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1
Alikouss, Saïda. "Contribution a l'étude des fluides crustaux : approche expérimentale et analytique." Vandoeuvre-les-Nancy, INPL, 1993. http://www.theses.fr/1993INPL055N.
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Le développement des techniques d'analyse des inclusions fluides nécessite une calibration précise des installations micro-thermométriques. Une collection d'inclusions fluides synthétiques a été réalisée à partir de systèmes simples (h2o, h2o-co2) et de divers systèmes binaires bien connus (h2o-nacl, h2o-licl, h2o-kcl). Une étude d'inclusions fluides naturelles a été menée afin de caractériser la nature des paléofluides et leur éventuelle contribution à minéralisation en sn-w dans deux sites du limousin: 1) les indices du nord du granite de Saint-Goussaud: des fluides aqueux a h2o-nacl sans aucun composant volatil ont été mis en évidence. Trois groupes de fluides ont été différenciés: des fluides associés à la minéralisation qui traduisent une dilution; des fluides dilués, analogues à ceux de l'episyenisation du massif de St-Sylvestre, traduisant une évolution par condensation à 300 (100) bars; des fluides sales tardifs comparables a ceux associes au dépôt de la pechblende dans le massif de St. Sylvestre; 2) le pipe brechique du Puy-Les-Vignes mis en place au sein de l'unité inferieure des gneiss. Il se distingue du précédent par des fluides très riches en volatiles (co2-ch4-n2-naclh2s. Deux grands stades minéralisateurs ont été identifiés: un stade précoce à tungstene arsenopyrite associé à un fluide à h2o-co2-n2-nacl (ch4) et un stade tardif à sulfures (arsenopyrite, pyrite, chalcopyrite, sphalerite. . . ) Asocial à un fluide a h2o-co2-ch4-nacl(n2). Ces modifications dans la composition du fluide s'accompagnent de modifications des conditions d'oxydo-reduction du milieu qui favorisent le dépôt du minerai
2
Dubois, Michel. "Fluides crustaux : approche expérimentale et analytique : 1) détermination du solvus des systèmes H2O-MCL (M=Li, K, Rb, Cs) et 2) caractérisation et dynamique des fluides des dômes thermiques, sur l'exemple du Diapir Vellave (S-E Massif Central Francais)." Vandoeuvre-les-Nancy, INPL, 1992. http://docnum.univ-lorraine.fr/public/INPL_T_1992_DUBOIS_M.pdf.
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L’étude expérimentale réalisée sur les domaines d'immiscibilité liquide-vapeur des systèmes binaires eau-chlorure alcalin à 500 et 600°C montre une corrélation entre le rayon ionique du cation et la largeur du solvus tandis que la pression critique diminue. Cette étude a nécessité la reconstruction des diagrammes de phase des systèmes H2O-CsCl et H2O-RbCl par une méthode des moindres carrés modifiée. Une étude d'inclusions fluides a été menée sur les différents faciès lithologiques du dôme du Velay (Massif Central Francais). Dans les vaugnerites et les pegmatites associes ont été observés des fluides H2O-CO2-CH4-N2+-H2S. Dans les vaugnerites, ces fluides indiquent des pressions de mise en place trop faible suggérant des modifications post-piégeages. Dans les pegmatites, ces fluides subissent une ébullition à basse pression lors du retour en conditions retromorphiques. Des fluides à CH4-N2+-H2O ont également été retrouvés dans les vaugnerites. Les densités des fluides du métamorphisme (H2O-CO2+-CH4) sont globalement concordantes avec les données geothermobarométriques. Des fluides aqueux de faible salinité ont circulé durant les étapes finales de la mise en place du dôme
3
Eglinger, Aurélien. "Cycle de l'uranium et évolution tectono-métamorphique de la ceinture orogénique Pan-Africaine du Lufilien (Zambie)." Thesis, Université de Lorraine, 2013. http://www.theses.fr/2013LORR0306/document.
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L'uranium, élément lithophile et incompatible, peut être utilisé en traceur géochimique pour discuter des différents modèles de formation et d'évolution de la croûte continentale. Ce travail de thèse, ciblé sur la ceinture Pan-Africaine du Lufilien en Zambie, caractérise le cycle de l'U et les minéralisations d'U pour ce segment de croûte continentale. Les séries silicoclastiques/évaporitiques de la ceinture du Lufilien, encaissant les minéralisations d'U, se sont déposées en contexte de rift (bassin du Roan) lors de la dislocation du supercontinent Rodinia au Néoprotérozoïque inférieur. Les âges U-Pb des grains de zircon détritique de ces séries métasédimentaires soulignent une source principalement Paléoprotérozoïque. Ces mêmes grains de zircon présentent des signatures isotopiques epsilonHf inférieures au CHUR (entre 0 et -15) et des âges modèles TDM Hf, compris entre ~2.9 et 2.5 Ga. Ces données suggèrent donc la formation d'une croûte continentale précoce, et donc une extraction mantellique de l'U dès la fin de l'Archéen puis une remobilisation par déformation et métamorphisme au cours du Protérozoïque. L'U aurait donc été remobilisé et re-concentré au cours d'orogenèses successives jusqu'au cycle Pan-Africain. Durant ce cycle Pan-Africain, la datation U-Pb et la signature REY (REE et Yttrium) des cristaux d'uraninite caractérisent un premier évènement minéralisateur, daté vers 650 Ma, associé à la circulation de fluides de bassin expulsés des évaporites du Roan, circulant à l'interface socle/couverture, dans ce contexte de rift continental. Un second événement minéralisateur, daté vers 530 Ma et contemporain du pic métamorphique, est assuré par des fluides métamorphiques issus de la dissolution des évaporites, en contexte de subduction/accrétion continentale. Quelques remobilisations tardives de l'U sont observées lors de l'exhumation des roches métamorphiquesUranium is an incompatible and lithophile element and can be used as a geochemical tracer to discuss the generation and the evolution of continental crust. This thesis, focused on the Pan-African Lufilian belt in Zambia, characterizes the U cycle for this crustal segment. Silici-clastic and evaporitic sediments have been deposited within an intracontinental rift during the dislocation of the Rodinia supercontinent during the early Neoproterozoic. U-Pb ages on detrital zircon grains in these units indicate a dominant Paleoproterozoic provenance. The same zircon grains show subchondritic epsilonHf (between 0 and -15) and yield Hf model ages between ~2.9 and 2.5 Ga. These data suggest that the continental crust was generated before the end of the Archean associated with U extraction from the mantle. This old crust has been reworked by deformation and metamorphism during the Proterozoic. U has been remobilized and re-concentrated during several orogenic cycles until the Pan-African orogeny. During this Pan-African cycle, U-Pb and REY (REE and Yttrium) signatures of uranium oxides indicate a first mineralizing event at ca. 650 Ma during the continental rifting. This event is related to late diagenesis hydrothermal processes at the basement/cover interface with the circulation of basinal brines linked to evaporites of the Roan. The second stage, dated at 530 Ma, is connected to metamorphic highly saline fluid circulations, synchronous to the metamorphic peak of the Lufilian orogeny. These fluids are derived from the Roan evaporite dissolution. Some late uranium remobilizations are described during exhumation of metamorphic rocks and their tectonic accretion in the internal zone of the Lufilian orogenic belt
4
Ballentine, Christopher John. "He, Ne, and Ar isotopes as tracers in crustal fluids." Thesis, University of Cambridge, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.387053.
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Barker, Shaun, and sbarker@eos ubc ca. "Dynamics of fluid flow and fluid chemistry during crustal shortening." The Australian National University. Research School of Earth Sciences, 2007. http://thesis.anu.edu.au./public/adt-ANU20090711.074630.
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In this thesis, an integrated structural and chemical approach has been used to investigate the spatial and temporal evolution of fluid chemistry, and fluid flow pathways, during crustal shortening. The Taemas Vein Swarm is hosted in a limestone-shale sequence, the Murrumbidgee Group, in the Eastern Belt of the Lachlan Orogen, in New South Wales, Australia. The Taemas Vein Swarm (TVS) is composed of calcite ± quartz veins, hosted in a series of faults and fractures, which extends over an area of approximately 20 km2. The Murrumbidgee Group is composed of several formations, comprising massive grey micritic limestones, redbed sandstones and shales,and thinly interbedded (1020 cm scale) limestones and shales.
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The sedimentary sequence has been folded into a series of upright, open to close
folds, and was probably deformed during either mid-late Devonian, or early Carboniferous, crustal shortening. To the east, the Murrumbidgee Group is overthrust
by a Silurian volcanic sedimentary sequence along the Deakin-Warroo Fault System.
Crosscutting and overprinting relationships demonstrate that vein growth was synchronous with folding, with different vein types related to different fold mechanisms
at various stages of fold growth.
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Flexural slip folding led to the development of bedding-concordant veins (hereafter
called bedding-parallel veins). Flexural flow in semicompetent to incompetent beds
caused en echelon extension vein arrays to grow. Decoupling between beds, and
dilatancy at fold hinges led to significant vein growth. In addition, fold lock-up led to
limb-parallel stretching, and the growth of bedding-orthogonal extension fractures.
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Vein growth is inferred to have occurred in a compressional tectonic regime (i.e.
sigma3=vertical). Oxygen isotope quartz-calcite thermometry suggests that veins formed at temperatures of 100200 oC. The depth of vein formation may have been between
about 5 and 8 km. Vein textures indicate that growth of veins occurred during
multiple cycles of permeability enhancement and destruction. Subhorizontal extension
fractures, and faults at unfavourable angles for reactivation, imply that fluid
pressures exceeded lithostatic levels during the growth of some veins. Coexisting
extension and shear fractures imply that differential stress levels varied over time.
¶
Flexural slip continued throughout folding at Taemas, despite some fold limbs
being at angles extremely unfavourable for reactivation ( > 60). As folds approached
frictional lock-up, flexural slip continued to occur when supralithostatic fluid pressures were developed. Therefore, large, bedding-discordant faults were not
developed to accommodate strain during folding, explaining a deficiency of larger
faults in the TVS.
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Infiltration of overpressured fluids occurred into the base of the Murrumbidgee
Group, and was channelled into a distributed mesh of small faults and fractures.
At the point that a connected backbone flow network developed in the TVS, highpressure
fluids would no longer be available to allow continuing flexural slip on fold
limbs approaching lockup. Thereafter, larger faults would develop, which would
adjust the fault population in the TVS to a more typical displacement-frequency
distribution. This had not occurred in the Taemas area by the time crustal shortening
ceased. An abundance of small faults, and fracturing driven by invasion of
overpressured fluid, implies that the TVS formed via an earthquake swarm process.
¶
Modern analytical techniques, utilising laser ablation sampling technology, allow
high-spatial resolution chemical data to be collected from syntectonic veins. Insights
into the role that fluid-mineral interface processes may have on the chemistry of minerals grown in syntectonic veins were provided by an experimental study. Moderate sized ( < 1−5 mm) synthetic calcite crystals were successfully grown to investigate the uptake of rare earth elements (REE) into calcite. Changes in crystal morphology are linked to variable solution chemistry, which has important implications for the interpretation of hydrothermal vein textures. High-spatial resolution chemical analyses of synthetic calcite crystals demonstrate significant fluctuations in REE concentrations over distances of < 200 μm within calcite crystals. Time-equivalent regions on different crystal faces have significantly different REE concentrations,
indicating that fluctuations in calcite trace element composition cannot be interpreted
exclusively in terms of changing bulk fluid composition. Rare earth element
anomalies (Eu/Eu* and Ce/Ce*) are not significantly influenced by compositional
zoning, and may be robust indicators of changes in solution bulk chemistry and fluid
oxidation state.
¶
Changes in isotopic ratios (13C, 18O and 87Sr/86Sr), and trace element concentrations in veins from the TVS are related to variations in fluid source, flow pathways and chemical conditions (e.g. trace element complexation, precipitation rate, fluid oxidation) during hydrothermal fluid flow. This integrated structural, textural and chemical approach has direct application to the examination of hydrothermal veins
in fracture-hosted ore deposits, and may allow the fluid source and/or chemical
conditions conducive to the formation of high-grade ore to be discerned.
¶
Vein 18O compositions systematically increase upwards through the Murrumbidgee
Group, caused by progressive reaction of an externally derived, low-18O fluid (of
probable meteoric origin) with host limestones. Vein 18O and 87Sr/86Sr compositions vary spatially and temporally within the same outcrop, and within individual veins, which is inferred to be caused by the ascent of packages of fluid along constantly changing flow pathways. Fluid-buffered oxygen isotope ratios at the earliest stages of deformation imply that the TVS formed via an invasion percolation process. Fluid pathways are inferred to have changed constantly, with fractures toggleswitching between high-permeability and low-permeability states, due to repeated
fracture opening and sealing events.
6
Wilkinson, Jamie John. "The origin and evolution of Hercynian crustal fluids, South Cornwall, England." Thesis, University of Southampton, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.252719.
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Siebenaller, Luc Vanderhaeghe Olivier. "Circulations fluides au cours de l'effondrement d'un prisme d'accrétion crustal l'exemple du "Metamorphic Core Complex" de l'île de Naxos (Cyclades, Grèce) /." S. l. : Nancy 1, 2008. http://www.scd.uhp-nancy.fr/docnum/SCD_T_2008_0139_SIEBENALLER.pdf.
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Siebenaller, Luc. "Circulations fluides au cours de l'effondrement d'un prisme d'accrétion crustal : l'exemple du "Metamorphic Core Complex" de l'île de Naxos (Cyclades, Grèce)." Thesis, Nancy 1, 2008. http://www.theses.fr/2008NAN10139/document.
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Cette thèse a pour objectif de caractériser les circulations de fluides en contexte d’effondrement d’un prisme d’accrétion crustal. Le Metamorphic Core Complex (MCC) de Naxos comprend un système de détachement/décollement caractérisé par mylonites, ultramylonites, cataclasites et failles normales dont les relations géométriques témoignent du litage rhéologique de la croûte continentale. La chimie des inclusions fluides déterminée par l’analyse microthermométrique, la spectroscopie RAMAN, l’ablation laser couplée à l’analyse spectroscopique (LA-ICP-MS), le « crush-leach », et les signatures isotopiques C et H des inclusions fluides permettent d’identifier trois grands types de fluides (1) des fluides salés riche en métaux, ii) des fluides aquo-carboniques en équilibre avec les encaissants métamorphiques, et iii) des fluides aqueux, probablement d’origine météorique. Ces données indiquent que la croûte est subdivisée en deux réservoirs séparés par la transition fragile-ductile. Les fluides météoriques circulent en association avec la déformation fragile de la croûte supérieure alors que les fluides salés et les fluides aquo-carboniques circulent en relation avec la déformation ductile. La géométrie de ces réservoirs évolue lors de la formation du MCC, conjointement avec l’exhumation et le refroidissement des roches métamorphiques. Le passage des roches du réservoir ductile au réservoir fragile est associée à un changement depuis un gradient géothermique élevé (60-100°C/km) vers un gradient géothermique plus faible (35-60°C/km). La transition fragile-ductile correspond ainsi à la fois à une limite rhéologique corrélée à une limite thermique et une limite de perméabilitéThe aim of this thesis is to characterize fluid circulations in the context of the collapse of a crustal accretionary belt. The Naxos Metamorphic Core Complex comprises a detachment/decollement system characterized by mylonites, ultramylonites, cataclasites and normal faults with structural relationships reflecting the rheological layering at the crustal scale. Fluid inclusion chemistry is determined by microthermometry, Raman spectroscopy; laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), crush-leach and stable isotopes (C and H) analyses. These data characterize three different types of fluids: (1) high salinity fluids with a high metal content and high Th, (2) aqueous-carbonic fluids in equilibrium with the wall rocks and (3) aqueous probably surface-derived fluids. These data indicate that the crust is subdivided into two crustal reservoirs separated by the brittle/ductile transition. Surface-derived aqueous fluids circulate in association with the brittle deformation within the upper crust whereas aqueous-carbonic and high salinity fluids circulate in relation with ductile deformation. The characteristics of the trapped fluids indicate that as rocks have passed through the ductile/brittle transition they undergo a drastic change in geothermal gradient from 60 to 100°C/km within a lithostatic pressure regime to 35-60°C/km within a hydrostatic pressure regime. This implies that the fluid circulations are closely related to the rheological layering within the crust and its evolution during crustal extension. The ductile/brittle transition corresponds to a rheological boundary correlated to a thermal boundary and impermeable cap
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Blythe, Lara S. "Understanding Crustal Volatiles : Provenance, Processes and Implications." Doctoral thesis, Uppsala universitet, Berggrundsgeologi, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-171486.
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Knowledge of the provenance of crustal volatiles and the processes by which they are released is extremely important for the dynamics of magmatic systems. Presented here are the results of multiple investigations, which aim to understand magmatic volatile contamination from contrasting but complementary perspectives. The main methodologies used include He and C isotope values and CO2/3He ratios of volcanic gases and fluids; simulation of magma-carbonate interaction using high-pressure high-temperature experimental petrology; X-ray microtomography of vesiculated xenoliths and computer modeling. Findings show that the contribution from upper crustal volatiles can be substantial, and is dependant on the upper crustal lithology on which a volcano lies, as well as the composition of the magma supplied. Carbonate dissolution in particular is strongly controlled by the viscosity of the host magma. The details of the breakdown of vesiculated xenoliths is complex but has wide reaching implications, ranging from the dissemination of crustally derived materials through a magma body to highlighting that crustal volatiles are largely unaccounted for in both individual volcano and global volatile budgets. In synthesizing the conclusions from each of the individual perspectives presented, I propose the contribution of volatiles from crustal sources to play a significant role in many geological systems. This volatile component should be taken into consideration in future research efforts.
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Warwick, Alison Julie. "Mineral growth and fluid migration in mid-crustal shear zones." Thesis, University of Plymouth, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.340287.
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Hopkinson, Laurence. "The role of aqueous fluids in crustal processes at the inter and intra-crystalline level." Thesis, University of Southampton, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.296147.
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Tourneur, Enora. "Circulation de fluides aux abords de failles d’échelle crustale : contraintes structurales, microtectoniques, inclusions fluides et géochimiques sur les processus de formation du gisement de Bou Azzer (Ni-Co), Anti-Atlas, Maroc." Thesis, Montpellier, 2019. http://www.theses.fr/2019MONTG064.
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Le district de cobalt-nickel de Bou Azzer est un gisement unique au monde mis en place dans un environnement de serpentinite carbonatée. Deux types de minéralisations sont exploités : des minéralisations massives et un système de veines. Les minéralisations massives sont des corps métalliques, sous forme de lentilles, orientées N120°E et essentiellement enrichies en arséniures de nickel et de cobalt. Elles sont localisées au contact entre une serpentinite, une diorite quartzique ou des roches volcaniques précambriennes. Leur mise en place se fait dans des conditions de moyennes températures (à 220°C en moyenne), de fortes salinités à 38%pds eq. NaCl et de pressions variables entre 67-2883 bars.Les systèmes de veines sont des failles systématiquement minéralisées en arséniures de cobalt et de fer lorsqu’elles recoupent les minéralisations massives. Ces failles recoupent toutes les unités lithologiques de la boutonnière de Bou Azzer, sauf la formation sédimentaire cambrienne. Elles ont des orientations oscillantes entre N/S à N 070°E et sont systématiquement associées à un mouvement normal observé dans le plan vertical. Dans le plan horizontal, les failles minéralisées présentent des jeux sénestres ou dextres cohérents avec un contrôle transtensif selon une direction de raccourcissement orientée N030°E. Le fluide des structures extensives décrit des températures à 170°C en moyenne des salinités entre 32 et 41 %pds eq. NaCl et des pressions variant de 24 et 1800 bars. Les trois types de structures décrivent la même paragenèse minérale, les mêmes textures et les mêmes types de gangues encaissant les minéralisations (quartz et carbonates). Le système évolue de fluides riches en Ni-(Co-Fe) à des fluides riches en Co-(Ni-Fe) depuis les minéralisations massives jusqu’aux systèmes des veines induisant un continuum dans la formation de ces deux types de minéralisations. Deux types de textures sont également observés au sein des minéralisations massives : i) une texture Bréchifiée des Minéralisations Massives (BMM) et une texture Laminée des Minéralisations Massives (LMM). La BMM est illustrée par des arséniures de nickel et de cobalt fracturés par de la serpentine ; par des fragments résiduels de serpentinite, des reliques de spinelles et des fragments d’arséniures de nickel isolés au sein de la gangue carbonatée. La texture de la gangue traduit le fait que ces lentilles minéralisées sont certainement d'anciens corps bréchifiés d’une gangue précoce de serpentinite et des reliques de spinelles. La LMM est décrite par des niveaux alternant entre des arséniures de nickel et de la gangue carbonatée. Cette texture traduit l’architecture précoce du contact faillé sous forme d’anciens lits de spinelles remobilisés par le fluide minéralisateur. Les analyses géochimiques menées sur les arséniures, les gangues carbonatées, les spinelles et le fluide montrent un enrichissement commun en Co, Ni, As, Zn, Bi, Cu, Ag et Au et la même signature en Na/K, Li/B, V/Cr, As/V, Zn/V, Co/Cr. La relation étroite entre ces minéralisations et leurs encaissants indique que le lessivage des structures pré-existantes (spinelles et arséniures de nickel) par un fluide minéralisateur et la précipitation in-situ des métaux sont les processus à l’origine des gisements de cobalt-nickel de Bou Azzer. La formation précoce de la gangue de serpentinites résulterait d’un amincissement crustal en contexte hyper-extensif en transtension décrit il y a 540-560 Ma et accompagné d’un début d’océanisation lors de la formation du complexe supérieur. La circulation d’eau de mer dans le manteau serait l’agent principal de sa serpentinisation. L’exhumation serait le vecteur de la remontée et de la bréchification de la serpentinite mise en contact avec une diorite quartzique. Le timing de formation des minéralisations de Bou Azzer débuterait avec le processus de serpentinisation, décrit pendant les premiers stades de la formation des minéralisationsThe Co-Ni district of Bou Azzer (Anti-Atlas, Morocco) is a unique and particular type of deposit because formed in a context carbonated serpentinite. Two types of mineralisation are exploited: massive orebodies and a system of veins.The massive mineralisations are metallic bodies, in the form of lenses, oriented N120°E and essentially enriched in Ni- and Co-arsenides. They are located at the contact between serpentinite, quartz diorite and Precambrian volcanic rocks. Their formation is realised under medium temperature conditions at ca. 220°C, high salinity at 38% wt eq. NaCl fluids and pressures bracketed between 67-2883 bars.Vein systems are controlled by faults that are systematically mineralised in Co- and Fe- arsenides when they intersect the massive mineralisations. These veins intersect all the lithologic units of the Bou Azzer inlier, except for the Cambrian sedimentary formation. They are trending between NS to N070°E and are systematically associated with normal movements in vertical planes. In the horizontal plane, the mineralised faults present sinistral or dextral motions coherent with a transtensive context controlled by a N030°E shortening direction. Associated fluid yields minimum temperatures of emplacement at 170°C in average, salinity between 32 and 41% wt eq. NaCl and pressures ranging from 24 to 1800 bars.All structures describe a same mineral paragenesis, a same textures and a same type of hosted gangues (quartz and carbonates). Fluids evolve since Ni-(Co-Fe) rich end-members to Co-(Ni-Fe) rich one since massive mineralisations to vein systems inducing a continuum in the formation of both types of mineralisation.Two types of textures are observed in massive mineralisation: a Brecciated Massive Mineralisation (BMM) texture and a Laminated Massive Mineralisation (LMM) one. BMM is characterised by i) Ni-/Co-arsenides fractured by serpentine; ii) residual fragments of serpentinite, iii) spinel relics and iv) fragments of Ni-arsenides isolated within the carbonated gangue. The texture of the gangue reflects the fact that these mineralised lenses are certainly previously formed brecciated bodies of an early gangue of serpentinite and spinel relics. The LMM is described as alternating Ni- arsenides and carbonated gangue layers. The combination of these two textures reflects the early architecture of the faulted contact, i.e. the BMM are ancient brecciated bodies whereas the LMM are witness of ancient mylonitic levels.Geochemical analyses carried out on arsenides, carbonate gangues, spinels and the liquid part of fluid inclusions show a common enrichment in Co, Ni, As, Zn, Bi, Cu, Ag and Au and the same for Na/K, Li/B, V/Cr, As/V, Zn/V, Co/Cr. The close relationship between these mineralisations and their host-rocks indicates that the leaching of pre-existing ultramafic fragments (spinels and Ni-arsenides) by a mineralising fluid and the in-situ metal precipitation are the processes at the origin of the cobalt- Bou Azzer nickel.The early formation of the serpentinite brecciated gangue is interpreted as a result of crustal thinning in a hyper-extensional context that occurred around 540-560 Ma and accompanied by an initiation of oceanic crust formation. The circulation of seawater in the mantle would be the main agent of its serpentinisation. The exhumation would be the vector of the rise and the brecciation of the serpentinite put in contact with a quartz diorite. Consequently, the formation of the Bou Azzer mineralisation would begin with the serpentinisation process, described during the early stages of the mineralisation process and ended by tectonically controlled vein formation
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Ay, Erkan. "Origin of crustal reflectivity and influence of fluids and fractures on velocity at the Kola superdeep borehole." Laramie, Wyo. : University of Wyoming, 2007. http://proquest.umi.com/pqdweb?did=1453231711&sid=4&Fmt=2&clientId=18949&RQT=309&VName=PQD.
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Ricci, Andrea <1989>. "Geochemistry of C-bearing gas compounds in natural fluids under crustal conditions: insights into deep and shallow processes." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2019. http://amsdottorato.unibo.it/9007/1/ricci_andrea_tesi.pdf.
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The PhD research project was aimed to improve the scientific knowledge of the origin and fate of C-bearing gas compounds released from active volcanoes, hydrothermal systems and tectonically active sedimentary basins. The first goal was to investigate the primary source(s) of CH4 and light hydrocarbons in volcanic-hydrothermal gases under crustal conditions. This objective was achieved by comparing the composition of low molecular weight organic fraction (C1-C4) and associated CO2 and H2O in fumarolic gases and geothermal wells from different study areas around the world. We demonstrated that these hydrocarbons derive from biotic sources, i.e., predominantly from the thermal decomposition of organic matter. Meteoric waters and seawater circulating through the crust shuttle organic matter from Earth’s surface into the reservoir rocks. There, high temperature pyrolysis of organic matter and open system degassing generates n-alkanes with isotopic compositions previously classified as being indicative for abiogenesis. These results led us to question the dogma of crustal production of abiotic hydrocarbons and highlighted the potential of n-alkanes to become sensitive indicators of life on habitable (exo)planets. The second goal was to study the secondary processes affecting the composition of CO2, CH4 and light hydrocarbons in natural fluids during their uprising from the deep reservoirs to the surface in different geologic setting, ranging from active volcanoes to sedimentary basins. Under magmatic-hydrothermal conditions, catalytic organic reactions may strongly affect volatile organic compounds, drastically changing alkanes-alkenes-aromatics relative abundances and isotopic composition of C1–C4 hydrocarbons. At peripheral areas of volcanic systems and tectonically active sedimentary basins, composition of CO2 and CH4 in interstitial soil gases and dissolved gases in groundwater are mainly controlled by supergene mechanisms, such as calcite precipitation and microbial-driven processes. These secondary processes likely play a major role in regulating the ultimate release of C-bearing gas compounds into the atmosphere.
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Porritt, R. W., and S. Yoshioka. "Evidence of Dynamic Crustal Deformation in Tohoku, Japan, From Time-Varying Receiver Functions." AMER GEOPHYSICAL UNION, 2017. http://hdl.handle.net/10150/626288.
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Temporal variation of crustal structure is key to our understanding of Earth processes on human timescales. Often, we expect that the most significant structural variations are caused by strong ground shaking associated with large earthquakes, and recent studies seem to confirm this. Here we test the possibility of using P receiver functions (PRF) to isolate structural variations over time. Synthetic receiver function tests indicate that structural variation could produce PRF changes on the same order of magnitude as random noise or contamination by local earthquakes. Nonetheless, we find significant variability in observed receiver functions over time at several stations located in northeastern Honshu. Immediately following the Tohoku-oki earthquake, we observe high PRF variation clustering spatially, especially in two regions near the beginning and end of the rupture plane. Due to the depth sensitivity of PRF and the timescales over which this variability is observed, we infer this effect is primarily due to fluid migration in volcanic regions and shear stress/strength reorganization. While the noise levels in PRF are high for this type of analysis, by sampling small data sets, the computational cost is lower than other methods, such as ambient noise, thereby making PRF a useful tool for estimating temporal variations in crustal structure.
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Fichtel, Katja [Verfasser], Heribert [Akademischer Betreuer] Cypionka, and Ralf [Akademischer Betreuer] Rabus. "Influence of crustal fluids on growth and activity of marine deep biosphere microbial populations / Katja Fichtel. Betreuer: Heribert Cypionka ; Ralf Rabus." Oldenburg : BIS der Universität Oldenburg, 2014. http://d-nb.info/1066873305/34.
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Nüchter, Jens Alexander. "The structural record of mid crustal stress and pore fluid pressure changes related to the earthquake cycle." [S.l.] : [s.n.], 2007. http://deposit.ddb.de/cgi-bin/dokserv?idn=983666849.
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Diop, Catherine Bineta. "Structures et circulations de fluides dans un avant-pays synschisteux : le système de chevauchements des Mauritanides du Sénégal." Vandoeuvre-les-Nancy, INPL, 1996. http://www.theses.fr/1996INPL044N.
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Les Mauritanides du Sénégal (Afrique de l'ouest) sont constituées par des nappes épizonales mises en place au varisque. Ces nappes sont constituées de séries du précambrien supérieur au silurien, répétées dans des duplex caractéristiques des systèmes de chevauchements en rampes et paliers. Les chevauchements sont associés à une schistosité majeure S2 orientée N030°E, 15°NW portant une linéation d'étirement régionalement orientée N130°E. Des critères cinématiques suivant cette linéation indiquent que la mise en place des nappes s'est faite du NW vers le SE. La propagation des nappes vers le SE est accommodée par des structures plicatives variées: antiformes de propagation associées à des kinks, plis déjetés au SE et plis isoclinaux dans les contacts chevauchants, toutes développées dans un même continuum de déformation monocyclique. On observe une deformation cisaillante marquée uniquement au niveau des contacts ; mais dans les nappes, la déformation est à dominante co-axiale, comme le montrent les opr du quartz, qui indiquent une activation des systèmes basal et prismatique . Ces témoins de la déformation plastique sont accompagnés d'une dissolution-cristallisation importante assistée par les fluides et se traduisant par des veines et fentes de tension remplies de quartz, des stylolites et des microfractures indiquant un raccourcissement perpendiculaire à S2. L’étude de la fabrique de forme de marqueurs au sein des nappes a montré une forme généralement aplatie dans la schistosite S2, et compatible avec l'action de la dissolution-cristallisation. Les conditions métamorphiques pendant la formation des nappes déterminée par la pétrologie et l'étude des inclusions fluides ont été estimées entre 500°C et de 300°C du NW au SE pour des pressions maximales de 4 kbars. Les fluides mis en place dans les nappes, principalement aux zones de contact, ont une composition influencée par la nature du substratum. Les Mauritanides sont un avant-pays caractérisé par une tectonique pelliculaire
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Hutnak, Michael. "Heat and fluid flux at a crustal scale : observations and models of coupled transport in young oceanic lithosphere /." Diss., Digital Dissertations Database. Restricted to UC campuses, 2007. http://uclibs.org/PID/11984.
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Wijns, Christopher P. "Exploring conceptual geodynamic models : numerical method and application to tectonics and fluid flow." University of Western Australia. School of Earth and Geographical Sciences, 2005. http://theses.library.uwa.edu.au/adt-WU2005.0068.
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Geodynamic modelling, via computer simulations, offers an easily controllable method for investigating the behaviour of an Earth system and providing feedback to conceptual models of geological evolution. However, most available computer codes have been developed for engineering or hydrological applications, where strains are small and post-failure deformation is not studied. Such codes cannot simultaneously model large deformation and porous fluid flow. To remedy this situation in the face of tectonic modelling, a numerical approach was developed to incorporate porous fluid flow into an existing high-deformation code called Ellipsis. The resulting software, with these twin capabilities, simulates the evolution of highly deformed tectonic regimes where fluid flow is important, such as in mineral provinces. A realistic description of deformation depends on the accurate characterisation of material properties and the laws governing material behaviour. Aside from the development of appropriate physics, it can be a difficult task to find a set of model parameters, including material properties and initial geometries, that can reproduce some conceptual target. In this context, an interactive system for the rapid exploration of model parameter space, and for the evaluation of all model results, replaces the traditional but time-consuming approach of finding a result via trial and error. The visualisation of all solutions in such a search of parameter space, through simple graphical tools, adds a new degree of understanding to the effects of variations in the parameters, the importance of each parameter in controlling a solution, and the degree of coverage of the parameter space. Two final applications of the software code and interactive parameter search illustrate the power of numerical modelling within the feedback loop to field observations. In the first example, vertical rheological contrasts between the upper and lower crust, most easily related to thermal profiles and mineralogy, exert a greater control over the mode of crustal extension than any other parameters. A weak lower crust promotes large fault spacing with high displacements, often overriding initial close fault spacing, to lead eventually to metamorphic core complex formation. In the second case, specifically tied to the history of compressional orogenies in northern Nevada, exploration of model parameters shows that the natural reactivation of early normal faults in the Proterozoic basement, regardless of basement topography or rheological contrasts, would explain the subsequent elevation and gravitationally-induced thrusting of sedimentary layers over the Carlin gold trend, providing pathways and ponding sites for mineral-bearing fluids.
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Moore, Myles Thomas. "Noble Gas and Hydrocarbon Geochemistry of Coalbed Methane Fields from the Illinois Basin." The Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1462561493.
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Salazar, Reinoso Pablo [Verfasser]. "The upper crustal microseismicity image from the North Chilean subduction zone : implications for tectonics and fluid migration / Pablo Salazar Reinoso." Berlin : Freie Universität Berlin, 2011. http://d-nb.info/1025511484/34.
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Blereau, Eleanore Renee. "A Petrochronological Investigation of Metamorphic, Melt and Fluid Related Processes in Lower Crustal Rocks from Southwestern Norway and Southern India." Thesis, Curtin, 2017. http://hdl.handle.net/20.500.11937/59704.
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A petrochronological approach permitted quantitative constraints on the duration, conditions and spatio-temporal controls on metamorphism within complex high-grade metamorphic terranes. The effects of prolonged high temperatures on commonly used geochronometers, zircon and monazite, contrasts between terranes. The availability of these minerals and information recorded in lower crustal rocks is highly controlled by lower crustal processes, but the involvement of particular processes is resolvable through the integration of many analytical techniques into a coherent multidisciplinary interpretation.
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Hood, Shawn Bruce. "Mid-crustal Cu-Au mineralisation during episodic pluton emplacement, hydrothermal fluid flow, and ductile deformation at the Minto deposit, YT, Canada." Thesis, University of British Columbia, 2012. http://hdl.handle.net/2429/42818.
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The genesis of the Minto copper-gold deposit, YT, Canada, has been variously interpreted since its discovery although no existing model accounts for ductile deformation as a control on mineralization. Results from this study show that Minto ore is hosted within ductiley deformed granitoid host rocks emplaced as multiple intrusions into an actively deforming environment, with the variably sheared host rocks separated by incipiently deformed granodiorites essentially barren of mineralisation. Contacts between deformed/mineralized rock and incipiently deformed/barren rock range from abrupt to gradational, and are the product of pre-existing igneous contacts, variably partitioned deformation, or a combination of these. Deformation of granitoids is interpreted to have controlled fluid flow, with associated alteration promoting further deformation and fluid flow. Potassic alteration, in the form of biotite-magnetite, is the dominant alteration associated with mineralisation, and analysis of alteration using isocon diagrams indicates that K, Fe, Si, Cu, Au, and Ag have been added during alteration, although mass has been lost overall due to a relative reduction in Na and Ca. Host rock intrusion, mineralization, and deformation are interpreted via geochronology and crosscutting relationships as ongoing over at least 5 m.a., from about 202 Ma until about 197 Ma, based on U-Pb SHRIMP geochronology of zircons in granitoids and Re-Os ICP-MS geochronology of molybdenite. The trend of mineralisation is now coincident with the strike of foliation on short steep limbs and of axial planes of folded foliation. This geometry may not be representative of original processes, but of remobilization of ore during continued deformation.
The above observations, coupled with data from existing studies, strongly suggest Minto is representative of deposit generation within an arc subduction environment at depths not typically considered for copper-gold deposit formation.
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Maggi, Matteo <1981>. "The role of the fluid phase in the chemico-mechanical evolution of a mid-crustal shear zone: an example from Alpine Corsica." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2011. http://amsdottorato.unibo.it/3773/1/The_role_of_the_fluid_phase_in_the_chemico-mechanical_evolution.pdf.
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Maggi, Matteo <1981>. "The role of the fluid phase in the chemico-mechanical evolution of a mid-crustal shear zone: an example from Alpine Corsica." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2011. http://amsdottorato.unibo.it/3773/.
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Abily, Bénédicte. "Caractéristiques pétrographique, géochimique et structurale de la section crustale profonde de l'ophiolite d'Oman : Implications pour la genèse des magmas et le fonctionnement des chambres magmatiques à l'aplomb d'un centre d'expansion océanique." Phd thesis, Université Paul Sabatier - Toulouse III, 2011. http://tel.archives-ouvertes.fr/tel-00627553.
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Ce travail repose sur (1) une étude de terrain des cumulats lités de l'ophiolite d'Oman, notamment dans plusieurs massifs où cette unité restait largement inexplorée, (2) une étude pétrographique et géochimique (microsonde électronique et LA-ICP-MS) d'environ 700 échantillons et (3) une simulation en laboratoire de la cristallisation de magmas boninitiques en présence d'eau. La cinquantaine de faciès pétrographiques définie, gabbroïques et ultrabasiques, est indispensable pour décrire rigoureusement la croûte profonde omanaise. Cette variété lithologique est révélatrice de la très grande variabilité des paramètres intensifs (P, T°, PH2O ...) et extensifs (composition) lors de la cristallisation des magmas au sein des chambres magmatiques à l'aplomb d'un centre d'expansion océanique. L'orthopyroxène précoce dans les cumulats primitifs (XMg > 80 %) est beaucoup plus commun que ce qui était proposé jusqu'à présent, ce qui remet en cause certaines idées reçues concernant l'origine de l'ophiolite. Je démontre que cette variété lithologique, l'abondance d'orthopyroxène, et d'autres caractéristiques pétrographiques et géochimiques des cumulats d'Oman s'expliquent par le mélange, dans des proportions variables, de deux principaux magmas : un d'affinité tholéiitique issu de la fusion d'une source asthénosphérique " N-MORB ", et un d'affinité andésitique à boninitique issu de la fusion hydratée d'une source lithosphérique déprimée. Ces deux magmas ont circulé dans des chenaux mantelliques (" filons ") avant d'alimenter les chambres. Le rôle de " mélangeur " des chambres magmatiques est ainsi confirmé. La contribution relative de ces deux magmas évolue au cours de l'ascension de diapirs asthénosphériques dans la lithosphère. Des variations abruptes de la pression partielle d'eau sont également indispensables pour rendre compte de l'ensemble de mes observations. Je montre aussi que les failles syn-accrétions, dont l'importance en Oman restait largement sousévaluée, sont un vecteur principal de la pénétration de fluides hydrothermaux jusque dans la croûte profonde en cours de cristallisation. Mon étude me permet également de mieux contraindre l'origine, encore très discutée, des intrusions " wehrlitiques " et de la zone de transition dunitique.
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Barker, Shaun. "Dynamics of fluid flow and fluid chemistry during crustal shortening." Phd thesis, 2007. http://hdl.handle.net/1885/49303.
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In this thesis, an integrated structural and chemical approach has been used to investigate the spatial and temporal evolution of fluid chemistry, and fluid flow pathways, during crustal shortening. The Taemas Vein Swarm is hosted in a limestone-shale sequence, the Murrumbidgee Group, in the Eastern Belt of the Lachlan Orogen, in New South Wales, Australia. The Taemas Vein Swarm (TVS) is composed of calcite ± quartz veins, hosted in a series of faults and fractures, which extends over an area of approximately 20 km2. The Murrumbidgee Group is composed of several formations, comprising massive grey micritic limestones, redbed sandstones and shales,and thinly interbedded (10–20 cm scale) limestones and shales. ¶ ...
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Kay, B. V. "Testing the uncover paradigm: crustal fluid pathways in the Curnamona Province." Thesis, 2017. http://hdl.handle.net/2440/128253.
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This item is only available electronically.In July 2017, scale-reduction was undertaken to improve the bandwidth and resolution of the AusLAMP defined Curnamona Conductor (Robertson et al., 2016) by way of a broadband magnetotelluric profile with site spacing of 2 km, extending from the Erudina Domain across the Mudguard and Quinyambie Domains in the Curnamona Province. A fossil fluid pathway has been identified from the lower mid crustal conductor to the near surface situated near a topographic basement high. The upper crustal conductor has been further delineated beneath the Quinyambie Domain to within 5 km of the surface situated alongside a major crustal feature.
Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Physical Sciences, 2017
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Soeffky, P. "Delineating the deep crustal fluid link between the Paralana Enhanced Geothermal System and the Beverley Uranium Mine using magnetotellurics." Thesis, 2012. http://hdl.handle.net/2440/95486.
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This item is only available electronically.The global demand for clean energy alternatives is constantly increasing, creating significant interest for more sustainable energy resources such as uranium and geothermal. Australia is host to over 25% of the world's known uranium resources as well as having significant geothermal potential. The Mount Painter Domain, in the Northern Flinders Ranges in South Australia, is in a region of anomalously high heat flow generated by radiogenic decay of uranium and thorium rich granites. Two distinct uranium deposits have formed from dissolved uranium carried from the ranges by fluids, being deposited where reduction in sediment pH precipitates uranium. In May 2012 a magnetotelluric profile was collected, extending from the Northern Flinders Ranges to the Lake Frome embayment to help constrain existing resistivity models. Precipitation of uranium at the Beverley Mine site is anomalous as no surface water flow is present, suggesting the presence of subsurface processes. This pathway is linked to a 50m conductive body at the brittle-ductile boundary of the mid-crust, directly under the Paralana geothermal prospect. 3D modelling of the Paralana geothermal prospect suggests deep conductive features connecting with features at the surface.
Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Earth and Environmental Sciences, 2012
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Nüchter, Jens Alexander [Verfasser]. "The structural record of mid crustal stress and pore fluid pressure changes related to the earthquake cycle / Jens Alexander Nüchter." 2007. http://d-nb.info/983666849/34.
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Pastori, Marina. "crustal fracturing field and presence of fluid as revealed by seismic anisotropy: case-histories from seismogenic areas in the Apennines." Thesis, 2011. http://hdl.handle.net/2122/7970.
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During the last decades, the study of seismic anisotropy has provided useful information for the interpretation and evaluation of the stress field and active crustal deformation. Seismic anisotropy can yield valuable information on upper crustal structure, fracture field, and presence of fluid-saturated rocks crossed by shear waves. Several studies worldwide demonstrate that seismic anisotropy is related to stress-aligned, filled-fluid micro-cracks (EDA model, Crampin et al., 1984b; Crampin, 1993).
The seismic anisotropy is an almost ubiquitous property of the Earth and the Shear Wave Splitting is the most unambiguous indicator of anisotropy, but the automatic estimation of the splitting parameters is difficult because the effect of the anisotropy on a seismogram is a second order, not easily detectable effect. Different researchers developed automated techniques aimed to study the Shear Wave Splitting: in this study, the results of different codes are compared in order to evaluate the best method for automatic anisotropy evaluation.
In the last three years, an automatic analysis code, “Anisomat+”, was developed, tested and improved to calculate the anisotropic parameters: fast polarization direction () and delay time (∂t). “Anisomat+” consists of a set of MatLab scripts able to retrieve automatically crustal anisotropy parameters from three-component seismic recordings of local earthquakes. It needs waveforms and hypocentral parameters in the format routinely archived by the Istituto Nazionale di Geofisica e Vulcanologia (INGV).
The code uses horizontal component cross-correlation method: a mathematical algorithm aimed to measure the similarity of the pulse shape between two shear waves.
Anisomat+ has been compared to other two automatic analysis codes (SPY and SHEBA) and tested on three zones of the Apennines (Val d’Agri, Tiber Valley and L’Aquila surroundings). It was observed that, if the number of measures is large enough, at each station the average values of the parameters (fast direction and delay time) are comparable.
The main goal in developing of an automatic code was to have tool able to work on a big amount of data, in a short time, by reducing the errors due to the subjectivity. These two acquirements are very useful and are the basis to develop a quasi real-time monitoring of the anisotropic parameters.
The anisotropic parameters, resulting from the automatic computation, have been interpreted to determine the fracture field geometries; for each area, I defined the dominant fast direction and the intensity of the anisotropy, interpreting these results in the light of the geological and structural setting and of two anisotropic interpretative models, proposed in the literature. In the first one, proposed by Zinke and Zoback (2000), the local stress field and cracks are aligned by tectonics phases and are not necessarily related to the presently active stress field. Therefore the anisotropic parameters variations are only space-dependent. In the second, EDA model (Crampin, 1993), and its development in the APE model (Zatsepin and Crampin, 1995) fluid-filled micro-cracks are aligned or ‘opened’ by the active stress field and the variation of the stress field might be related to the evolution of the pore pressure in time; therefore in this case the variation of the anisotropic parameters are both space- and time- dependent.
I recognized that the average of fast directions, in the three selected areas, are oriented NW-SE, in agreement with the orientation of the active stress field, as suggested by the EDA model, proposed by Crampin (1993), but also, by the proposed by Zinke and Zoback model; in fact, NW-SE direction corresponds also to the strike of the main fault structures in the three study regions. The mean values of the magnitude of the normalized delay time range from 0.005 s/km to 0.007 s/km and to 0.009 s/km, respectively for the L'Aquila (AQU) area, the High Tiber Valley (ATF) and the Val d'Agri (VA), suggesting a 3-4% of crustal anisotropy (Piccinini et al., 2006).
In each area are also examined the spatial and temporal distribution of anisotropic parameters, which lead to some innovative observations, listed below.
o The higher values of normalized delay times have been observed in those zones where most of the seismic events occur. This aspect was further investigated, by evaluating the average seismic rate, in a time period, between years 2005 and 2010, longer than the lapse of time, analyzed in the anisotropic studies. This comparison has highlighted that the value of the normalised delay time is larger where the seismicity rate is higher.
o In the Alto Tiberina Fault area the higher values of normalised delay time are not only related to the presence of a high seismicity rate but also to the presence of a tectonically doubled carbonate succession. Therefore, also the lithology, plays a important role in hosting and preserving the micro-fracture network responsible for the anisotropic field.
o The observed temporal variations of anisotropic parameters, have been observed and related to the fluctuation of pore fluid pressure at depth possibly induced by different mechanisms in the different regions, for instance, changes in the water table level in Val D’Agri (Valoroso et al., GJI submitted), occurrence of the April 6th Mw=6.1 earthquake in L’Aquila (Lucente et al., 2010).
Since these variations have been recognized, it is possible to affirm that the models that better fit my results, both in term of fast directions and of delay times, seems to be those proposed by Crampin (1993) and Zatsepin & Crampin (1995), respectively EDA and APE models.Università degli studi di Perugia
Published
1.11. TTC - Osservazioni e monitoraggio macrosismico del territorio nazionale
3.1. Fisica dei terremoti
3.2. Tettonica attiva
3.8. Geofisica per l'ambiente
open
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Jorge, Raul Carlos Godinho dos Santos 1964. "Caracterização petrográfica, geoquímica e isotópica dos reservatórios metalíferos crustais, dos processos de extração de metais e dos fluidos hidrotermais envolvidos em sistemas mineralizantes híbridos na Faixa Piritosa Ibérica." Doctoral thesis, 2009. http://catalogo.ul.pt/F/?func=item-global&doc_library=ULB01&type=03&doc_number=000571126.
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Tese de doutoramento, Geologia (Metalogenia), 2010, Universidade de Lisboa, Faculdade de CiênciasFundação para a Ciência e Tecnologia. Projectos "ARCHYMEDES" (POCTI/CTA/41393/2001; IR: Fernando J.A.S. Barriga) e "ARCHYMEDES II" (POCTI/CTA/458073/2002; IR: Jorge M.R.S. Relvas); Society of Economic Geologists - BHP Student Research Grant
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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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Hensch, Martin [Verfasser]. "On the interrelation of fluid induced seismicity and crustal deformation at the Columbo submarine volcano (Aegean Sea, Greece) / vorgelegt von Martin Hensch." 2009. http://d-nb.info/1000297624/34.
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PAPESCHI, SAMUELE. "The brittle/ductile transition at upper crustal level: geometry, strain partitioning and fluid circulation. The case study of the Calamita Unit (Elba Island, Northern Apennines, Italy)." Doctoral thesis, 2019. http://hdl.handle.net/2158/1156134.
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This study focuses on the detailed investigation of the brittle/plastic transition in quartz-feldspathic rocks at upper-middle crustal conditions and aims to better understand the role of fluids and temperature during deformation. The Calamita Unit (Elba Island, Italy) is a high metamorphic grade unit (T ~ 650 °C) that has been intruded by a monzogranite body at shallow crustal level (P < 0.2 GPa) and coevally deformed during regional shortening for a limited time span (< 1 Ma). These conditions outline the Calamita Unit as an ideal case study to investigate the brittle/plastic transition at approximately constant pressure (i.e. depth) during temperature decrease, reproducing upper-middle crustal conditions.
The Calamita Schists are a metapsammitic complex exposed in the lower part of the Calamita Unit. Pseudosection modelling and Ti-in-biotite thermometry constrain the peak metamorphic assemblage, marked by andalusite + cordierite + biotite + K-feldspar, at upper amphibolite facies conditions (T ~ 600 – 700 °C; P ~ 0.2 GPa), with microstructures suggesting partial melting. The retrograde path is constrained by chlorite geothermometry in the 300 – 500 °C temperature range.
Detailed field mapping and structural analysis have revealed at map-scale a pattern of heterogeneous deformation characterized by west-dipping high-strain domains localizing eastward-directed deformation interleaved with relatively low-strain domains. In high-strain domains, mylonitic fabrics are, in turn, overprinted in the brittle regime by non-Andersonian subhorizontal faults associated with Riedel shears networks, formed subparallel to C’ shear bands.
Microstructural analysis highlights that temperature decrease and fluid influx controlled the mechanical evolution of the investigated rocks, which are marked by the transition from a high-metamorphic grade foliation to shear bands and mylonites with widespread S-C and S-C’ fabrics, characterized by retrograde, synkinematic white mica and chlorite.
Quartz microfabric displays an evolution from fast grain boundary migration, developed close to peak metamorphic conditions, to subgrain rotation and bulging recrystallization, tracking decreasing temperature during deformation. During decreasing temperature, deformation localized in mylonitic quartz ribbons at amphibolite facies conditions (450 °C < T < 600 °C), where recrystallization was accommodated by dislocation creep of quartz under dominant prism slip, causing the development of strong Y-maximum crystallographic preferred orientations (CPO). Secondary rhomb and acute rhomb slip assisted the recrystallization of grains unfavorably oriented for prism slip, with the activation of slip systems whose misorientation axis lies close to the vorticity axis. At greenschist facies conditions (300 °C < T < 450 °C), deformation localized in phyllonitic domains, producing phase mixing of phyllosilicates and tiny quartz grains. Relic, large quartz grains hardened and fractured along synthetic and conjugate shear bands. The propagation of shear bands occurred under fluid-rich conditions and was controlled by cyclic fracturing and precipitation of new quartz and phyllosilicate grains, deposited by circulating fluids. Precipitated new quartz grains developed a CPO parallel to shear bands controlled by the opening of dilatant sites. The nucleation of fine-grained quartz and ‘soft’ phyllosilicates enhanced strain softening and assisted strain partitioning into localized C’ shear bands at the brittle/plastic transition.
In the brittle regime (T ~ 300 °C), deformation localized on previously formed C’ shear bands, favorably oriented for reactivation, that acted as ductile precursors for misoriented non-Andersonian faults. Brittle deformation in fault zones was controlled by the cyclical interaction between fracturing, taking advantage of weak crystallographic planes in quartz such as the rhombs, and fluid infiltration, assisting the precipitation of new quartz and phyllosilicate grains, lacking a clear preferred orientation.
The data presented in this thesis highlight the role played by fluids during deformation of quartz-feldspathic rocks at the brittle/plastic transition, that efficiently control (1) strain softening of ‘stiff’ domains and (2) strain localization into shear bands that have the potential to act as precursors for non-Andersonian fault zones. The proposed model predicts the development of brittle structures discordantly overprinting ductile fabrics developed in the same kinematic regime, which bears implications for the tectonic evolution of rock volumes (i.e. tectonic units and/or metamorphic complexes) exhumed though the brittle/plastic transition.
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Eckert, Andreas [Verfasser]. "3D multi-scale finite element analysis of the crustal state of stress in the Western US and the Eastern California Shear Zone, and implications for stress - fluid flow interactions for the Coso geothermal field / von Andreas Eckert." 2007. http://d-nb.info/986722170/34.
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