions in the continental upper mantle in relation to C-O-H fluid speciation ». Phd thesis, Université Jean Monnet - Saint-Etienne, 2012. http://tel.archives-ouvertes.fr/tel-00974462.

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The thesis is based on a petrologic and geochemical study of mantle xenoliths from the central Siberian craton and the Baikal-Mongolia region of central Asia. Its goal is to establish the redox regime of the lithospheric mantle in these two domains with distinct tectonic settings and age and relate it to thermal regime and the speciation of C-0-H fluids. Oxygen fugacity is calculated based on Fe2+/Fe3+ ratios in spinel and garnet of mantle peridotites obtained by Mössbauer spectroscopy. The study deals with the following topics: (i) microstructures, chemical and mineralogical composition of the xenoliths; (ii) Fe2+/Fe3+ ratios in minerals by Mössbauer spectroscopy; (iii) equilibration temperatures and pressures using mineral thermo-barometry; (iv) oxygen fugacity from mineral compositions using oxybarometry; (v) proportions of molecular components in C-0-H fluids coexisting with the studied rocks. The three main conclusions of this study are: (1) Oxygen fugacity in the lithospheric mantle in the central Siberian craton decreases from +1 to -4 ΔlogʄO2 (FMQ) at depths from 70 to 220 km and shows significant lateral variations. (2) The lithospheric mantle beneath the Baikal-Mongolia region shows important redox heterogeneities, with a sharp decrease in oxygen fugacity (from +0 to -3 AlogfO2 (FMQ)) during the transition from the spine! to garnet facies peridotites at 50 to 90 km. (3) The speciation of C-O-H fluids changes with depth from essentially H2O-CO2 in the shallow lithospheric mantle to H2O-CH4 at the lithosphere-asthenosphere boundary regardless of the thermal state and the thickness of the lithosphere

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RIZZO, ANDREA LUCA. « The composition of noble gas and CO2 in the European subcontinental lithospheric mantle ». Doctoral thesis, Università degli studi di Ferrara, 2020. http://hdl.handle.net/11392/2487890.

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This PhD thesis reports an integrated study of petrography and geochemistry of the minerals with noble gases and CO2 (when available) in fluid inclusions (FI) from selected mantle xenoliths erupted in Europe during alkaline magmatism. The aim of the thesis is to show how the occurrence of partial melting, metasomatism, refertilization, magmatic degassing, volatile recycling, and mixing of volatiles modified the pristine composition of fluids stored in European SCLM and give clues on its geodynamic evolution. Mantle xenoliths from a few key regions where magmatism occurred in different temporal and geodynamic conditions were selected: Lower Silesia (Eger Rift) in SW Poland, Persani Mts. (Transylvania) in Romania, Eifel and Siebengebirge in Germany. The main outcomes of this thesis are: -The chemistry of FI in mantle xenoliths from the studied areas revealed is dominated by CO2, with N2 as second major species. Noble gas are in trace. Oliv are systematically gas-poor respect to Px from the same xenoliths. Among Oliv from European xenoliths, those from Lower Silesia display the highest CO2 concentrations suggesting carbonated-like metasomatism, as also inferred from trace elements in cpx. -Ne and Ar concentration and isotopic ratios indicate variable extents of contamination by atmosphere-derived fluids. This contamination is likely derived from the recycling into the mantle of atmospheric-derived material inherited by local/recent or fossil subduction. This is more evident in the xenoliths from Persani Mts., where a recent subduction occurred. -Oliv and Px display variable extents of partial melting and metasomatism/refertilization, as indicated by the mineral chemistry and He/Ar* in FI. The highest degrees of melting (25-30%) are found in samples from Lower Silesia and Siebengebirge, which are also among the oldest within the suite of samples (>6 Ma). Evidences of low degrees of melting and/or refertilization are found in Persani Mts. and West Eifel, which are Quaternary. This suggests that refertilization process is likely occurred in Quaternary, postponing mantle melting still recorded in Lower Silesia and Siebengebirge. -The 3He/4He corrected for air contamination (Rc/Ra) is within European SCLM range (6±1 Ra) that is lower than MORB (8±1 Ra). This indicates a widespread recycling of crustal material below Europe if compared to other continental rift (e.g., Antarctica, East African). However, the careful investigation of olivine, cpx, and opx in single localities allowed distinguishing variations of 3He/4He that are related to the local history of the mantle. In detail, Persani Mts. show the lowest 3He/4He values within the dataset that indicate highest degree of crustal recycling due to the recent subduction that plays an important role in contaminating the mantle. Instead, metasomatism involving asthenospheric MORB-like fluids well explains the highest 3He/4He values recognized in all the studied localities. -Ne-Ar-He isotopic systematics indicates that most of the data fall along a mixing between air and a MORB mantle. The presence of a plume (lower mantle) beneath the studies localities can be excluded. -I presented the first data of carbon isotope composition of CO2 (δ13C V-PDB) in the Lower Silesia mantle xenoliths, which suffered a metasomatism by carbonated-rich fluids. The δ13C values are about -3.9 ‰ and are within MORB range with <0.1% limestone contamination. -The comparison of 3He/4He signature measured in mantle xenoliths from the three target areas with that of CO2-dominated gas emissions located within or nearby shows that only gases emitted along Eger Rift are representative of the local mantle signature, suggesting an active magmatic activity below this area. Instead, gases emitted in East Eifel and nearby Persani Mts. are slightly to strongly contaminated by crustal fluids during their rising toward the surface or are released from a cooling and aging magma residing within the crust.
Questa tesi riporta lo studio integrato di petrografia e geochimica dei minerali con gas nobili e CO2 in inclusioni fluide (FI) di xenoliti di mantello eruttati in Europa durante il magmatismo alcalino. Lo scopo della tesi è mostrare come il verificarsi di fusione parziale, metasomatismo, rifertilizzazione, degassamento magmatico, riciclo e miscelazione di volatili nel mantello abbia modificato la composizione originaria del mantello litosferico sub-continentale Europeo e fornito indizi sulla sua evoluzione geodinamica. Sono stati selezionati campioni provenienti da alcune regioni in cui si è verificato il magmatismo in diverse condizioni temporali e geodinamiche: Bassa Silesia (Eger Rift) nella Polonia meridionale, Mt. Persani (Transilvania) in Romania, Eifel e Siebengebirge in Germania. I principali risultati di questa tesi sono: -La composizione chimica delle FI negli xenoliti delle aree studiate è dominata dalla CO2, con N2 come seconda specie principale. I gas nobili sono in traccia. Le Olivine (Ol) sono sistematicamente povere di gas rispetto ai pirosseni (Px) degli stessi xenoliti. Tra i campioni studiati, le Ol della Bassa Silesia mostrano le più alte concentrazioni di CO2 che suggeriscono un metasomatismo carbonatato, come dedotto anche dagli elementi in traccia nei Px. -La concentrazione ed i rapporti isotopici di Ne e Ar indicano variabili gradi di contaminazione da parte di fluidi atmosferici. Questa contaminazione è causata dal riciclo nel mantello di materiale derivato dall'atmosfera ereditato dalla subduzione locale, recente o fossile. Ciò è più evidente negli xenoliti di Mt. Persani, dove si è verificata una subduzione recente. -Oliv e Px mostrano variabili percentuali di fusione parziale e metasomatismo/rifertilizzazione, come indicato dalla chimica dei minerali e dall’He/Ar* nelle FI. I più alti gradi di fusione (25-30%) si trovano in Bassa Silesia e Siebengebirge, che sono anche tra i più antichi all'interno della suite di campioni (>6 Ma). Bassi gradi di fusione e/o rifertilizzazione sono ipotizzati nei Mt. Persani e nella parte occidentale dell’Eifel, che sono quaternari. Ciò suggerisce che il processo di rifertilizzazione è avvenuto nel Quaternario. -Le misure di 3He/4He corretto per la contaminazione dell'aria (Rc/Ra) rientrano nell'intervallo di valori noto per il mantello Europeo (6±1 Ra) e sono inferiori a quello MORB (8±1 Ra). Ciò indica un diffuso riciclo di materiale crostale al di sotto dell'Europa rispetto ad altre zone di rift continentale (ad es. Antartide, Africa orientale). Tuttavia, l'attenta indagine su Oliv e Px nelle singole località ha permesso di distinguere le variazioni di 3He/4He correlate alla storia locale del mantello. Nel dettaglio, i Mt. Persani mostrano 3He/4He più bassi, indicando il più alto grado di riciclo di materiale crostale nel mantello. Invece, il metasomatismo da fluidi astenosferici simili al MORB spiega i più elevati 3He/4He presenti in tutte le località studiate. -La sistematica di Ne-Ar-He indica un trend di mescolamento tra l'aria e un mantello MORB e l’assenza di un contributo del mantello inferiore (plume) al di sotto dell’Europa. -I primi dati sulla composizione isotopica del carbonio di CO2 (δ13C V-PDB) negli xenoliti del mantello carbonatato della Bassa Silesia indicano valori di circa -3.9 ‰, che rientrano nel range MORB con una contaminazione di carbonati <0.1%. -Il confronto tra gli 3He/4He misurati negli xenoliti di mantello delle tre aree e quelli dei gas emessi all'interno o nelle vicinanze mostra che solo i gas emessi lungo l’Eger Rift sono rappresentativi della firma del mantello locale, suggerendo un'attività magmatica ancora attiva sotto quest’area. Invece, i gas emessi nell'Eifel e nelle vicine dei Mt. Persani sono variabilmente contaminati da fluidi crostali acquisiti durante la loro risalita verso la superficie o sono rilasciati da un magma in raffreddamento e invecchiamento all'interno della crosta

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SANDOVAL, VELASQUEZ Andres Libardo. « Noble gas and CO2 isotopic signatures of the lithospheric mantle underneath Mexico and the Canary Islands : clues from mantle xenoliths and arc lavas ». Doctoral thesis, Università degli Studi di Palermo, 2022. http://hdl.handle.net/10447/533636.

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Studying the isotopic composition of fluids trapped in mantle xenoliths opens avenues to understand the origin and cycling of volatiles in the Earth’s upper mantle. In this PhD dissertation, new and in most cases the very first data regarding the isotopic (noble gases and CO2) characterization of the lithospheric mantle portions of three different geodynamic environments are presented: (i) Central and NW Mexico, a continental setting dominated by extension; (ii) the Transmexican Volcanic Belt (TMVB) a subduction setting, and (iii) the Canary Islands, particularly El Hierro and Lanzarote, two oceanic islands formed by mantle plume-derived intraplate volcanism. In total 32 peridotites (including spinel lherzolites, spinel harzburgites, 1 pyroxenite and 1 dunite) and four arc lavas (from the TMVB) were investigated. To characterize the isotopic signature of the Mexican lithospheric mantle, the present work was focused on the analysis of fluid inclusions entrapped in mantle xenoliths found in pyroclastic deposits of the Ventura Espiritu Santo Volcanic Field (VESVF), the Durango Volcanic Field (DVF), the San Quintin Volcanic Field (SQVF) (three Quaternary monogenetic volcanic fields formed in the Basin and Range extensional province). Fluid inclusions in olivine phenocrysts found in arc lavas from the Sierra Chichinautzin Volcanic Field (SCN) (a Quaternary monogenetic field located in the Transmexican Volcanic Belt (TMVB)) were also analyzed. According to the petrographic analysis, all xenoliths exhibit similar mineralogy (Ol> Opx> Cpx >> Sp). The VESVF xenoliths, in particular, bring textural evidence of interstitial glass veins bearing dendritic trails of secondary melt and fluid inclusions related to pervasive mantle metasomatism driven by carbonate-rich silicate melts. Inclusions are composed of silicate glass ± CO2 ± Mg-Ca carbonates ± pyrite as indicated by Raman microspectroscopy. Excluding samples possibly affected by secondary processes, the averages Rc/Ra ratios (3He/4He ratios corrected for atmospheric contamination) measured in Mexican localities are within the MORB-like range: VESVF = 7.39 ± 0.14 Ra (1SD, n = 30), DVF= 8.39 ± 0.24 Ra (1SD, n = 10), SQVF = 7.43 ± 0.19 Ra (1SD, n = 1) and SCN lavas = 7.24 ± 0.33 Ra (1SD, n = 4). This noble gas similarity between the VESVF and SCN samples supports the existence of a homogeneous mantle in central Mexico. The 3He/4He signatures observed in xenoliths suggest that (i) either the mantle He budget was scarcely modified by the Farallon plate subduction, and/or (ii) that any (large) crustal contribution was masked by a later metasomatism/refertilization episode, possibly driven by the upwelling mantle from the asthenosphere and the subsequent Basin and Range extension. The association between glass veins and fluid inclusions in VESVF xenoliths revealed that the metasomatism/ refertilization was driven by a silicate-rich melt which is consistent with a calculated helium residence time in the VESVF mantle (20 to 60 Ma) that overlaps the timing of the above geodynamic events. It is proposed that, after the refertilization event (e.g., over the last ~20 Ma), the lithospheric mantle has evolved in a steady-state, becoming slightly more radiogenic. The relative proximity between the DVF and the VESVF suggests a similar process should have happened beneath Durango, and that the difference in 3He/4He ratios with the VESVF is likely to be associated with different ages of mantle refertilization and He residence times (more recent for the DVF mantle; 4 to 10Ma). The Ar and Ne systematics reflect a mixing between MORB-like upper mantle and atmosphere-derived fluids. The mantle beneath the SQVF and the DVF seems to be more impacted by the interaction with atmospheric fluids, as proved by a systematic decrease in 40Ar/36Ar and 4He/20Ne ratios from central (VESVF) to western Mexico (DVF, SQVF) It is proposed that these atmospheric components were likely air-derived fluids recycled by the Farallon plate subduction. 3He fluxes (0.027 - 0.080 mol/g), 4He production rates (340 - 1000 mol/yr), and mantle CO2 fluxes (3.93 x 107 mol/yr to 1.18 x 108 mol/yr) were also estimated using the helium isotopic values measured in VESVF mantle xenoliths. Finally, DVF and VESVF nodules exhibit CO2/3He ratios comparable to those of the upper mantle (from 3.38 x 108 to 3.82 x 109) but more positive δ13C values (between -1.0 and -4.0‰), supporting the involvement of a recycled crustal carbonate component likely inherited by the Farallon plate subduction. Conversely, the SCN samples exhibit δ13C values within the MORB range (comparable to other values previously reported in fluid inclusions and fumaroles from Popocatépetl, Colima and Ceboruco volcanoes) and unlike the mantle beneath VESVF-DVF, indicate a negligible mantle contamination by subduction-related crustal carbon. The Canary Islands, in the central-eastern Atlantic, are among the most enigmatic Oceanic Island provinces on Earth, as the mantle source feeding their volcanism is spatially heterogeneous and with a multiplicity of involved components. Multi-isotope whole-rock studies have long revealed the presence of a recycled oceanic crust/lithosphere in the mantle. However, noble gas systematics have been more challenging to interpret, and carbon isotope data have remained sparse and incomplete. Our very first fluid inclusion data for El Hierro and Lanzarote nodules indicate carbon isotopic compositions of CO2 (δ13C) range from –2.38 to –1.23‰ in pyroxenes and from –0.19 to +0.96‰ in olivines. These unusually positive δ13C values, well above the typical upper mantle range (–8‰<–4‰), prove, for the first time, the presence of a regional recycled crustal carbon component in mantle beneath the Canary Islands. We interpret this 13C-rich component as inherited from a mantle metasomatism event(s) driven by fluids carrying carbon from subducted altered oceanic crust (AOC) and/or oceanic lithosphere (OL). Regarding noble gas isotopes, El Hierro xenoliths identify a depleted mantle source with MORB-like He signature. The average Rc/Ra ratio (3He/4He normalized to air ratio and corrected for atmospheric contamination) of 7.45±0.26 Ra (2SD, n = 14) overall indicates a marginal role played by past subduction events in modifying the local mantle He budget. Instead, Lanzarote xenoliths point to a more radiogenic mantle with an average of 5.97±0.44 Ra (2SD, n = 13) which we interpret as reflecting the involvement of an EM component. When put in the context of previous 3He/4He measurements in fluid inclusions and surface gases along the Canary archipelago, these results confirm an overall west-to-east decrease of Rc/Ra ratios (from El Hierro to Lanzarote), which may reflect a combination of i) increasing contributions of the African continental lithosphere, ii) the addition of radiogenic 4He during magma migration in the oceanic crust (whose thickness increases eastward) and/or iii) magma ageing. Finally, as proposed for Mexico, the involvement of depleted mantle-like fluids, variably admixed with air-derived components (possibly recycled via paleo-subduction event(s)), is corroborated by Ne-Ar isotopic compositions.

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Whitehouse, Helen Eleri. « Methods to assess CSF dynamics and the mechanical properties of the cerebral mantel in hydrocephalus ». Thesis, University of London, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.322325.

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Soustelle, Vincent. « Interactions entre déformation et percolation de magma ou de fluide dans le manteau à l'aplomb des zones de subduction ». Thesis, Montpellier 2, 2010. http://www.theses.fr/2010MON20151/document.

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Ce travail apporte de nouvelles contraintes sur les interactions entre déformation et processus d'hydratation et de percolation de magma ou de fluides et leurs implications sur les propriétés sismiques dans le coin mantellique. Il se base sur l'analyse de péridotites à spinelle provenant du massif de Ronda (Espagne) et deux séries de xénolites issues de zones de subduction actives (Kamchatka, Papouasie-Nouvelle-Guinée). L'étude structurale, pétrologique et géochimique de ces échantillons montrent qu'ils ont subi une percolation réactive de magma ou de fluide synchrone d'une déformation de haute température basse contrainte cohérente avec les condition PT de la base de la lithosphère ou de l'asthénosphère. Cette percolation réactive est responsable d'un enrichissement en pyroxènes localisés dans des bandes parallèles aux structures de déformation. Cet enrichissement est associé à la décroissance et à la désorientation des cristaux d'olivine. Le système de glissement dominant dans l'olivine est {0kl}[100], cela implique que la direction de polarisation rapide des ondes S dans la partie supérieure du coin mantellique est parallèle à la direction d'écoulement du manteau. L'enrichissement en pyroxène associé à une décroissance de l'intensité des OPR de l'olivine a pour conséquence une baisse non négligeable de l'anisotropie qui peut induire jusqu'à 33% d'erreur sur l'interprétation de la couche anisotrope. Un enrichissement en orthopyroxène peut entraîner une baisse du rapport Vp/Vs, mais ne peut expliquer des Vp/Vs <1,7 cartés dans certains avant-arcs. Cependant de telles valeurs peuvent être expliquées si l'anisotropie des péridotites du coin mantellique est prise en compte
This work provides new constraints on the interactions between deformation and hydration process and the percolation of melt or fluids, and their implications for seismic properties of the mantle wedge. It is based on the analysis of spinel peridotites from the massif of Ronda (Spain) and two xenolith suites from active subduction zones (Kamchatka, Papua New Guinea). The structural, petrological and geochemical of these samples show that they underwent a reactive percolation of melt or fluid, which was synchronous to a deformation event occuring under high temperature and low stress consistent with the PT conditions of the base of the lithosphere or in the asthenosphere. This reactive percolation is responsible for pyroxenes enrichment localized in bands parallel to the deformation structures. This enrichment is associated with the grain size recuction and the disorientation of the crystals of olivine. The dominant slip system in olivine is {0 kl}[100], which results in fast S-wave polarization parallel to the flow direction in the mantle. The enrichment in pyroxene, associated with a decrease in the intensity of the olivine crystal preferred orientations, results in a significant decrease of the anisotropy that may induce error on the interpretation of the anisotropic layer (up to 33%). The observed orthopyroxene enrichment also lowers the Vp/Vs ratio, but cannot explain Vp/Vs < 1.7 mapped in some fore-arc mantles. Such low Vp/Vs ratios may however be explained by considering the intrinsic anisotropy of the peridotites, which is generally ignored in large-scale Vp/Vs ratio mapping of the mantle wedge

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Baptiste, Virginie. « Stabilité et érosion du manteau lithosphérique subcontinental : Relations entre déformation, hydratation et percolation de fluides et magmas sous le craton du Kaapvaal et le Rift Est-Africain ». Thesis, Montpellier 2, 2014. http://www.theses.fr/2014MON20139/document.

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Les travaux réalisés durant cette thèse apportent de nouvelles contraintes sur les relations entre déformation, hydratation et percolation de fluides et/ou de magmas dans le manteau subcontinental sous un craton et sous un rift, et leurs implications sur son comportement rhéologique. Il repose sur l'analyse des microstructures, des OPRs et des teneurs en hydrogène de xénolites mantelliques du craton du Kaapvaal, et sur deux séries de xénolites provenant de différentes localités le long du rift Est-Africain (Divergence Nord Tanzanienne et SE de l'Ethiopie). Les microstructures granulaires à gros grains et les OPRs bien définies des péridotites du craton du Kaapvaal sont cohérentes avec un épisode de déformation suivi d'une longue période de quiescence. Les OPRs de l'olivine sont majoritairement à symétrie orthorhombique, mais des symétries axiale-[100] et axiale-[010] sont aussi mesurées. Les péridotites cratoniques enregistrent de multiples épisodes métasomatiques, ayant entraîné une hétérogénéité de compositions à petite échelle ne pouvant être détectée par les études sismiques. Les teneurs en hydrogène mesurées dans l'olivine sont variables, mais ont tendance à augmenter jusqu'à 150 km de profondeur, atteignant alors jusqu'à 50 ppm wt. H2O. En dessous de cette profondeur, les échantillons montrent des teneurs en hydrogène très faibles. Les expériences réalisées en piston-cylindre sur la diffusion de l'hydrogène issue d'un liquide kimberlitique vers de la forstérite suggèrent que la fugacité en eau pourrait fortement être diminuée par la présence de CO2, empêchant l'hydratation de l'olivine durant extraction des xénolites par les kimberlites. Ces résultats expérimentaux suggèrent que les teneurs en hydrogène dans l'olivine des péridotites du craton du Kaapvaal ont été acquises durant un épisode métasomatique en profondeur et non pendant leur extraction par les kimberlites. Ces teneurs n'ont toutefois pas à ce jour entraîné de remobilisation de la racine cratonique. Enfin, le calcul des propriétés sismiques des péridotites cratoniques révèle que les anisotropies générées par les OPRs de ces échantillons sont suffisantes pour expliquer les anisotropies mesurées par les ondes SKS et les ondes de surface.Les xénolites de la Divergence Nord-Tanzanienne, montrent des variations significatives de microstructures et d'OPR de l'olivine entre les péridotites des localités dans l'axe du rift et celles de la chaîne volcanique transverse (Lashaine et Olmani). A Lashaine, les microstructures granulaires à gros grains et les OPRs de type orthorhombique et axial-[010] peuvent être expliquée par une déformation en transpression liée à la formation de la chaîne Mozambique ou par la présence d'une relique d'un domaine cratonique à l'intérieur de la chaîne Mozambique. Dans l'axe du rift, les microstructures porphyroclastiques à mylonitiques suggèrent une déformation plus récente, accompagnée de réactions magma-roche sous des conditions proches du solidus, suivie d'un recuit variable. L'hétérogénéité des microstructures enregistrées par les échantillons du rift suggère de multiples épisodes de déformation localisée, probablement liés à l'injection percolation épisodique de magmas, espacés de périodes d'accalmie. Les OPRs de l'olivine de type axial-[100] et l'orientation des directions de polarisation des ondes SKS suggère que le rift s'est formé en régime de transtension Les péridotites du Sud-Est de l’Éthiopie présentent des microstructures porphyroclastiques à gros grains moins recristallisées qu'en Tanzanie. Les microstructures et les OPRs principalement de type orthorhombique suggèrent une déformation syn- à post-métasomatisme. Les anisotropies de polarisation des ondes S calculées pour ces échantillons sont insuffisantes pour expliquer à elles seules les déphasages des ondes SKS dans cette partie du rift
This study provides additional constraints on the relations between deformation, hydration and percolation of fluids and melts in the subcontinental lithospheric mantle beneath a craton and a rift, as well as their implication on its geodynamical behaviour. I have analysed the microstructures, the CPOs, and the hydrogen content of mantle xenoliths from the Kaapvaal craton, and two sets of xenoliths from different localities along the East African Rift (North Tanzanian Divergence and SE Ethiopia). The coarse-granular microstructures and the well-defined CPOs in Kaapvaal peridotites suggest a deformation followed by a long quiescence time. Orthorhombic olivine CPOs predominates, but axial-[100] and axial-[010] are also measured. Cratonic peridotites record multiple metasomatic episodes, leading to a significant compositional heterogeneity, which cannot be imaged by seismic studies. Olivine hydrogen contents are variable, but tend to increase until 150 km depth, reaching up to 50 ppm wt. H2O. The deeper samples are almost dry. Piston-cylinder experiments on hydrogen diffusion between a volatile-rich kimberlitic melt and forsterite suggest that the presence of CO2 in the system could significantly decrease water fugacity and thus forsterite hydration. These experimental results indicate that the hydrogen contents measured in olivine were acquired during a metasomatic event rather than during xenolith extraction by kimberlites. However, this metasomatism was not followed by remobilization of the cratonic root. In the North Tanzanian Divergence, localities within the rift axis and the volcanic transverse belt (Lashaine and Olmani) show significant differences in microstructures and olivine CPO patterns. In Lashaine, coarse-granular microstructures and orthorhombic to axial-[100] CPO patterns in olivine can be explained by transpressional deformation during the formation of the Mozambique belt, or by the occurrence of a remnant of a cratonic domain embedded within the Mozambique belt. Within the rift axis, porphyroclastic to mylonitic microstructures suggest a recent rift-related deformation accompanied by syn-kinematic melt-rock reactions, and followed by variable annealing. The strong heterogeneity in microstructures and olivine CPO suggests that this deformation was acquired during multiple tectonic events probably linked to episodic magma percolation, separated by quiescence episodes. The axial-[100] patterns in olivine and the oblique fast directions reported by SKS studies are coherent with transtensional deformation within the lithospheric mantle beneath the rift. The peridotites from SE Ethiopia are less recrystallized than the rift-axis Tanzanian peridotites, displaying coarse-porphyroclastic microstructures. Microstructures and orthorhombic CPOs in olivine suggest syn- to post-metasomatic deformation. S-waves polarization anisotropies calculated for these samples cannot explain alone the delay times reported by SKS studies in this part of the East-African Rift

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Simonetti, Antonio Carleton University Dissertation Earth Sciences. « Comparative Nd, Pb, and Sr isotopic study of alkalic complexes from East Africa and India ; implications for mantle source regions, melt dynamics and fluid processes ». Ottawa, 1994.

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Ichiki, Masahiro. « Resistivity Structures of a Subduction Zone and a Seismically Active Area - Some Evidence of Fluid and its Role in the Earth's Crust and the Uppermost Mantle ». 京都大学 (Kyoto University), 1999. http://hdl.handle.net/2433/181956.

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Escario, Perez Sofia. « Flux hydrothermaux dans le manteau lithosphérique : étude expérimentale du processus de serpentinisation ». Thesis, Montpellier, 2018. http://www.theses.fr/2018MONTG030/document.

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L'altération hydrothermale du manteau lithosphérique dans les dorsales médio-océaniques fournit un mécanisme de transfert de chaleur et de masse entre la terre profonde et l'océan recouvrant. Le manteau lithosphérique est constituée de roches ultramafiques, également appelées péridotites. Ils comprennent plus de 70% d'olivine, de pyroxènes associés et de phases minérales mineures. La percolation de l'eau de mer dans le socle ultramafique produit l'altération de l'olivine et des pyroxènes en serpentine par le processus de serpentinisation et il est associé à des réactions d'oxydation et de carbonatation (lorsque le CO2 est présent dans le fluide). Le processus de serpentinisation présente un intérêt particulier pour la production de H2, le stockage du CO2, le développement de la vie et la production de gisements de minerai économiquement intéressants concentrés dans les fumeroles hydrothermaux. La durabilité et l'efficacité des réactions nécessitent la pénétration et le renouvellement des fluides à l'interface fluide-minéral. Les failles et les fractures des détachements océaniques sont les zones hautement perméables qui permettent à l'eau de mer de pénétrer profondément dans le manteau lithosphérique. Cependant, le processus de serpentinisation conduit à la précipitation de minéraux de faible densité qui peuvent remplir le réseau poreux, colmatant les chemins d'écoulement qui peuvent modifier les propriétés hydrodynamiques et la réactivité des roches réagi.Ces travaux de thèse visent à améliorer la compréhension des effets en retour des réactions sur les propriétés hydrodynamique du milieu dans les zones hautement perméables au cours des premières étapes de l'altération du socle ultramafique. Il se concentre en particulier sur les changements de texture et les réactions chimiques des roches ultramafiques en évaluant les effets du (i) débit et (ii) des fluides salins riches en CO2. Deux séries d'expériences de percolation réactive ont été réalisées à T = 170-190°C et P = 25MPa. La première série d'expériences consistait à injecter de l'eau de mer dans des échantillonnes de poudre d'olivine compressé sur une large gamme de débits constants. La tomographie par rayons X de haute résolution a été acquise avant et après l'expérience avec des débits élevés; afin d'évaluer les changements dans la microstructure de la roche lors de la réaction de serpentinisation. La deuxième série d'expériences consistait à injecter des fluides salins riches en CO2 dans des échantillonnes de péridotite fracturés mécaniquement.Les résultats ont permis de différencier: (1) un contrôle du débit du flux à l'échelle du pore peut contrôler la composition du fluide local et le développement de différents chemins de réaction à l'échelle de l'échantillon. (2) Le développement de différentes chemins réactifs et les changements de texture dans la roche dépend de la concentration de CO2 dissous dans la solution. (3) La formation de minéraux carbonatés (MgCO3) peut stocker du CO2 sous forme stable de minéral à long terme. (4) Un contrôle de la concentration de CO2 dissous dans le fluide et du réseau de fractures peut améliorer / limiter l'efficacité du stockage de CO2 dans les réservoirs de péridotite fracturés.Ces nouvelles données suggèrent un contrôle complexe de la structure des roches ultramafiques dans le processus de serpentinisation et fournissent de nouvelles perspectives pour le stockage potentiel du CO2 dans les réservoirs fracturés à la péridotite
The hydrothermal alteration of the mantle lithosphere at mid-ocean ridges provides a mechanism for transferring heat and mass between the deep Earth and the overlaying ocean. The mantle lithosphere is constituted by ultramafic rocks, also called Peridotites. They comprise more than 70% of olivine, associated pyroxenes and minor mineral phases. The percolation of seawater into the ultramafic basement produces the alteration of olivine and pyroxenes to serpentine through the so-called serpentinization process and is associated to oxidation and carbonation reactions, the later when CO2 is present. The serpentinization process has special interest on H2 production, CO2 storage, development of life, and the production of economically valuable ore-deposits concentrated at hydrothermal vents. The sustainability and efficiency of the reactions requires penetration and renewal of fluids at the mineral-fluid interface. Oceanic detachment faults and fractures are the highly permeable zones allowing seawater derived fluids to penetrate deeply into the mantle lithosphere. However, the serpentinization process lead to the precipitation of low density minerals that can fill the porous network, clogging flow paths efficiently that may in turn modify the hydrodynamic properties and the reactivity of the reacted rocks.This PhD thesis aims at better understanding the feedback effects of chemical reactions on the hydrodynamic rock properties occurred on highly permeable zones during the earliest stages of alteration of the ultramafic basement. It focuses in particular on the changes in texture and chemical reaction paths of ultramafic rocks by assessing the effects of (i) flow rate and (ii) CO2-rich saline fluids. Two suite of reactive percolation experiments were performed at T=170-190°C and P=25MPa. The first suite of experiments consisted in injecting artificial seawater into porous compressed olivine powder cores over a wide range of constant flow rates. X-Ray µ-tomography of high resolution was acquired before and after the experiment run with high flow rates; in order to evaluate the micro-structural changes of the rock occurred during the serpentinization reaction. The second suite of experiments consisted in injecting CO2-rich saline fluids into peridotite cores mechanically fractured.The results allowed us to differentiate: (1) That, a control of flow infiltration rate at the pore-scale can control the local fluid compositions and the development of different reaction paths at the sample-scale. (2) The development of different reaction paths and textural changes in the rock depends on the concentration of CO2 dissolved in solution. (3) The formation of carbonate minerals (MgCO3) can store CO2 in a form of stable mineral at long-term. (4) A control of the concentration of dissolved CO2(g) and the fracture network can enhance/limit the efficiency of CO2-storage in peridotite fractured reservoirs.These new supporting data suggest a complex control of the structure of the ultramafic rocks in serpentinization process and provides new insights for the potential CO2-storage in peridotite fractured reservoirs

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Hinderer, Jacques. « Sur quelques effets en rotation et deformation d'une planete a noyau liquide, manteau elastique et couche fluide superficielle ». Université Louis Pasteur (Strasbourg) (1971-2008), 1987. http://www.theses.fr/1987STR13172.

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Les equations de base reposant sur la conservation du momenbt cinetique sont developpees pour un modele planetaire possedant un noyau liquide, un manteau deformable elastiquement et une couche fluide superficielle mince. Role oue par les conditions aux limites qui resultant des mouvements dans les parties fluides. Les modes d'oscillation libre et les phenomenes de resonance associes font l'objet d'une etude detaillee: theorie et observations. Differents mecanismes d'excitation de la rotation terrestre prenant en compte dans les parties fluides des mouvements de nature geostrophique ou a tourbillon uniforme. Formulation des solutions en rotation , notamment sous l'action des forces de maree luni-solaires

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Gu, Xiaoyan. « Melt-rock interaction signatures in peridotite from sub-continental mantle (French Massif Central) : A trace element, H, Li and δ7Li approach ». Thesis, Université de Lorraine, 2016. http://www.theses.fr/2016LORR0052/document.

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Des xénolites de péridotite provenant de deux localités du sud du Massif Central Français (Allègre et Mont Coupet), émis avec des modes éruptifs différents, ont été étudiés pour définir l’évolution du manteau sous continental et pour étudier le comportement de Li et H lors des réactions fluides roches lors de leur remonté vers la surface. Un ensemble de 6 xénolites représentatifs a été sélectionné pour chaque localité. La description pétrologique et minéralogique de chaque échantillon a été associée à la mesure des compositions chimiques en éléments majeur (par microsonde électronique) et trace (par LA-ICP-MS) des principales phases minéralogiques (Olivine, Pyroxène, Amphibole). La teneur et la composition isotopique du Li ont été mesurées par microsonde ionique (SIMS), et les teneurs en eau par spectroscopie infrarouge à transformée de Fourrier (FTIR) et SIMS dans les pyroxènes et les olivines. Pour les xénolites d’Allègre, les anomalies négatives en HFSE et les rapports LREE/HREE élevés reflètent un métasomatisme lié à des liquides carbonatitiques, succédant à un processus de fusion partielle du manteau lithosphérique. Pour les échantillons du Mont Coupet, Les anomalies négatives en Ti et Nb des Cpx de tous les échantillons et les anomalies négatives de Zr et Hf pour deux échantillons plus fortement métasomatisés (MC38 et MC34) soulignent également un métasomatisme carbonatitique. Les amphiboles des échantillons MC36 et MC53, dont l'origine doit être associée à des fluides de subduction, sont à l’équilibre avec les Cpx coexistant, ce qui indique que le fluide qui a permis leur formation n’a pas enrichi les Cpx en LREE ou LILE. La composition isotopique de des xénolites d’Allègre montre qu’ils ont été affectés par un métasomatisme en au moins deux étapes par des fluides différents. Les teneurs très élevées en Li des Cpx (jusqu'à 50 ppm) et l’enrichissement même modéré des bordures des olivines sont attribués à un apport de Li par diffusion depuis le magma hôte. Par contre, les compositions isotopiques pauvres en 7Li préservées au coeur des Ol (δ7Li jusqu’à -25‰) suggèrent l’existence d’un autre évènement métasomatique ayant affecté les péridotites avant leur remonté vers la surface. En revanche, les minéraux des xénolites de Mont Coupet ont des concentrations en Li similaires à celles du manteau, avec une répartition à l’équilibre entre les minéraux. Cependant les valeurs de δ7Li négatives observées pour les Cpx et Opx de certains échantillons suggèrent une interaction avec un fluide en quantité limitée et une composition isotopique négative. La préservation du fractionnement isotopique du Li entre les pyroxènes et olivines indique que cette interaction a du avoir lieu peu de temps avant l'entrainement des xénolites vers la surface. Les fluides métasomatiques à l’origine des valeurs de δ7Li négatives observées à Allègre et à Mont Coupet sont liés à un environnement de subduction, probablement lié à l'orogenèse varisque dans le cadre régional du FMC. Les teneurs en eau mesurées dans les xénolites d’Allègre vont de 10,6 à 12,4 ppm, des valeurs beaucoup plus faible que celle du manteau source des MORB. Ceci s’explique par une perte d’eau associée au dégazage du magma lors du refroidissement du lac de lave. L’absence de variation cœur-bord montre une distribution de l’eau à l’équilibre entre les xénolites et la lave hôte. A l’inverse, les xénolites du Mont Coupet ont pu conservé leur teneur en eau acquise en profondeur, contrôlée par les processus de fusion partielle qui ont affecté les péridotites. Cependant, l'échantillon MC34, affecté par le métasomatisme carbonatitique, a la plus haute teneur en eau parmi ces xénolites. Inversement, les échantillons MC36 et MC53 qui contiennent des amphiboles, n’ont pas des teneurs en eau élevées, suggérant que l'agent métasomatique responsable de la formation des amphiboles n'a pas enrichi en eau les autres phases de la péridotite
Peridotite xenoliths sampled from two volcanoes erupting in different modes in two localities, Allègre and Mont Coupet, in the southern domain of the French Massif Central (FMC), have been investigated to constrain the evolution of the sub-continental lithospheric mantle beneath the FMC and the behaviors of Li and H during melt-rock reactions. To answer these questions, a set of 6 representative xenoliths was selected for each locality, and described for their mineralogy and petrography. In-situ measurements were then performed for major and trace elements in Ol, Cpx and Amp when existing, via EPMA and LA-ICP-MS respectively, for Li concentrations and isotopic compositions in pyroxenes and Ol (via SIMS), and water concentrations in minerals (via FTIR and SIMS). Negative HFSE anomalies and markedly high LREE/HREE ratios reflect a carbonatite-related metasomatism following an earlier partial melting process in the lithospheric mantle under Allègre. The Ti and Nb negative anomalies in Cpx from all the Mont Coupet samples and Zr-Hf negative anomalies in Cpx from two most strongly metasomatized samples MC38 and MC34 also point to a carbonatite-related mantle metasomatism. Amp in samples MC36 and MC53, whose origin should be associated with fluids from the subducting slab, have equilibrated most of the trace element composition with coexisting Cpx and the modal metasomatism responsible for the Amp genesis haven’t refertilized Cpx in LREE and LILE. Lithium isotope systematics indicates that Allègre xenoliths were overprinted by (at least) a two-stage metasomatism by melts of different origins. Exceptionally high Li concentrations in Cpx (up to 50 ppm by weight) and slightly increased Li contents at Ol rims are ascribed to a diffusive Li uptake from infiltrating melts derived from the host magma. On the other hand, extremely light Li isotopic compositions preserved in Ol cores (with δ7Li as low as -25‰) suggest another metasomatic event prior to xenolith entrainment by the host magma. In contrast, xenoliths from Mont Coupet have Li concentrations in constituent minerals similar to the normal mantle, and display nearly equilibrated inter-mineral Li partitioning and homogeneous intragranular Li distribution in every phase. The negative δ7Li values of Cpx and Opx in some samples were brought by the exchange with a small-volume melt with Li concentration similar to the normal mantle and light Li isotopic compositions. The preservation of inter-mineral large Li isotopic fractionation currently observed in these samples indicates that the percolation of the melt should occur shortly prior to the entrainment of Mont Coupet peridotite xenoliths by the host magmas. The metasomatic agents, accounting for negative δ7Li values in Ol cores in Allègre xenoliths and in Cpx and Opx in some Mont Coupet xenoliths, are related to a subduction environment. In the regional framework of the FMC, the subduction event most likely occurred during the Variscan orogeny. Water content in Allègre xenoliths ranges from 10.6 to 12.4 ppm in weight, much lower than the water content in the MORB source mantle. It implies that water were lost during the degassing of the host magma during slow cooling of the lava lake. No core-rim variations from profile analysis suggest that xenoliths have achieved water diffusive equilibrium with the host magmas. Peridotite xenoliths from Mont Coupet have retained their original water content from the mantle depths. Partial melting has controlled the water content in most samples from Mont Coupet. However, the subsequent carbonatite-related metasomatism has affected the sample MC34, which had the highest water content among the Mont Coupet xenoliths. And the aqueous agent responsible for presence of Amp in samples MC36 and MC53 has not lead to the considerable increase of water content

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Cerpa, Gilvonio Nestor. « Interaction lithosphère-manteau en contexte de subduction 3D. Relations entre déformation de surface et processus profonds ». Thesis, Nice, 2015. http://www.theses.fr/2015NICE4045/document.

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A l'échelle de plusieurs dizaines de millions d'années, un système de subduction implique de grandes déformations de la plaque plongeante assimilée un solide viscoélastique, et du manteau supérieur assimilé à un fluide newtonien. L'objectif de ce travail est de développer une stratégie de couplage solide-fluide appliquée à l'étude de l'interaction lithosphère-asthénosphère. Cette stratégie est basée sur l'utilisation de maillages non-conformes aux interfaces et d'une méthode de domaines fictifs (MDF) pour la résolution du problème fluide. Pour l'efficience des modèles 3D, nous employons une formulation simplifiée de la méthode de domaines fictifs par multiplicateurs de Lagrange. La MDF développée est validée par des comparaisons avec des solutions analytiques qui montrent que la méthode est d'ordre 1. La stratégie de couplage est également validée par la comparaison avec d'autres méthodes de couplage solide-fluide. Une première étude est ensuite menée pour analyser l'influence de certains paramètres rhéologiques et cinématiques sur la dynamique d'une subduction contrôlée par les vitesses des plaques. Cette étude, en 2D, concerne plus spécifiquement le mécanisme de plissement périodique du slab lorsque celui-ci est ancré à 660 km de profondeur. Ce mécanisme induit des variations de pendage du slab générant des variations de l'état de contrainte de la plaque chevauchante. Un intérêt particulier est porté sur l'influence de la viscosité du manteau sur les plissements. Dans ce cadre, nous réalisons une application à la subduction andine
Over the time scale of tens of millions of years, a subduction system involves large deformations of tectonics plates, as one plate sinks into the Earth's mantle. The aim of this work was to develop a soli-fluid coupling method applied to the lithosphere-asthenosphere interaction in the context of subduction zones. Plates were assumed to behave as viscoelastic bodies, while the upper mantle was assimilated to a newtonian fluid. The method developped here is based on the use of non-matching interface meshes and a fictitious domain method (FDM) for the fluid problem. To optimize the computational efficiency of 3D model, we used a simplified version of the Lagrange multipliers fictitious domain method. The developped FDM has been benchmarked with analytical solutions and we showed that this FDM is a first-order method. The coupling method has also been compared to other fluid-solid coupling methods using matching interfaces meshes. A first two-dimensional study was performed in order to evaluate the influence of some rheological and kinematic parameters on the dynamics of a subduction controlled by the velocity of the plates. This study aimed at investigating cyclic slab folding over a rigid 660 km depth transition zone. This folding mechanism induces variations in slab dip that generate variations in the stress state of the overriding plate. We focussed on the influence of the upper mantle viscosity on slab folding. We also applied this model to the Andean subduction zone. Several studies have determined a cyclic variation of the South-American tectonic regime (period of 30-40~Myrs) which may have been related to the slab dip evolution

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Aelbrecht, Denis. « Étude expérimentale de la rectification d'un écoulement alternatif pariétal en milieu tournant et de la turbulence d'une couche d'Ekman oscillante : application aux courants de marée en Manche orientale ». Université Joseph Fourier (Grenoble ; 1971-2015), 1995. http://www.theses.fr/1995GRE10103.

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La rectification d'un ecoulement de fluide homogene force alternativement sur un fond plat horizontal et le long d'une paroi verticale en milieu tournant est etudie experimentalement. On montre comment les echanges de quantites de mouvement entre la couche d'ekman et la couche limite contre la paroi provoquent une interaction non lineaire forte entre les composantes horizontales du courant, qui engendre un courant residuel significatif le long de la paroi. Ce courant laisse la paroi verticale sur sa droite dans le cas d'une rotation correspondant a l'hemisphere nord. Les caracteristiques de ce courant residuel, ou rectifie, sont determinees a l'aide de techniques de visualisation et de mesure velocimetrique. L'evolution parametrique du phenomene est confrontee avec une modelisation theorique de l'ecoulement et avec des simulations numeriques. L'existence d'un courant residuel cotier le long des cotes francaises de la manche orientale rend pertinente l'application de notre etude aux courants de maree de cette region. On etudie ensuite la transition vers la turbulence de la couche d'ekman presente sous l'ecoulement alternatif force. Des reseaux d'ondes d'instabilite peuvent apparaitre, puis interagir si le nombre de reynolds est grand, ou encore se detruire au moment de la renverse du courant. Ces explosions engendrent un melange vertical important. Des mesures de fluctuations des vitesses, realisees au film chaud, confirment les observations. On peut encore envisager d'appliquer ces resultats a la turbulence de fond des courants de maree dans la manche

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Duclos, Pierre-Arnaud. « IMPACTS MORPHO-SÉDIMENTAIRES DE L'EXTRACTION DE GRANULATS MARINS - APPLICATION AU BASSIN ORIENTAL DE LA MANCHE - ». Phd thesis, Université de Rouen, 2012. http://tel.archives-ouvertes.fr/tel-00795475.

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Le bassin oriental de la Manche, correspondant à une mer épicontinentale à régime macrotidal, est soumis au développement croissant de l'activité d'extraction de granulats marins depuis plusieurs décennies. Des impacts sur le paysage sous-marin et sur l'écosystème sont conditionnés par les impacts physiques induits par l'extraction. Dans le cadre d'une gestion intégrée des zones côtières, une bonne connaissance des impacts, de leurs paramètres forçants et des potentiels de restauration est nécessaire. Pour cela deux sites d'extraction aux environnements physiques caractéristiques du bassin oriental de la Manche sont étudiés au large de Dieppe et en Baie de Seine. Sur ce dernier, l'extraction est menée dans un contexte expérimental et suivie durant 3 années, pendant et après extraction, sur un substrat sablograveleux. L'étude se concentre sur trois principaux impacts physiques : (i) un impact hydrologique, direct, lié à la remise en suspension de sédiment et formant un panache turbide à l'arrière de la drague, (ii) un impact morphosédimentaire, direct, généré lors de l'excavation de sédiment au droit de la zone d'extraction, et (iii) un impact morphosédimentaire indirect correspondant aux dépôts des particules du panache turbide à l'intérieur et autour de la zone d'extraction. Le panache turbide, pour lequel une stratégie d'étude est proposée, dure environ 2 à 3h avec une dynamique essentiellement passive et soumise à des phénomènes de dispersion, décantation et advection. Les concentrations, la granulométrie et la nature des matières en suspension du panache turbide sont surtout contrôlées par la nature du sédiment extrait et le débit d'aspiration de la DAM (Drague Aspiratrice en Marche). La hauteur d'eau et le régime de houle contrôlent le temps de disparition du panache et la remise en suspension des particules des panaches antérieurs déjà décantés. Les impacts au droit de la zone d'extraction sont concernés par des sillons ou dépressions dont les paramètres morphologiques dépendent du caractère intensif ou extensif de l'extraction. La nature des sédiments dans ces excavations est fonction de la variabilité sédimentaire verticale et du potentiel de comblement (flux sédimentaires). Au droit des zones de dépôts, l'impact morpho-sédimentaire est essentiellement marqué par une augmentation de la proportion des silts et des sables. L'extension des dépôts des sables moyens est potentiellement limitée à 250 m autour de l'extraction alors que celle des silts peut atteindre une distance de 6,5 km. La distance des dépôts est fonction de la dynamique du panache turbide, de la vitesse de chute des particules et des courants. Leur nature est liée à celle des particules remises en suspension par la surverse et par l'élinde sur le fond, donc par la nature du substrat et par la vitesse de la DAM. La restauration morphologique des zones excavées est estimée à 10,5 ans en Baie de Seine, confirmant ce qui est généralement admis dans la littérature pour ce type de fonds. Des recommandations pour les suivis de ces impacts et des outils de gestion (indices et lois de comportement) sont proposés pour appréhender ces effets et les comparer d'un site à l'autre

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Neto, Armando Soares dos Reis. « AnÃlise espaÃo-temporal da vegetaÃÃo do manguezal no rio CearÃ, CearÃ, Brasil ». Universidade Federal do CearÃ, 2013. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=10666.

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Os manguezais estÃo distribuÃdos do extremo norte do Brasil atÃ Laguna, regiÃo costeira sul do paÃs, ocorrendo em estuÃrios, lagoas litorÃneas e canais de marÃ. No estado do CearÃ (02Â46 S), nordeste brasileiro, o clima semi-Ãrido apresenta caracterÃsticas que condicionam o crescimento dos bosques de mangue como a sazonalidade das chuvas e a alta incidÃncia de radiaÃÃo solar. As caracterÃsticas climÃticas favoreceram a escolha pela regiÃo para implementaÃÃo da industria salineira no sÃculo passado, como no caso do complexo estuarino do rio CearÃ, localizado na divisa costeira entre os municÃpios de Fortaleza e Caucaia. O presente estudo descreve e analisa a evoluÃÃo espaÃo-temporal do manguezal do rio CearÃ (Fortaleza-CE), com foco na colonizaÃÃo da vegetaÃÃo tÃpica de mangue em Ãreas de salinas abandonadas. O estudo da paisagem foi realizado atravÃs de tÃcnicas de sensoriamento remoto, uso de fotografias Ãreas e imagens de satÃlites, alÃm de visitas de campo, sendo produzidos e analisados mapas temÃticos dos anos de 1968, 1997 e 2009, estimando-se as Ãreas de manguezais e de salinas para cada ano. Para o ano de 2009, foram estimados 1006,6 ha de manguezais, 165% a mais do que em 1968, apresentando sua maior taxa de crescimento por dÃcada entre 1997 e 2009, de 133,25ha/10anos. No perÃodo estudado de 41 anos uma Ãrea de 395 ha de salinas abandonadas foi colonizada naturalmente por bosques de mangue. Uma descriÃÃo mais detalhada da estrutura desses bosques foi realizada atravÃs do estudo fitossociolÃgico na salina Margarida. Na regiÃo mais prÃxima Ã margem do rio foi encontrado um bosque em um estÃgio de desenvolvimento avanÃado, com dominÃncia de Rhizophora mangle e presenÃa de Avicennia spp., altura mÃdia do bosque 10m, DAP mÃdio 14,06 cm e densidade de 1333,33trocos/ha. Em direÃÃo ao continente, evidenciou-se um bosque em processo de colonizaÃÃo inicial na salina, sendo a espÃcie pioneira Laguncularia racemosa associada Ã outras espÃcies vegetais, Portulaca oleracea (beldroega) e a Batis marÃtima (brejo do mangue). Apesar do crescimento quantitativo dos bosques de mangue foram evidenciados diversos impactos ambientais, que acumulados, ocasionaram desequilÃbrio ambiental e perda qualitativa nos benefÃcios proporcionados pelo manguezal do rio CearÃ. Para evidenciar os bens e serviÃos do ecossistema foi realizada uma anÃlise sistÃmica dos fluxos de matÃria e energia que compÃe o complexo estuarino do rio CearÃ. A relaÃÃo dos fluxos com as atividades humanas estabelecidas no ambiente evidenciaram principalmente uma interferÃncia dos impactos ambientais nos serviÃos ambientais relacionados com os fluxos litorÃneos (construÃÃo de espigÃes e dÃficit de sedimentos na costa), fluxos fluvio-marinhos (salinizaÃÃo do estuÃrio e contaminaÃÃo das Ãguas) e os fluxos de sedimentos e gravitacionais (abandono das salinas, impermeabilizaÃÃo do solo e ocupaÃÃo intensa nas Ãreas de dunas). A partir das evidÃncias da recuperaÃÃo do manguezal em Ãreas de salinas abandonadas no rio CearÃ, pÃe-se em discussÃo as definiÃÃes da resoluÃÃo estadual 02/2002 do COEMA, ao legitimar a conversÃo de Ãreas de salinas e apicum para o estabelecimento da carcinicultura, em detrimento de recuperar e conservar os serviÃos ambientais jÃ disponÃveis no ecossistema manguezal. Uma nova postura de conservaÃÃo do manguezal do rio CearÃ representaria custos de oportunidade maiores em uma receita sustentÃvel do desenvolvimento humano nas regiÃes estuarinas e Ãreas litorÃneas do estado no CearÃ, no Brasil e no mundo. A recuperaÃÃo do manguezal do rio CearÃ sÃ serÃ possÃvel apÃs a mitigaÃÃo dos principais impactos ambientais. Para a gestÃo do manguezal do rio CearÃ propÃe-se um sistema de manejo baseado em zonas de recuperaÃÃo de Ãreas degradadas, zonas de monitoramento da regeneraÃÃo natural dos bosques de mangue e zonas de mÃxima conservaÃÃo.
Mangrove ecosystem occurs in Brazil in estuaries, shore lagoons and marine channels inside land, from the extreme North of the country, to well beyond the Tropic of Capricorn, near Laguna, Braziliansâ south coast. In the CearÃ state (02Â46 S), BrazilÂs northeast region, the climate is semi-arid, with seasonal rains and high reception of solar radiation. In the last few decades the human occupations intensify in Ceara river estuarine complex, and modify the landscape in results of their actions, interfering in the natural development of the mangrove ecosystem. This case study reports a description and an analyses of the temporal-spatial development of the mangrove area in the CearÃ river (Fortaleza â CE), focusing on new colonization areas in abandoned saltworks. It was produced thematic maps estimating the mangrove areas and the saltwork areas in the years of: 1968, 1997, and 2009 using remote sensing techniques. In 2009 the mangrove area was 1006.6 ha, 65% more than in 1968, the growth rate was 133.25 ha/10years between 1997 and 2009. In abandoned saltworks areas it was evidenced 395 ha of new colonized mangroves areas. A fitosociologic study was accomplished to demonstrate the detailed description of the mangrove forest structure. The mangrove forest near the main channel of the CearÃ river is described as fringe, an advance development forest, with dominance of Rhizophora mangle and Avicennia spp., medium height of 10 meters, medium DHB 14,06 cm and density of 1333.33 trunk/ha. Down to the terrestrial environment itÂs evidenced basin mangrove forests, in new mangroveÂs colonization areas. The pioneer specie was Laguncularia racemosa associated with other associated species Portulaca oleracea (beldroega) and Batis marÃtima (brejo do mangue). Although the quantitative increment in mangrove forest areas the environment quality was considered low, due the evidenced of the variety of environmental impacts. To highlight the environment services it was necessary a systemic analysis approach of the flows of energy and matter. The relation between the human activities and the environment fluxes related shows the interference of the environment impacts in the environment services, for example, the shore fluxes (sediment deficit) fluvial-marine flux (estuary salinization and water contamination) and the gravitational fluxes (abandoned saltwork, soil impermeabilization and dense urban occupation in dune areas). Consideration about the state resolution COEMA nÂ 02/2002 were made to discuss the recent flexibilization of Brazilian environmental legislation, in order to provide legal tools to appropriations of mangrove areas to industry exploration, the case of shrimp farms legalization. A new posture in mangrove conservation programs in the CearÃ river would represent higher costs of opportunities in a sustainability receipt of human development in estuary regions and shore areas in the CearÃ state, in Brazil and in the whole world. The CearÃ river recuperation will only be possible after the mitigation of the main environmental impacts. It is recommended to install priority conservation zones, natural regeneration monitoring zones and environment rehabilitation zones, in order to enhance the mangrove management plan.

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Marrec, Pierre. « Dynamics of the carbonate system and air-sea CO2 fluxes in western European shelf waters : a multi-scale approach ». Thesis, Paris 6, 2014. http://www.theses.fr/2014PA066656/document.

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L'augmentation continue des concentrations atmosphériques de CO2 due aux activités anthropogéniques est un des principaux facteurs responsable du changement climatique. De par leur forte propension à stocker ce CO2 anthropogénique, les océans jouent un rôle essentiel dans le cycle global du carbone. La quantification des échanges air-mer de CO2 et de leur variabilité à diverses échelles spatio-temporelles représentent encore aujourd'hui un défi majeur dans l'étude du cycle global du carbone. Alors que les flux air-mer de CO2 sont relativement bien quantifiés en milieu océanique, les études réalisées en milieu marin côtier demeurent insuffisantes au regard de l'importante variabilité spatio-temporelle de ces échanges et de la diversité de ces écosystèmes. L'objectif de cette thèse est de mener une étude approfondie de la dynamique du système des carbonates et des échanges air-mer de CO2 à de multiples échelles spatio-temporelles au sein des écosystèmes contrastés du plateau continental nord-ouest européen. Ces systèmes particulièrement dynamiques d'un point de vue biogéochimique présentent l'avantage d'être représentatifs des principales structures hydrographiques des marges continentales tempérés. A ce jour, les études portant sur la dynamique du CO2 dans les eaux de la partie occidentale du plateau continental nord-ouest européen restent peu nombreuses. Du cycle diurne à une échelle multi-annuelle, d'une station fixe au large de Roscoff au plateau continental nord-ouest européen, et d'échantillons d'eau de mer à des données satellitaires, cette thèse offre un aperçu exhaustif de la complexité de la dynamique du système des carbonates et des flux air-mer de CO2 en milieu côtier
The raise of atmospheric CO2 due to anthropogenic activities is a major driver of the climate change. The ocean plays a key role in the uptake of this anthropogenic CO2. The constraint of air–sea CO2 fluxes and their variability at various time and spatial levels remain a central task in global carbon cycle and climate studies. The contribution of open ocean to this uptake is presently rather well quantified, whereas the role of the coastal ocean to this process remains ambiguous due to the diversity and the high spatio-temporal variability of the CO2 system and air-sea CO2 fluxes in these ecosystems. This PhD thesis investigated the spatial and temporal variability of the CO2 system and air-sea CO2 fluxes in contrasted ecosystems of the north-west European continental shelf. These highly dynamic biogeochemical ecosystems host numerous key hydrographical structures (permanently well-mixed, seasonally stratified, frontal structures, estuarine) of temperate zones, in which the dynamic of the CO2 system were poorly documented. From tidal to multi-annual variability, from a fixed station off Roscoff to the north-west European continental shelf and from seawater samples to satellite data, this PhD thesis provides an integrative overview of the complexity of the CO2 system dynamics in coastal seas and the ongoing challenges to achieve

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Reis, Neto Armando Soares dos. « Análise espaço-temporal da vegetação do manguezal no rio Ceará, Ceará, Brasil ». reponame:Repositório Institucional da UFC, 2013. http://www.repositorio.ufc.br/handle/riufc/16314.

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REIS NETO, Armando Soares dos. Análise espaço-temporal da vegetação do manguezal no rio Ceará, Ceará, Brasil. 2013. 103 f. : Dissertação (mestrado) - Universidade Federal do Ceará, Centro de Ciências, Pró-Reitoria de Pesquisa e Pós-Graduação, Programa de Pós-Graduação em Desenvolvimento e Meio Ambiente, Fortaleza-CE, 2013.
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Mangrove ecosystem occurs in Brazil in estuaries, shore lagoons and marine channels inside land, from the extreme North of the country, to well beyond the Tropic of Capricorn, near Laguna, Brazilians’ south coast. In the Ceará state (02°46 S), Brazil´s northeast region, the climate is semi-arid, with seasonal rains and high reception of solar radiation. In the last few decades the human occupations intensify in Ceara river estuarine complex, and modify the landscape in results of their actions, interfering in the natural development of the mangrove ecosystem. This case study reports a description and an analyses of the temporal-spatial development of the mangrove area in the Ceará river (Fortaleza – CE), focusing on new colonization areas in abandoned saltworks. It was produced thematic maps estimating the mangrove areas and the saltwork areas in the years of: 1968, 1997, and 2009 using remote sensing techniques. In 2009 the mangrove area was 1006.6 ha, 65% more than in 1968, the growth rate was 133.25 ha/10years between 1997 and 2009. In abandoned saltworks areas it was evidenced 395 ha of new colonized mangroves areas. A fitosociologic study was accomplished to demonstrate the detailed description of the mangrove forest structure. The mangrove forest near the main channel of the Ceará river is described as fringe, an advance development forest, with dominance of Rhizophora mangle and Avicennia spp., medium height of 10 meters, medium DHB 14,06 cm and density of 1333.33 trunk/ha. Down to the terrestrial environment it´s evidenced basin mangrove forests, in new mangrove´s colonization areas. The pioneer specie was Laguncularia racemosa associated with other associated species Portulaca oleracea (beldroega) and Batis marítima (brejo do mangue). Although the quantitative increment in mangrove forest areas the environment quality was considered low, due the evidenced of the variety of environmental impacts. To highlight the environment services it was necessary a systemic analysis approach of the flows of energy and matter. The relation between the human activities and the environment fluxes related shows the interference of the environment impacts in the environment services, for example, the shore fluxes (sediment deficit) fluvial-marine flux (estuary salinization and water contamination) and the gravitational fluxes (abandoned saltwork, soil impermeabilization and dense urban occupation in dune areas). Consideration about the state resolution COEMA n° 02/2002 were made to discuss the recent flexibilization of Brazilian environmental legislation, in order to provide legal tools to appropriations of mangrove areas to industry exploration, the case of shrimp farms legalization. A new posture in mangrove conservation programs in the Ceará river would represent higher costs of opportunities in a sustainability receipt of human development in estuary regions and shore areas in the Ceará state, in Brazil and in the whole world. The Ceará river recuperation will only be possible after the mitigation of the main environmental impacts. It is recommended to install priority conservation zones, natural regeneration monitoring zones and environment rehabilitation zones, in order to enhance the mangrove management plan.
Os manguezais estão distribuídos do extremo norte do Brasil até Laguna, região costeira sul do país, ocorrendo em estuários, lagoas litorâneas e canais de maré. No estado do Ceará (02°46 S), nordeste brasileiro, o clima semi-árido apresenta características que condicionam o crescimento dos bosques de mangue como a sazonalidade das chuvas e a alta incidência de radiação solar. As características climáticas favoreceram a escolha pela região para implementação da industria salineira no século passado, como no caso do complexo estuarino do rio Ceará, localizado na divisa costeira entre os municípios de Fortaleza e Caucaia. O presente estudo descreve e analisa a evolução espaço-temporal do manguezal do rio Ceará (Fortaleza-CE), com foco na colonização da vegetação típica de mangue em áreas de salinas abandonadas. O estudo da paisagem foi realizado através de técnicas de sensoriamento remoto, uso de fotografias áreas e imagens de satélites, além de visitas de campo, sendo produzidos e analisados mapas temáticos dos anos de 1968, 1997 e 2009, estimando-se as áreas de manguezais e de salinas para cada ano. Para o ano de 2009, foram estimados 1006,6 ha de manguezais, 165% a mais do que em 1968, apresentando sua maior taxa de crescimento por década entre 1997 e 2009, de 133,25ha/10anos. No período estudado de 41 anos uma área de 395 ha de salinas abandonadas foi colonizada naturalmente por bosques de mangue. Uma descrição mais detalhada da estrutura desses bosques foi realizada através do estudo fitossociológico na salina Margarida. Na região mais próxima à margem do rio foi encontrado um bosque em um estágio de desenvolvimento avançado, com dominância de Rhizophora mangle e presença de Avicennia spp., altura média do bosque 10m, DAP médio 14,06 cm e densidade de 1333,33trocos/ha. Em direção ao continente, evidenciou-se um bosque em processo de colonização inicial na salina, sendo a espécie pioneira Laguncularia racemosa associada à outras espécies vegetais, Portulaca oleracea (beldroega) e a Batis marítima (brejo do mangue). Apesar do crescimento quantitativo dos bosques de mangue foram evidenciados diversos impactos ambientais, que acumulados, ocasionaram desequilíbrio ambiental e perda qualitativa nos benefícios proporcionados pelo manguezal do rio Ceará. Para evidenciar os bens e serviços do ecossistema foi realizada uma análise sistêmica dos fluxos de matéria e energia que compõe o complexo estuarino do rio Ceará. A relação dos fluxos com as atividades humanas estabelecidas no ambiente evidenciaram principalmente uma interferência dos impactos ambientais nos serviços ambientais relacionados com os fluxos litorâneos (construção de espigões e déficit de sedimentos na costa), fluxos fluvio-marinhos (salinização do estuário e contaminação das águas) e os fluxos de sedimentos e gravitacionais (abandono das salinas, impermeabilização do solo e ocupação intensa nas áreas de dunas). A partir das evidências da recuperação do manguezal em áreas de salinas abandonadas no rio Ceará, põe-se em discussão as definições da resolução estadual 02/2002 do COEMA, ao legitimar a conversão de áreas de salinas e apicum para o estabelecimento da carcinicultura, em detrimento de recuperar e conservar os serviços ambientais já disponíveis no ecossistema manguezal. Uma nova postura de conservação do manguezal do rio Ceará representaria custos de oportunidade maiores em uma receita sustentável do desenvolvimento humano nas regiões estuarinas e áreas litorâneas do estado no Ceará, no Brasil e no mundo. A recuperação do manguezal do rio Ceará só será possível após a mitigação dos principais impactos ambientais. Para a gestão do manguezal do rio Ceará propõe-se um sistema de manejo baseado em zonas de recuperação de áreas degradadas, zonas de monitoramento da regeneração natural dos bosques de mangue e zonas de máxima conservação.

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Clesi, Vincent. « Formation de la Terre et de Mars : étude expérimentale et numérique ». Thesis, Clermont-Ferrand 2, 2016. http://www.theses.fr/2016CLF22750/document.

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La formation des noyaux planétaires métalliques est un évènement majeur pour l’évolution des propriétés physico-chimiques des planètes telluriques telles que nous les connaissons aujourd’hui. En effet, l’abondance des éléments sidérophiles (i.e. qui ont des affinités chimiques avec les phases métalliques) dans les manteaux planétaires s’explique par les conditions dans lesquelles se sont séparées les phases métalliques et silicatées. Au premier rang de ces conditions se trouvent la pression, la température et la fugacité d’oxygène. La distribution des éléments dans le noyau et le manteau ne peut en effet s’expliquer que pour un équilibre obtenu dans un océan magmatique profond, donc à haute pression et haute température ; et dans des conditions d’oxydo-réduction variables, dont l’évolution la plus probable est de passer d’un état réduit à un état oxydé. Un autre paramètre important est la présence ou non d’eau dans l’océan magmatique primitif. En effet, nous disposons de plus en plus d’arguments permettant d’expliquer l’arrivée des éléments volatils, notamment l’eau, pendant l’accrétion, à partir de briques élémentaires qui contiennent ces éléments. Si l’eau est présente tout au long de l’accrétion, et donc pendant la ségrégation du noyau, elle peut donc avoir un effet sur ce dernier phénomène. Dans cette hypothèse, nous avons mené des expériences de haute pression et haute température permettant de modéliser expérimentalement la formation du noyau en condition hydratée. Ces expériences nous ont permis de montrer que la présence d’eau a un effet sur l’évolution de l’état d’oxydation des manteaux planétaires. Cette évolution oxydo-réductive nous a permis de contraindre des modèles d’accrétion basés sur un mélange de chondrites EH et CI, qui confirment des modèles construits à partir de données isotopiques. Ces modèles nous ont permis de contraindre les concentrations primitives maximum en eau probables sur Terre (1,2-1,8 % pds.) et sur Mars (2,5-3,5 % pds.). D’autre part, nos avons mis en évidence le caractère lithophile (i.e. qui a des affinités chimiques avec les phases silicatées) de l’hydrogène à haute pression, a contrario de plusieurs études précédentes. De ce fait, la différence entre les concentrations initiales élevées en eau que nous obtenons dans nos modèles d’accrétion et les concentrations en eau estimées sur Terre et sur Mars actuellement (2000 ppm et 200 ppm, respectivement) ne peut pas être expliquée par un réservoir d’hydrogène dans le noyau. Enfin, pour améliorer les modèles de formation du noyau, nous avons mis en évidence, par des modèles numériques, l’effet important de la viscosité de l’océan magmatique sur le taux d’équilibre entre noyaux et manteaux des planètes telluriques. Cela nous mène à ré-évaluer les modèles de formation des planètes telluriques basés sur des résultats expérimentaux à l’équilibre, notamment l’extension maximale de l’océan magmatique. L’évolution de la viscosité de l’océan magmatique a donc un impact important sur la composition finale des noyaux planétaires (par exemple les teneurs en soufre, oxygène ou silicium des noyaux terrestres et martiens)
The formation of the metallic planetary cores is a major event regarding to the evolution of physical and chemical properties of the telluric planets as we know it today. Indeed, the siderophile elements (i.e. which has affinities with metallic phases) abundances in planetary mantles is explained by the conditions of core-mantle segregation. Among these conditions, pressure, temperature and oxygen fugacity are the main ones controlling distribution of the elements between mantle and core. This distribution can only be explained by an equilibrium between metal and silicate obtained in a deep magma ocean, which implies high pressure and high temperature of equilibrium. Moreover, the oxygen fugacity must have varied during core-mantle segregation, in a reduced-to-oxidized path most probably. Another important parameter is whether or not water is present in the primordial magma ocean. Indeed, we now have more and more lines of evidences showing that the volatile elements, especially water, arrived during accretion and therefore during the core-mantle segregation, which means that water can have an effect on the latter phenomenon. Considering this hypothesis, we performed several high pressure-high temperature experiments which allowed us to model the formation of the core under hydrous conditions. These experiments demonstrated that water has a significant effect on the redox state evolution of planetary mantles. We use this redox evolution to constrain models of planetary accretions, based on a mix of EH and CI chondrites, showing a good agreement with models based on isotopic data. The output of these models is the maximum initial concentration in water on the Earth (1.2 -1.8 %wt) and on Mars (2.5-3.5 %wt). Furthermore, these experiments showed a lithophile behavior (i.e. which has affinities with silicated phases) of hydrogen at high pressures, contrary to previous studies. Therefore, the difference between high initial concentrations in water yielded by our accretion models and the estimated actual concentrations on the Earth and Mars (2000 ppm and 200 ppm, respectively) cannot be explained by a hydrogen reservoir in the core. Finally, to improve the models of core-mantle segregation, we showed by numerical simulations the important effect of the magma ocean viscosity on the equilibrium between planetary mantles and cores. it lead us to reevaluate the models of accretion based on experimental data, especially the maximum extent of magma oceans. The evolution of the magma ocean viscosity has therefore significant implications on the final composition of planetary cores (for instance on the sulfur, oxygen and silicon content of the Earth’s and Mars’ core)

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Ikhennicheu, Maria. « Étude expérimentale de la turbulence dans les zones à forts courants et de son impact sur les hydroliennes ». Thesis, Lille 1, 2019. http://www.theses.fr/2019LIL1I055/document.

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Les eaux françaises présentent un fort potentiel pour des applications hydroliennes. Dans ces zones à forts courants, d'intenses fluctuations de vitesse sont observées dans la colonne d’eau. Elles proviennent essentiellement des variations bathymétriques du fond marin et peuvent avoir un fort impact sur la production d’énergie et la fatigue des turbines. Afin de comprendre la génération de structures tourbillonnaires dans le sillage d’obstacles et de constituer une base de données pour des études numériques, les conditions rencontrées dans le Raz-Blanchard sont reproduites expérimentalement, dans un bassin à houle et à courant, en similitude de Froude et avec un nombre de Reynolds aussi élevé que possible. Dans cette étude, les variations bathymétriques réelles sont représentées à l'aide d'éléments canoniques : un cube, un cylindre, un plan incliné ou des combinaisons des trois. On distingue alors les variations bathymétriques supérieures à la moyenne (obstacle unique) des cas de rugosités moyennes (combinaison d’obstacles). Afin de caractériser le sillage derrière ces obstacles et d'étudier l’évolution de la turbulence dans la colonne d’eau, des mesures PIV et LDV sont réalisées pour différents taux de turbulence de l'écoulement amont. Les résultats montrent que le cylindre seul produit le sillage le plus étendu. Dans ce cas, de larges structures tourbillonnaires, remontant jusqu’à la surface, sont identifiées. Le développement de méthodes de traitement et d'analyse des données permettent de détecter les centres tourbillonnaires et de déterminer les propriétés de ces tourbillons. L'impact du sillage du cylindre sur le fonctionnement d’une hydrolienne tri-pales à axe horizontal est ensuite étudié. Suivant le positionnement relatif de la turbine par rapport à l'obstacle, l'hydrolienne peut subir de grandes amplitudes de chargements liées aux fluctuations de vitesse engendrées par l'obstacle dans l'écoulement. La mesure des efforts sur les pales et du comportement dynamique de la machine permettent de quantifier ces variations de chargements. Elles dépendent des structures tourbillonnaires impactant la turbine et du cisaillement du profil de vitesse. Ces résultats pourront être exploités pour de futures analyses de fatigue de pales ou autres composantes des hydroliennes
French waters have a strong potential for tidal turbines applications. In these areas of strong currents, intense velocity fluctuations are observed in the water column. They ultimately come from variations in seabed bathymetry and can have a strong impact on tidal turbine energy production and fatigue. In order to understand the turbulent structures generation in the wake of obstacles and to build a data base for future numerical studies, the Alderney Race conditions are reproduced experimentally, in a wave and current tank, in Froude similitude and with a Reynolds number as high as possible. In this study, real bathymetric variations are represented using canonical elements: a cube, a cylinder, an inclined plane or a combination of all three. Cases with bathymetric variations higher than average (obstacle alone) are differentiated from average rugosity cases (obstacles combined). In order to characterize the wake behind these obstacles and to study how turbulence evolve in the water column, PIV and LDV measurements are made for various turbulence rates of the incoming flow. Results show that the cylinder alone produces the most spread out wake. In that case, large scale turbulent structures, rising all the way to the surface, are identified. The development of processing methods and data analysis allows the detection of vortex centres and the determination of their properties. The cylinder wake impact on a tri-bladed horizontal axis turbine behaviour is then studied. Depending on the position of the turbine relative to the obstacle, the turbine can be subject to large amplitude loads due to velocity fluctuations generated by the presence of the obstacle in the flow. Force measurements on the blades and turbine dynamic behaviour characterization allow to quantify those load variations. They depend on the turbulent structures impacting the turbine and the shear in the velocity profile. The results obtained could be exploited for further fatigue analyses on blades or on other tidal turbine components

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Derot, Jonathan. « Utilisation des données de MAREL Carnot pour la compréhension des mécanismes des extrêmes dans la qualité des eaux à Boulogne-sur-Mer ». Thesis, Littoral, 2014. http://www.theses.fr/2014DUNK0375/document.

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L'objectif principal de cette thèse est la caractérisation des dynamiques hautes fréquance en milieu côtier et en particulier leurs extrêmes, par l'intermédiaire de l'étude de série temporelle biogéochimiques à long terme enregistrées par des systèmes automatisés. Les bases de données hautes fréquences utilisées dans cette étude proviennent majoritairement du programme MAREL, qui a été mise en oeuvre par l'IFREMER. Des séries temporelles basses fréquences provenant des programmes de surveillance du littoral SOMLIT (CNRS, INSU) et SRN (Ifremer) sont mises à contribution pour appuyer l'importance des systèmes automatisés. La méthode EMD (Empirical Mode Decomposition) nous a servi de base dans de nombreuses analyses pour étudier ces séries temporelles. Nous avons aussi utilisé des méthodes plus classiques empruntées aux domaines de l'analyse numérique et de la turbulence. Cette études se décompose en 3 parties, et plusieurs annexes. Les matériels et méthodes sont présentés dans la première partie. Dans la seconde partie, la méthode EMD nous a permis de mettre en avant les fortes fluctuations contenues dans les blooms, ainsi que de mener des analyses spectrales grâce à un couplage avec la transformée de Hilbert. L'analyse en composante principale (ACP) a mis en avant les principaux forçages exercés sur la production primaire et les profils de température SOMLIT laissent supposer un impact de la stratification sur l'intensité des blooms. Dans la troisième partie, nous avons mené une étude comparative entre les données basses fréquences et hautes fréquences. Et deux méthodes de cross-corrélation (TDIC et co-spectre) nous ont permis de définir une échelle caractéristique de transition entre les températures de la Manche occidentale et orientale. En annexe, nous avons testé la robustesse de différentes méthodes d'analyses spectrales quant au manque de données dans les séries temporelles, qui est un problème inhérent aux bases de données enregistrées par des systèmes automatisés, et nous avons reproduit un article qui est en cours de soumission
The main objective of this thesis is the characterization of high frequency dynamics in coastal areas and in particular their extremes, through the study of long-term biodeochemical time series registered by automated systems. The majority of high-frequency data sets used in this study came from MAREL program. The low-frequency time series from coastal monitoring programs SOMLIT (CNRS, INSU) and SRN (Ifremer) are employed to support the importance of automated systems. The EMD (Empirical Mode decomposition) method has provided a basis for us to study several of these time series. We also have used some methods more classical borrowed from numerical analysis field and turbulence. This study is organized in three chapters, and several appendices. The first chapter is devoted to the material and method. In the second chapter, using the EMD method we have highlighted the strong fluctuations contained in the blooms, and we have performed spectral analyzes. The principal component analysis (PCA) highlighted the main forcing exerted on primary production and SOMLIT temperature profiles suggest an impact of stratification on the intensity of blooms. In the third chapter, we conducted a comparative study between low-frequency and high-frequency data. Two cross-correlation methods (TDIC and co-spectra) allowed us to define a characteristic transition scale between the temperatures of the western and eastern English Cahnnel. In appendices we tested the robustness of different spectral analysis methods about the missing data in the time series, which is an underlying problem in the database registered by automated systems, and we reproduce a paper, which is under submission

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Crossingham, Alexandra. « Modelling of diamond precipitation from fluids in the lower mantle ». Thesis, 2012. http://hdl.handle.net/10210/5004.

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Taylor, WR. « The role of C-O-H fluids in upper mantle processes : a theoretical, experimental and spectroscopic study ». Thesis, 1985. https://eprints.utas.edu.au/21835/1/whole_TaylorWayneRobert1986_thesis.pdf.

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Evidence from natural magmas and mantle xenoliths argues that fluids in the system C-0-H exercise important influences on petrogenetic processes in the Earth's upper mantle. In this thesis, experimental, spectroscopic and theoretical constraints are applied to provide the necessary basis for understanding the nature of mantle melting as a function of oxygen fugacity (f02) in the model system "peridotite"-C-0-H. Until very recently, most petrogenetic models were based on the assumption that f02 -conditions in magma source-regions of the upper mantle were relatively oxidised, lying near the f02 defined by the synthetic assemblage fay a li te-magneti te-quartz (FMQ). This was cons is tent with the petrogenetic role inferred for oxidised co2-H20 volatiles and carbonated peridotite. However, if magma generation involving volatile components takes place in a reduced environment, for example at f02's near the synthetic iron-wustite (IW) oxygen buffer - as suggested by intrinsic f02 measurements on mantle-derived minerals - then in the model system "peridotite"-C-0-H, volatiles will be dominantly CH4 > H20 > H2 mixtures and crystalline carbonates will not be stable relative to diamond or graphite. The nature of mantle melts produced under reduced conditions is expected to be very different from melts originating in an oxidised environment. To investigate the role of reduced volatiles in upper mantle processes, a two-fold approach has been pursued. Firstly, a thermodynamic model for supercritical C-0-H fluids under elevated P,T conditions was derived. Available volumetric data for the important species: H20, C02, CO, H2, CH4 and C2H6 were used to calibrate an MRK-type equation of state. Using fugacity coefficients derived from the MRK-equation, the distribution of C-0-H species as a function of P,T and f02 has been determined. Application of this model to fluids incorporated in natural diamond (perhaps the only unequivocal example of upper mantle fluids) suggests that the majority of natural diamonds and coexisting C-0-H fluids were at equilibrium in the mantle under redox conditions near or slightly above f02 = IW. A genetic link between methane-bearing fluids and diamond is indicated. The second approach taken in this study was directed at understanding the nature of mantle melting in the presence of reduced volatile species. Because little is known of the mechanism of reduced volatile interaction with silicate systems, an investigation of the CH4-H2-C2H6 fluid solubility mechanism in aluminosilicate melts was undertaken. Jadeite and sodamelilite composition melts were saturated with a C-H fluid at P = 30 kbar and Fourier transform infrared (FTIR) spectra of the resultant high-P quenched glasses were recorded. FTIR spectra distinguish both oxidised and reduced components dissolved in the melt as predicted from theoretical considerations. Low total carbon concentrations (<2000 ppm) in the quenched glasses coupled with FTIR identification of 0-H species and a shift in Si-0 spectral bands, favour a dissolution mechanism for C-H volatiles that involves formation of 0-H groups together with a reduced silicate network component ("silicon monoxide" unit). Dissolution of the latter component results in reduction in overall O:Si stoichiometry of the melt such that O/Si < 2. The effects of C-0-H fluids on aluminosilicate melt structure are revealed indirectly by movement of liquidus field boundaries, particularly those between enstatite and forsterite. Liquidus phase relations in the system Ne-Fo-Q under conditions of C-H volatile saturation indicate that C-H volatile dissolution increases the activity of non-network aluminium and results in silicate network depolymerisation. This is in agreement with the proposed C-H volatile dissolution mechanism. Recognising that reduced volatiles such as CH4 are important primordial components in fluids degassed at mid-ocean ridges and other environments, an hypothesis for redox-reaction induced partial melting of the upper mantle is presented. This hypothesis relates oxidation of methane-rich fluids, precipitation of diamond/graphite and production of incipient H20-rich melts as the combined effects of interaction of deepseated reduced volatiles with oxidised lithosphere.

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Errico, Jessica Cori. « Oxygen isotope evidence for interaction of Franciscan high-grade blocks in the mantle wedge with sediment derived fluids, Ring Mountain (Tiburon) and Jenner Beach, California ». Thesis, 2012. http://hdl.handle.net/2152/ETD-UT-2012-08-6059.

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Oxygen isotopes and major and trace element geochemistry have been used to evaluate the geochemical and tectonic history of a Franciscan hornblende-amphibolite and a eclogite block from Ring Mountain, Tiburon and three eclogite/blueschist blocks from Jenner Beach, California, all blocks have experienced varying amounts of retrogression. Relative to the presumed basaltic protolith, enrichments in large ion lithophile elements (LILEs) indicate interaction with sediment derived fluids in the retrograde eclogite and retrograde blueschist samples and high Mg, Cr, and Ni in actinolite rind indicate interaction with ultramafic rock. The [delta]¹⁸O values of chlorite from the Ring Mountain hornblende-amphibolite and the eclogite block have a narrow range of [delta]¹⁸O values (+7.7-8.2%₀, n=8) and actinolite from actinolite rind on the eclogite block from Ring Mountain and the blueschist/eclogite blocks from Jenner Beach are (+7.8-8.5%₀, n=5). Chlorite-actinolite geothermometry yields temperatures of 200-280°C for actinolite rind formation. Additionally, the [delta]¹⁸O values of both chlorite and actinolite at these temperatures indicates equilibrium with the measured value of Tiburon serpentinites, (7.6 to 8.1%₀, n = 3 Wenner and Taylor, 1974). Oxygen isotope analyses of garnet mineral separates from the eclogite and hornblende-amphibolite from Ring Mountain have [delta]¹⁸O values of +6.8±0.3%₀ (n=7), and +8.2±0.2%₀ (n=7), respectively. Garnets from the three eclogite/blueschist blocks at Jenner Beach have a [delta]¹⁸O value of +9.8±0.7%₀, (n=23). The difference in [delta]¹⁸O values of garnets between the high-grade blocks is likely due to in situ hydrothermal alteration of the seafloor basalt prior to subduction. The geochemical trends can be explained by a model in which during the early stages of subduction pieces of altered oceanic crust are detached from the downgoing slab and incorporated into the mantle wedge soon after reaching peak eclogite or amphibolite facies conditions. As subduction continues, the hanging wall cools and fluids released from subducted sediments infiltrate the overlying mantle wedge. As the blocks cool they develop a retrograde blueschist facies overprint under relatively static conditions. With cooling of the hanging wall and infiltration of sedimentary fluids, serpentinization induces reaction between the blocks and surrounding mantle wedge and Mg-rich actinolite rind is formed. The blocks are then plucked from the mantle wedge and incorporated into the subduction channel where they flow back to the surface via corner flow.
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Robin, Catherine M. I. « Diapirism on Venus and the Early Earth and The thermal effect of fluid flows in AECL's Tunnel Sealing Experiment ». Thesis, 2010. http://hdl.handle.net/1807/24863.

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Flow instabilities occur at all scales in planetary systems. In this thesis we examine three cases of such instabilities, on three very different length scales. In the first part, we test the idea that Archean granite-greenstone belts (GGBs) form by crustal diapirism, or Rayleigh-Taylor instabilities. GGBs are characterized by large granitic domes (50-100 km in diameter) embedded in narrow keel-shaped greenstones. They are ubiquitous in Archean (> 2.5 Ga) terrains, but rare thereafter. We performed finite element calculations for a visco-elastic, temperature-dependent, non-Newtonian crust under conditions appropriate for the Archean, which show that dense low-viscosity volcanics overlying a felsic basement will overturn diapirically in as little as 10 Ma, displacing as much as 60 % of the volcanics to the lower crust. This surprisingly fast overturn rate suggests that diapiric overturn dominated crustal tectonics in the hot conditions of the Early Earth, becoming less important as the Earth cooled. Moreover, the deposition of large volumes of wet basaltic volcanics to the lower crust may provide the source for the formation of the distinctly Archean granitic rocks which dominate Earth's oldest continents. The second part examines the origin of Venusian coronae, circular volcanic features unique to Venus. Coronae are thought to result from small instabilities (diapirs) from the core-mantle boundary, which are typical of stagnant-lid convection. However, most young coronae are located in a region surrounded by long-lived hotspots, typical of a more active style of mantle convection. Using analogue experiments in corn syrup heated from below, we show that the co-existence of diapirs and long-lived mantle plumes are a direct consequence of the catastrophic overturn of the cold Venusian lithosphere thought to have occurred ~ 700 Ma ago. In the last part we analyze the thermal effect of fluid flow through a full-scale experiment testing clay and concrete tunnel seals in a Deep Geological Repository for nuclear was finite element software, we were able to show that the formation of fissures in the heated chamber between the two seals effectively limited heat flow, and could explain the discrepancy between the predicted and measured temperatures.

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Liu, Weining William. « Plasma sheet dynamics induced by plasma mantle ». Thesis, 1988. http://hdl.handle.net/1911/16164.

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Is the magnetic field in the Earth's magnetotail static? if yes, why? if not, what causes the magnetic field to change and how does it evolve with time? These questions have haunted magnetospheric physicists for the past decade. Although significant progress has been made in this area of research, a consensus still does not exist. This thesis approaches the problem from the most fundamental basis--Faraday's law relating the curl of the electric field to the time variation of the magnetic field. If we can reach an independent theory that relates the electric field to the magnetic field, the whole problem can, at least in principle, be solved. This thesis pursues the problem both physically and mathematically. Our answers to the questions listed at the beginning are: (1) the magnetic field is generally not static; (2) the change is powered by the energy transfer from the solar wind to the magnetosphere, the agent that effects the change is plasma injection from the high-latitude plasma mantle; (3) the time-dependence is closely related to the velocity distribution of the mantle plasma; A decrease of B$\sb{\rm z}$ in the near tail and a flux buildup at the farther end of tail are two primary features of the time evolution; (4) a dense, drifting plasma mantle causes an intensive reconfiguration in the plasma sheet and is likely to lead to plasma sheet instability. The general results of the thesis are supportive of Hones' phenomenological model of the tail evolution (Hones, 1977).

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Ghias, Sanaz. « Numerical studies of flow reversals in mantle convection models / ». 2006. http://proquest.umi.com/pqdweb?index=0&did=1240698991&SrchMode=1&sid=5&Fmt=2&VInst=PROD&VType=PQD&RQT=309&VName=PQD&TS=1194986406&clientId=5220.

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Thesis (M.Sc.)--York University, 2006. Graduate Programme in Earth and Space Science.
Typescript. Includes bibliographical references (leaves 143-152). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://proquest.umi.com/pqdweb?index=0&did=1240698991&SrchMode=1&sid=5&Fmt=2&VInst=PROD&VType=PQD&RQT=309&VName=PQD&TS=1194986406&clientId=5220

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Brandt, Martin Barend Christopher. « Imaging the African superplume - upper mantle, tomography and moment tensor ». Thesis, 2012. http://hdl.handle.net/10539/11988.

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Brandt, Martin B.C. 2011. Imaging the African Superplume – Upper mantle, Tomography and Moment tensor. Ph.D. thesis, Faculty of Science, University of the Witwatersrand, Johannesburg, South Africa. The African Superplume, African Superswell and East African Rift System are amongst the most prominent geophysical features on Earth, but the structure, evolution and interaction between these features is controversial. In my thesis I conducted a range of investigations in an effort to better understand these issues. The thesis presents the investigations into the structure and expressions of these features. These include: (I) A study of the upper mantle shear velocity structure beneath southern Africa to investigate the source of the buoyancy that has powered the Superswell; (II) Statistical hypothesis testing of middle-mantle shear velocity tomographic models to evaluate evidence for links between the Superplume and low velocity features in/near the transition zone; and (III) Computation of three new regional moment tensors for South Africa to assess crustal stress in the Kalahari craton, and its link with mantle structure and dynamics. Waveform data were obtained for the study on the upper mantle shear velocity structure and the moment tensor inversions from the Southern African Seismic Experiment Kaapvaal craton array. For the statistical hypothesis testing on global tomography images, new travel-time data from both global and AfricaArray stations were added to Grand’s global shear velocity data set. The principal findings of this study are summarized below. I. The upper mantle shear velocity structure beneath the Kalahari craton is similar to that of other shields, except for slightly slower velocities from 110–220 km depth. The difference may be due to higher temperatures or a decrease in magnesium number (Mg#). If the slower velocities in the deep lithosphere are due solely to a temperature anomaly, then slightly less than half of the unusually high elevation of the Kalahari craton can be explained by shallow buoyancy from a depleted hot lithosphere. Decreasing the Mg# of the lower lithosphere would increase density and counteract higher temperatures. If an excess temperature of 90 K over a 110 km depth range and a corresponding decrease in Mg# of -2 between the Kalahari and the other cratons are assumed, this would match the seismic velocity difference but would result in essentially no buoyancy difference. We conclude that the high elevation of the Kalahari craton can only be partially supported by shallow mantle buoyancy and must have a deeper source. We determined a thickness of 250±30 km for the mantle transition zone below eastern southern Africa, which is similar to the global average, but the corresponding velocity gradient is less steep than in standard global models (PREM and IASP91). Velocity jumps of 0.16±0.1 km/s (eastern) and 0.21±0.1 km/s (central) across the 410 km discontinuity were found. Our results indicate a thermal or chemical anomaly in the mantle transition zone, but this cannot be quantified due to uncertainty. II. Statistical hypothesis testing on our global tomography images indicated that the African Superplume rises from the core-mantle boundary to at least 1150 km depth, and the upper mantle slow-velocity anomaly extends from the base of the lithosphere to below the mantle transition zone. The model that links the African Superplume with the slow-velocity anomaly in the upper mantle under eastern Africa has an equal probability to an alternative hypothesis with a thin slow-velocity “obstruction zone” at 850 to 1000 km depth. III. Finally, we calculated three regional moment tensors for South Africa and made progress towards resolving the discrepancy between the local and moment magnitudes we observe for the region. Moment tensors/focal mechanisms in southern Africa change from normal faulting (extension) in the northeast near the East African Rift to strike-slip faulting in the southwest. This confirms previous studies stating that not only eastern Africa, but also southern Africa is being actively uplifted by lithospheric modification at its base and/or the African Superplume.

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Blatter, Daniel. « Constraining fluid properties in the mantle and crust using Bayesian inversion of electromagnetic data ». Thesis, 2020. https://doi.org/10.7916/d8-b6nw-b545.

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Recent advances in computational power, as well as the hard work of a handful of brilliant scientists, have made Bayesian inversion of geophysical observations possible. This development is highly significant, as it permits the quantification of uncertainty, not only on the inverted model parameters, but also on related properties of interest. This dissertation focuses on the application of a particular kind of Bayesian inversion – trans-dimensional Markov chain Monte Carlo – to electromagnetic data, specifically airborne transient electromagnetic, magnetotelluric, and surface-towed controlled source electromagnetic data. In chapters 2-4, these data, both real and synthetic, are inverted for 1D models of subsurface electrical resistivity. In chapter 5, magnetotelluric data are inverted for 2D models of resistivity – the first time, to the best of my knowledge, that trans-dimensional Bayesian inversion of magnetotelluric data for 2D models has been achieved. In each instance, the uncertainty on bulk resistivity provided by the Bayesian inversion is used to estimate uncertainty on related subsurface properties, including pore fluid resistivity and salinity, porosity, melt fraction, melt volatile content, and bulk mantle volatile inventory. Chapter 1 introduces the topic of Bayesian inversion of electromagnetic data. Chapter 2 concerns trans-dimensional Bayesian inversion of airborne transient electromagnetic data. These data were collected above Taylor Glacier in the McMurdo Dry Valleys region of Antarctica in 2011, and were inverted using deterministic inverse methods to image a conductive channel beneath the glacier, interpreted as a package of brine-saturated sediments. The Bayesian inversion of these data confirms the existence of a conductive channel and provides quantitative uncertainties on the resistivity as a function of depth. These uncertainties are used in conjunction with Archie’s Law to estimate uncertainty on the resistivity of the pore fluids in the sediments. Additionally, the Kullback-Leibler divergence – a statistical measure of the dissimilarity of two distributions – is introduced as a measure of how much influence the observations have on the model parameters as a function of depth. The utility of Bayesian inversion in estimating the noise floor necessary to effectively resolve model structure is demonstrated. In chapter 3, a joint Bayesian framework for inverting electromagnetic data is introduced. A modified version of the algorithm utilized in chapter 2 is applied to jointly invert marine magnetotelluric and surface-towed controlled source electromagnetic data. These data were collected offshore New Jersey in 2015 to image a freshwater aquifer in the continental shelf. Deterministic inversions of this data clearly image a resistive body at depths consistent with low salinity from bore hole measurements collocated with the electromagnetic survey. The Bayesian inversion of this data set again confirms the existence of the resistive region while further providing uncertainty on the inverted resistivity with depth. In some instances, bimodality in the posterior distribution is found, demonstrating the importance of Bayesian inverse methods for fully exploring the model space. The uncertainty on bulk resistivity is used in conjunction with Archie’s Law and the porosity from bore hole measurements in a Monte Carlo framework to estimate uncertainty in the salinity of the pore water as a function of depth for three well locations. These estimates match well with measured salinities at these locations, validating the use of the Bayesian posterior in the context of a Monte Carlo framework to estimate uncertainty on related physical properties. In chapter 4, seafloor magnetotelluric data are again inverted for 1D models of subsurface resistivity, this time to image a conductive channel at the base of the lithosphere. The data are a subset of a deployment of 50 Broadband MT instruments on the seafloor above the Cocos plate offshore Nicaragua. Deterministic inversions of this data revealed a conductive structure at 45-70 km depth, beneath the Cocos plate. This earlier analysis concluded that melt was required at the lithosphere-asthenosphere boundary (LAB) to explain the inverted resistivity, but the deterministic inverse tools available at the time did not permit quantitative uncertainties – on the conductive anomaly itself, the requirement for partial melt, the degree of partial melt, or the degree of mantle hydration. Bayesian inversion of data from two magnetotelluric sites confirm that the conductor is indeed robust, and that melt is required by nearly 100% of the models that fit the data. Further, the resistivity uncertainty from the Bayesian inversion is used in conjunction with petrological modeling of partial melting in the mantle and an estimated probability distribution for temperature to place constraints on the degree of partial melt and mantle volatile (water and carbon) inventory over the depth range 45-63 km. This analysis concludes that large melt fractions and either high temperatures or a high degree of mantle hydration are likely needed to explain the resistivities produced by the Bayesian inversion, potentially explaining the mechanism for plate sliding that enables plate tectonics. Finally, chapter 5 introduces 2D trans-dimensional Bayesian inversion of magnetotelluric data, for the first time to my knowledge. A Gaussian Process-parametrized, trans-dimensional Markov chain Monte Carlo algorithm is used with MARE2DEM to invert synthetic data as well as field data from the Gemini data set from the Gulf of Mexico. For Bayesian inversion to be computationally feasible beyond inverting for 1D models, the cost of forward modeling must be reduced, as well as the number of model parameters that the algorithm must sample over. The first challenge is addressed through high performance computing. The forward modeling is performed on a cluster. In addition, we implement parallel tempering, where multiple Markov chains are run in parallel and swap models at each iteration, vastly increasing the rate at which the model space is explored and sampled. The curse of dimensionality is addressed by utilizing a Machine Learning technique known as a Gaussian Process to represent the model with far fewer parameters than required in a typical discrete finite difference or finite element representation of the subsurface. The Bayesian inversion of the Gemini data successfully recovers the model structure obtained by deterministic inversion of the same data, but additionally provides uncertainty on bulk resistivity. This thesis demonstrates the power and utility of Bayesian inversion to move beyond single estimates of subsurface resistivity. Not only does the work in this dissertation show that Bayesian inversion can provide uncertainty on inverted resistivity, it shows that these inverted uncertainties can be used to place quantitative constraints on parameters related to bulk resistivity. This is crucial to rendering the information obtained from inversion of electromagnetic data useful to disciplines far beyond electromagnetic geophysics.

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Matney, Mark John. « The formation of the Venus ionopause : Interaction between the mantle region and the solar wind ». Thesis, 1990. http://hdl.handle.net/1911/13451.

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The solar wind interacts with the non-magnetic planet Venus by processes within the mantle region, located between the upstream shock and the ionosphere. In this region exospheric neutral atoms from Venus interact with electrons and ions in the moving plasma and modify its flow, resulting in a region of sharp ion density gradients at the boundary between the ionosphere and the mantle called the ionopause. The effect of mass-loading may be simulated by modifying the mass, momentum, and energy conservation equations to include source and loss terms and electromagnetic forces. Using the assumption that the plasma behaves like a fluid, we construct a model to simplify the physics in the mantle. With this model it is possible to generate an oxygen "ledge" in the ion density similar to the observed ionopause. The calculations also show an enhancement in the magnetic field strength above the ionopause as that observed at Venus.

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O'Farrell, Keely Anne. « Comparisons of spherical shell and plane-layer mantle convection models ». Thesis, 2013. http://hdl.handle.net/1807/43693.

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Plane-layer geometry convection models remain useful for modelling planetary mantle dynamics however they yield significantly warmer mean temperatures than spherical shell models. For example, in a uniform property spherical shell with the same radius ratio, f, as the Earth's mantle; a bottom heating Rayleigh number, Ra, of 10^7 and a nondimensional internal heating rate, H, of 23 (arguably Earth-like values) are insufficient to heat the mean temperature, θ, above the mean of the non-dimensional boundary value temperatures (0.5), the temperature in a plane-layer model with no internal heating. This study investigates the impact of this geometrical effect in convection models featuring uniform and stratified viscosity. To address the effect of geometry, heat sinks are implemented to lower the mean temperature in 3D plane-layer isoviscous convection models. Over 100 models are analyzed, and their mean temperatures are used to derive a single equation for predicting θ, as a function of Ra, H and f in spherical and plane-layer systems featuring free-slip surfaces. The inclusion of first-order terrestrial characteristics is introduced to quantitatively assess the influence of system geometry on planetary scale simulations. Again, over 100 models are analyzed featuring a uniform upper mantle viscosity and a lower mantle viscosity that increases by a factor of 30 or 100. An effective Rayleigh number, Raη, is defined based on the average viscosity of the mantle. Equations for the relationship between θ, Raη, and H are derived for convection in a spherical shell with f = 0.547 and plane-layer geometries. These equations can be used to determine the appropriate heating rate for a plane-layer convection model to emulate spherical shell convection mean temperatures for effective Rayleigh numbers comparable to the Earth’s value and greater. Comparing cases with the same H and Raη, the increased lower mantle viscosity amplifies the mismatch in mean temperatures between spherical shell and plane-layer models. These findings emphasize the importance of adjusting heating rates in plane-layer geometry models and have important implications for studying convection with temperature-dependent parameters in plane-layer systems. The findings are particularly relevant to the study of convection in super-Earths where full spherical shell calculations remain intractable.

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Edwards, Stephen John. « Magmatic and fluid processes in the upper mantle : a study of the Bay of Islands ophiolite complex, Newfoundland / ». 1991. http://collections.mun.ca/u?/theses,111984.

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Saka, Yuki. « Analysis of two partial differential equation models in fluid mechanics nonlinear spectral eddy-viscosity model of turbulence and infinite-Prandtl-number model of mantle convection / ». 2007. http://etd.lib.fsu.edu/theses/available/etd-08212007-125009.

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Thesis (Ph. D.)--Florida State University, 2007.
Advisor: Max D. Gunzburger, Florida State University, College of Arts and Sciences, Dept. of Mathematics. Title and description from dissertation home page (viewed Mar. 28, 2008). Document formatted into pages; contains vii, 83 pages. Includes bibliographical references.

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Sieber, Melanie Jutta. « Experimental investigation of the fluid driven carbonation of serpentinites and spinel-peridotites : implications for the carbon and trace element cycle in the forearc region of the mantle wedge ». Phd thesis, 2018. http://hdl.handle.net/1885/158131.

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Significant amounts of carbon (C) are released from the subducting slab into fluids, but less carbon is outgassed in arc volcanoes implying the storage of C in the mantle wedge. This experimental study investigates the fate of C bearing aqueous fluids when they travel through the (partially) hydrated forearc mantle targeting the forearc mantle as a potentially relevant carbon reservoir. Thermodynamic modelling and piston cylinder experiments are utilized to gain a comprehensive understanding on the reaction of slab-derived COH fluids with serpentinites and peridotites between 1-2.5 GPa and 375-750 °C. Powdered, natural serpentinite was used to establish the phase relations of the antigorite-CO2-H2O-system. Cylindrical cores of either natural serpentinite or peridotites are used as starting material investigating the reaction mechanisms, timescales and magnitudes of the CO2-H2O-H2-fluid to rock reaction under realistic grain sizes, natural porosity and given texture. Partitioning coefficients for fluid mobile elements between carbonates and COH-fluids are established experimentally. The results are applied to carbonated high pressure rocks from the Western European Alps. The volatile composition of experimentally derived fluids is quantified in an optimized analytical set up and measurement procedure using gas chromatography. Solids are examined by XRD, Raman spectroscopy, SEM, FE-EPMA, EPMA and Laser-Ablation-ICP-MS. 3D-µ-CT (three dimensional high resolution micro X-ray computed tomography) of recovered rock cores visualizes textures and porosity and determines phase abundances. This study demonstrates that carbonation of the (partially) hydrated forearc mantle efficiently sequesters CO2 from the fluid into newly formed carbonates. With decreasing CO2 activity in the fluid, magnesite is formed with quartz, talc and antigorite at 1-2.5 GPa and 375-650 °C. Above antigorite stability, magnesite is stable with talc, talc+enstatite and enstatite±forsterite. Excess aluminium derived from the consumed serpentine or pyroxenes leads to the formation of chlorite and kyanite. With progressing carbonation and decreasing CO2 activity in the fluid, metasomatic reaction zones of distinct mineral assemblages are formed in core experiments. Reaction zones are fluid permeable because interconnected porosity is created during carbonation of serpentinite and peridotite which likely occurs via an interface coupled dissolution precipitation mechanisms. Carbonation occurs as soon as the COH-fluid is in contact with primary silicates. Carbonation is fast and completed within <1 h of the experiments using powdered serpentinite and within <96 h using serpentinite cores. The carbonation rate of peridotite cores approximates the rate of serpentinite cores. The extent of C sequestering is enhanced when reducing fluids cause additionally graphite precipitation. Fluid mobile elements (e.g. Sr, Ba, Pb) are compatible in carbonates and suitable for monitoring the carbonation process. Carbonation of the partially hydrated forearc mantle is relevant to the cycle of C and trace elements in subduction zones. Over time, the forearc mantle may become a significant reservoir for C contributing to explain the imbalance between carbon released from the slab and carbon output in arc magmatism. Thus, carbonation within the forearc mantle should be considered when estimating carbon fluxes within the Earth’s deep C cycle. Further, a carbonated forearc mantle may host a crustal trace element and isotope signature imposed by metasomatizing fluids liberated from the subducting oceanic crust.

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Pabst, Sonja [Verfasser]. « Investigation of blueschist and serpentinized harzburgite from the Mariana forearc : insights into the mechanisms of element mobilization in subduction zones and storage of fluid mobile elements in the mantle wedge / vorgelegt von Sonja Pabst ». 2009. http://d-nb.info/999509764/34.

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