Thèses : « Volatile in magmas »

1

Wayman, Matthew C. « The Transfer of Volatiles Within Interacting Magmas and its Effect on the Magma Mingling Process ». Kent State University Honors College / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=ksuhonors1312924338.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

2

Le, Gall Nolwenn. « Ascension et dégazage des magmas basaltiques : approche expérimentale ». Thesis, Orléans, 2015. http://www.theses.fr/2015ORLE2044/document.

Texte intégral

Résumé :

Afin de parvenir à une meilleure compréhension de la dynamique d’ascension et d’éruption des magmas basaltiques, nous avons réalisé des expériences de décompression à haute pression (200–25 MPa) et haute température (1200°C) spécifiquement orientées pour documenter la nucléation des bulles de gaz ; ce processus, qui constitue la première étape du dégazage magmatique, conditionne l’évolution de la phase gazeuse (force motrice des éruptions explosives) dans le conduit volcanique. Quatre principaux ensembles d’expériences ont été menés afin de mieux comprendre le rôle des volatils majeurs (H2O, CO2, S), ainsi que les effets de la vitesse d’ascension et de la présence de cristaux sur la cinétique de vésiculation (nucléation, croissance, coalescence) des bulles dans les magmas basaltiques. L’objectif est de comprendre les mécanismes qui contrôlent les caractéristiques texturales (nombre, taille, forme des bulles) et chimiques (teneur en volatils dissous, composition des gaz) des produits naturels et de les approcher expérimentalement. Dans ce sens, les verres expérimentaux ont été analysés avant et après décompression sur le plan textural (microtomographie par rayons X, MEB) et chimique (FTIR, microsonde électronique). Nos résultats démontrent une forte influence du CO2 sur les processus ainsi que sur le mode (équilibre vs. déséquilibre) de dégazage des magmas basaltiques, en lien avec des différences de solubilité et de diffusivité entre les espèces volatiles. Nos données, obtenues dans des conditions voisines des conditions naturelles, ont des implications volcanologiques pour l’interprétation des textures de bulles et des mesures de gaz en sortie de conduit, ainsi que, plus spécifiquement, pour la dynamique des éruptions paroxysmales au Stromboli
For a better understanding of the dynamics of ascent and eruption of basaltic magmas, we have performed high pressure (200–25 MPa) and high temperature (1200°C) decompression experiments specifically oriented to document gas bubble nucleation processes. Bubble nucleation occurs first during magma degassing and, so, it is critical to understand bubble nucleation processes to constrain the evolution of the gas phase (which is the driving force of explosive eruptions) in the volcanic conduit. Four main sets of experiments were conducted to better assess the role of the major volatiles (H2O, CO2, S), as well as the effects of ascent rate and crystals, on bubble vesiculation (nucleation, growth, coalescence) kinetics in basaltic magmas. The aim of the study is to understand the mechanisms which control the textural (number, size, shape of bubbles) and the chemical (dissolved volatile concentrations, gas composition) characteristics of natural products, and also to approach them experimentally. In this way, experimental melts, before and after decompression, were analysed texturally (by X-ray microtomography and MEB) and chemically (by FTIR and electron microprobe). Our results demonstrate a strong influence of CO2 on degassing mode (equilibrium vs. disequilibrium) and mechanisms, which are shown to be controlled by differences in solubility and diffusivity between the main volatile species. Finally, our data, obtained under conditions closely approaching natural eruptions, have volcanological implications for the interpretation of bubble textures and gas measurements, as well as, more specifically, for the dynamics of Strombolian paroxysms

Styles APA, Harvard, Vancouver, ISO, etc.

3

Leroy, Clémence. « L'iode et le xénon dans les magmas : deux comportements différents ». Thesis, Paris 6, 2016. http://www.theses.fr/2016PA066094/document.

Texte intégral

Résumé :

La présence de magmas en profondeur permet de contraindre des processus géologiques passés et actuels. Ces magmas (i.e. liquides silicatés) participent aux cycles géochimiques des éléments volatils comme vecteur de matière.Nous étudions deux éléments volatils complémentaires : l'iode (I), un halogène, et le xénon (Xe), un gaz rare. Leur système radioactif éteint 129I/129Xe (T1/2 = 15.7Ma) est utilisé pour dater les processus hadéens et la formation de l'atmosphère, issu de l'évolution d'un océan magmatique. Or on connait peu le comportement de l'iode et du xénon dans les magmas en profondeur à haute pression et température.Notre protocole expérimental vise l'étude de l'incorporation de l'iode et du xénon et de leur solubilité dans les magmas. Pour étudier l'incorporation, la structure des silicates liquides a été caractérisée par diffraction de rayons X avec des expériences in situ réalisées dans des cellules à enclumes de diamant et dans des presses Paris-Édimbourg. Les teneurs de solubilité de l'iode et du xénon ainsi que l'eau ont été mesurés par les méthodes PIXE et ERDA.À hautes pressions, l'iode possède une forte solubilité (quelques %pds) dans les magmas. Les résultats préliminaires sur son incorporation dans du basalte montrent que l'iode ne formerait pas des liaisons covalentes. À haute pression et température (T>300°C - P>1GPa), le xénon forme une liaison covalente Xe-O avec les oxygènes des anneaux de 6 tétraèdres SiO44-. Le xénon a une solubilité élevée dans les magmas (4pds% - 1600°C - 3.5GPa).Les modèles de datation et des cycles géochimiques de l'iode et du xénon doivent être revus en tenant compte de leur comportement différentiel dans les magmas
The presence of magmas at depth helps to constrain past and actual geological processes. Magmas (i.e. silicate melts) participate in geochemical cycles of volatile elements, as vectors of chemical transfers. We study two complementary volatile elements: iodine (I), a halogen, and xenon (Xe), a noble gas. Their extinct 129I/129Xe isotopic system (half-life of 15.7Ma) is used to date Hadean processes and Earth’s atmosphere formation since the atmosphere originated from the Magma Ocean’s evolution. However, little is known about the behavior of both iodine and xenon in silicate melts at depth, under HT and HP conditions. Our experimental protocol aims at elucidating the incorporation process of xenon and iodine in silicate melts, and their solubility. To understand the incorporation of iodine and xenon in magmas, the structure of silicate melts was investigated by in situ diamond anvil cells and Paris-Edinburgh press experiments coupled with X-ray diffraction characterization. Iodine and xenon’s solubility, along with water content are obtained by PIXE and ERDA methods using a nuclear microprobe. At high pressure, iodine has a high solubility (about few wt.%) in magmas. Preliminary results on iodine incorporation in basaltic melt show an absence of covalent bond. At high pressure and temperature conditions (T>300°C – P>1GPa), xenon forms a Xe-O covalent bond with the oxygens of the 6-membered-rings of the melt network. Its solubility in silicate melts is also high (about 4wt.% in haplogranite melts at 1600°C and 3.5GPa). Considering the xenon and iodine differential behavior in melts at depth, a revision of dating models in xenon and iodine cycles must be considered

Styles APA, Harvard, Vancouver, ISO, etc.

4

Johnson, Emily Renee. « Volatiles in basaltic magmas from central Mexico : from subduction to eruption / ». Thesis, Connect to title online (Scholars' Bank) Connect to title online (ProQuest), 2008. http://hdl.handle.net/1794/8331.

Texte intégral

Résumé :

Thesis (Ph. D.)--University of Oregon, 2008.
Typescript. Includes vita and abstract. Includes bibliographical references (leaves 153-167). Also available online in Scholars' Bank; and in ProQuest, free to University of Oregon users.

Styles APA, Harvard, Vancouver, ISO, etc.

5

Hunt, Emma J. « Magma chamber dynamics in the peralkaline magmas of the Kakortokite Series, South Greenland ». Thesis, University of St Andrews, 2015. http://hdl.handle.net/10023/6900.

Texte intégral

Résumé :

Understanding crystallisation in magma chambers is a key challenge for igneous petrology. It is particularly important to understand the origins of layering in peralkaline rocks, e.g. the kakortokite (nepheline syenite), Ilímaussaq Complex, S. Greenland, as these are commonly associated with high value multi-element economic deposits. The kakortokite is a spectacular example of macrorhythmic (>5 m) layering. Each unit consists of three layers comprising arfvedsonite-rich (sodic-amphibole) black kakortokite at the base, grading into eudialyte-rich (sodic-zirconosilicate) red kakortokite, then alkali feldspar- and nepheline-rich white kakortokite. Each unit is numbered -19 to +17 relative to a characteristic well-developed horizon (Unit 0), however there is little consensus on their development. This project applies a multidisciplinary approach through field observations combined with petrography, crystal size distributions (CSDs), mineral and whole rock chemistries on Units 0, -8 to -11 and a phonolite/micro-nephelinolite (“hybrid”) sequence that crosscuts the layered kakortokite. Textures and compositions are laterally consistent across outcrop and indicators of current activity are rare. CSDs indicate in situ crystallisation with gravitational settling as a minor process. Chemical discontinuities occur across unit boundaries. The layering developed through large-scale processes under exceptionally quiescent conditions. The discontinuities reflect open-system behaviour; units were formed by an influx of volatile-rich magma that initiated crystallisation in a bottom layer. Nucleation was initially suppressed by high volatile element concentrations, which decreased to allow for crystallisation of arfvedsonite, followed by eudialyte, then alkali feldspar and nepheline to form each tripartite unit. The chemistry of the hybrid indicates mixing between a primitive (sub-alkaline) magma and kakortokite. Thus injections of magmas of varying compositions occurred, indicating a complex plumbing system below current exposure. The lessons learned at Ilímaussaq, which is extremely well exposed and preserved, are relevant to understanding magma chamber dynamics in the more common instances of pervasively altered peralkaline rocks.

Styles APA, Harvard, Vancouver, ISO, etc.

6

ESPOSITO, ROSARIO. « Geochemical study of the Solchiaro (Procida Island, Campi Flegrei) eruptive products by microthermometry and microanalysis of fluid and melt inclusions ». Doctoral thesis, Università degli Studi di Napoli Federico II, 2010. http://hdl.handle.net/10281/349383.

Texte intégral

Résumé :

In this study is presented the work I have done during the 4 years of a PhD program that was part of the internationalization programme of the Italian research system approved by the Ministero della Ricerca e dell’Università (MIUR) between the Università degli Studi di Napoli “Federico II”, (Dipartimento di Scinze della Terra) and the Virginia Polytechnic Institute and State University (Department of Geosciences). 107 selected MI, 77 open glasses, 80 olivines and 7 bulk rocks (from 4 representative samples of Solchiaro eruption) were analyzed for major/trace element and volatiles. Mostly, olivine compositions vary from Fo82 to Fo88 with one maximum value of Fo90. 2 group of MI were recognized based on major element composition: 1) K2O-rich MI with composition that is the same of bulk rock in the literature and 2) K2O-poor MI that instead have been never reported from previous study of the PVD (Phlegrean Volcanic District). The first group consists of 95% of the melt and relates mostly to within plate setting whereas the second group consists of around 5% of the melt and relates to subduction setting. Magma associated with Solchiaro eruption evolved under open system processes as suggested by petrographic evidence and glass compositions. H2O-CO2 concentrations dissolved in glass suggest that magma was saturated in volatiles at least at 12.5 km depth and continuously degassed during the Solchiaro eruption. Maximum depths are in agreement with other studies based on different approaches. Volatile correlations suggest that during closed system degassing, as the Solchiaro eruption progressed, maximum S contents decreased and minimum Cl and F contents increased. The major, trace and volatile evolution of crystals, glass, and MI is consistent with a model that involves either continuous or episodic recharge of the magma chamber ponded at least at 12.5 km depth

Styles APA, Harvard, Vancouver, ISO, etc.

7

ESPOSITO, ROSARIO. « Studies of volatile evolution in magmatic systems using melt inclusions ». Doctoral thesis, Virginia Polytechnic Institute and State University, 2012. http://hdl.handle.net/10281/349369.

Texte intégral

Résumé :

Understanding volatile evolution associated with active volcanic magmatic systems is of paramount importance because volatiles control and determine the magnitude of an eruption owing to the large change in molar volume that volatile species show depending on their physical state (volatiles dissolved in silicate melts vs. volatiles exsolved as vapor). For active volcanic systems studying the volatile evolution can help to assess the potential hazard associated to a certain locality. Also, volatile evolution in magmatic system controls the formation of certain ore deposits. Despite the importance of understanding volatile evolution of magmatic systems, concentrations of volatiles of evolving magmas are not easily available especially for magmas originated in the deep crust. Fortunately, sample of melts can be entrapped as melt inclusion (MI) into growing igneous minerals in crystalizing magma chamber. After the entrapment, the crystal works as an insulating capsule from the external magmatic environment. Researchers have started to use MI because they provide some advantages in respect to the classical whole rock approach to petrological studies. One of the most important advantages is that MI often represent sample of a deep and non-degassed melt (glass) available at Earth’s surface. This dissertation is a compilation of four publications produced during six years of research and is addressed to give a contribution in understanding the volatile evolution in magmatic systems and also to improve the present understanding of information that can be obtained using the melt inclusions technique. In the first chapter, I present an alternative interpretation of H2O-CO2 trends obtained from MI. In this study, we demonstrate that these trends can be due to post entrapment crystallization on the wall of the MI and not to magma ascent. This alternative view is more realistic especially for cases where in the same phenocrysts MI show strongly different CO2 concentrations. In the second chapter, I present a study to test for the MI reliability in recording volatile concentrations. We used the approach of the melt inclusion assemblage (MIA) that consists of analyzing groups of MI presumably entrapped at the same time and, thus, at same chemical and physical conditions. The results show that most of the MIA studied show consistent volatile concentrations corroborating the reliability of the MI technique. CO2 shows the highest degrees of variability and we have assessed this behavior mostly to C-contamination in the surface of the sample. The third chapter is a study case (the Solchiaro eruption in Southern Italy) that shows the potential uses of MI to understanding the volatile evolution. I present a model showing the dynamic of the magma based on MI. This study also discusses the origin of anomalous MI and which MI provide the best information. The final chapter is dedicated to test the applicability of the new Linkam TS1400XY heating stage. I was able to show how this new microthermometric tool is capable of homogenizing MI at high temperature and to quench MI to a homogeneous glass state

Styles APA, Harvard, Vancouver, ISO, etc.

8

Chamboredon, René. « Caractérisation et origine des magmas alcalins et des fluides sous le massif volcanique du Jbel Saghro, Anti Atlas, Maroc ». Thesis, Montpellier, 2015. http://www.theses.fr/2015MONTS070/document.

Texte intégral

Résumé :

Les laves alcalines sous-saturées riches en éléments volatils sont les marqueurs du rôle important des fluides dans le manteau et des interactions fluide-roche et magma-roche, processus clés pour comprendre la dynamique du manteau convectif et les interactions asthénosphère-lithosphère en domaine intracontinental. L’objectif de cette thèse est d’apporter de nouvelles contraintes sur la genèse des magmas alcalins en caractérisant les conditions de cristallisation, la source et les processus de fusion partielle à l’origine des néphélinites à olivine, des néphélinites à pyroxène et des basanites du champ volcanique du Jbel Saghro dans l’Anti-Atlas marocain. L’étude pétrologique et géochimique des roches et des minéraux, couplée à l’analyse des inclusions fluides a permis de contraindre les conditions pré-éruptives des néphélinites de Saghro à 1.7–2.2 GPa et ~1350 °C. Les minéraux montrent que les magmas néphélinitiques sont riches en éléments volatils (Cl, F, S), et les inclusions fluides indiquent que les magmas étaient saturés en fluide riche en CO2 à des pressions > 590 MPa. Les différents assemblages minéralogiques des néphélinites et la présence de xénolites péridotitiques suggèrent une ascension rapide des néphélinites à olivine et des processus plus complexes en profondeur pour les néphélinites à pyroxène. La modélisation des processus de cristallisation fractionnée et de fusion partielle des laves mafiques de Saghro a permis de déterminer qu’elles sont issues de faibles taux de fusion partielle (0.6–2.5 %) d’une péridotite carbonatée enrichie en éléments incompatibles, au niveau de la transition grenat–spinelle (~80–85 km) et en présence d’amphibole. Les néphélinites de Saghro montrent une évolution temporelle avec une légère augmentation du taux de fusion et une diminution de la quantité d’amphibole au résidu des plus anciennes (néphélinites à olivine, 9.6 Ma) aux plus récentes (néphélinites à pyroxène, 2.9 Ma). Les basanites forment un système indépendant des néphélinites et sont issues de taux de fusion plus élevés. Les fortes variations dans leur composition chimique suggèrent qu’elles ont subi de la cristallisation fractionnée lors de leur ascension. Les caractéristiques particulières des néphélinites et basanites de Saghro (enrichissement en éléments incompatibles, anomalies négatives en K, Zr, Hf et Ti, rapports Ca/Al et Zr/Hf élevés) indiquent que leur source a subi un métasomatisme principalement carbonatitique. L’influence de ce métasomatisme est plus forte pour les néphélinites à pyroxène que pour les néphélinites à olivine, impliquant une évolution temporelle de l’intensité du métasomatisme. Ces résultats suggèrent des interactions fluide-roche sous le craton Nord-Ouest Africain, entraînant la formation d'un manteau métasomatisé par des composants carbonatitiques riches en CO2 au niveau de la transition lithosphère-asthénosphère. L’origine du métasomatisme provoquant l’enrichissement de la source et la formation de veines d’amphibole pourrait être liée à la fusion de reliquats de croûte océanique subductée. Les températures de fusion relativement faibles (< 1350 °C) suggèrent l’absence d’anomalie thermique sous le Jbel Saghro, et favorisent donc un modèle de délamination de la lithosphère comme initiateur du volcanisme. Cependant, l’augmentation du taux de fusion partielle au cours du temps, également observée dans le Moyen Atlas, et les similitudes isotopiques et géochimiques avec les laves alcalines des îles Canaries ne permettent pas d’exclure une influence du panache des Canaries sur la source du volcanisme alcalin du Jbel Saghro
Volatile-rich, silica-undersaturated alkaline lavas record the important role of fluids during fluid-rock and magma-rock interactions in the mantle, which are key processes to understand the dynamics of the convective mantle and lithosphere-asthenosphere interactions in intracontinental settings. The aim of this thesis is to bring new constraints on the genesis of alkaline magmas by characterizing the crystallization conditions, the source and the partial melting processes taking part in the genesis of olivine nephelinites, pyroxene nephelinites and basanites from the Jbel Saghro volcanic field in the Moroccan Anti Atlas. The petrological and geochemical study of rocks and minerals coupled with the analysis of fluid inclusions constrains the pre-eruptive conditions of Saghro nephelinites to 1.7–2.2 GPa and ~1350 °C. Minerals show that nephelinitic magmas are rich in volatile elements (Cl, F, S), and fluid inclusions indicate that magmas were saturated with a CO2-rich fluid at pressures > 590 MPa. The various mineralogical assemblages and the presence of peridotite xenoliths suggest a rapid ascent for olivine nephelinites and more complex processes at depth for pyroxene nephelinites. Fractional crystallization and partial melting modelling of Saghro mafic lavas indicate that they are low-degree melts (0.6–2.5 %) of an amphibole-bearing carbonated peridotite enriched in incompatible elements, at the garnet-spinel transition (~80–85 km). Saghro nephelinites display a temporal evolution with a slight increase of the degree of melting and a decrease of the amount of residual amphibole from the oldest (olivine nephelinites, 9.6 Ma) to the most recent (pyroxene nephelinites, 2.9 Ma). Basanites form a system that is independent from nephelinites and are slightly higher-degree melts. Important variations in their chemical composition suggest variable amounts of fractional crystallization during ascent. The peculiar characteristics of Saghro nephelinites and basanites (enrichment in incompatible elements, negative anomalies in K, Zr, Hf and Ti, high Ca/Al and Zr/Hf ratios) indicate that their source was affected by carbonatitic metasomatism. The influence of this metasomatism is stronger for pyroxene nephelinites than for olivine nephelinites. These results suggest fluid-rock interactions beneath the Northwest African Craton, leading to the formation of a metasomatized mantle by CO2-rich carbonatitic components at the lithosphere-asthenosphere transition. The origin of the metasomatism inducing source enrichment and the formation of amphibole veins could be attributed to the melting of relict subducted oce anic lithosphere. The relatively low melting temperatures (< 1350 °C) suggest the absence of a thermal anomaly beneath the Jbel Saghro, and thus support a lithosphere delamination model as precursor of Saghro volca0,3nism. However, the increasing degree of partial melting over time, also observed in the Middle Atlas, together with the isotopic and geochemical similarities with Canary Islands alkaline lavas does not allow us to discard the influence of a deviation of the Canary mantle plume beneath northwest Africa

Styles APA, Harvard, Vancouver, ISO, etc.

9

Berg, Sylvia. « Disintegration and Devolatilisation of Sandstone Xenolith in Magmatic Conduits : an Experimental Approach ». Thesis, Uppsala universitet, Berggrundsgeologi, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-160266.

Texte intégral

Résumé :

Xenoliths preserve evidence of magma-crust interactions in magmatic reservoirs and conduits. They reveal processes of partial melting of country rock, and disintegration into magma. Widespread evidence for frothy xenoliths in volcanic deposits exists, and these evidently indicate processes of gas liberation, bubble nucleation and bubble growth. This report focuses on textural analysis of frothy sandstone xenoliths from Krakatau in Indonesia, Cerro Negro in Nicaragua, Cerro Quemado in El Salvador and from Gran Canaria, Canary Islands, and involves attempts to experimentally reproduce xenolith textures. To achieve this, magmatic conditions acting upon country rock in volcanoes are simulated by subjecting sandstones to elevated temperature and pressure in closed system-autoclaves. Subsequent decompression imitates magma ascent following xenolith entrainment, and is largely responsible for the formation of frothy xenolith textures. The experiments show a range of successive features, such as partial melting, gas-pressure build up, bubble nucleation, growth and development of bubble networks. The experiments closely reproduced textures of natural xenoliths and help to assess the controlling P-T parameters that encourage efficient bubble growth. Conditions proved ideal between 850˚C and 870˚C and pressure release from 1 kbar. Such conditions limit bubble overprinting by secondary crystallization and melt infilling. Country rock lithology proved vital regarding gas pressure build-up and resulting bubble nucleation during decompression. In particular, increased water content and relict crystals in the melt produced appear to ease and promote gas liberation by enabling early and effective bubble nucleation. Moreover, experiments confirm a decisive role for bubble coalescence. These results attest to the great potential of country rock to develop interconnected bubble networks upon magma contact, exsolving large amounts of crustal volatiles into the magma. Volatile input involves a change in magma viscosity and thus an accompanied change in disruptive behaviour, and may hence be responsible for increased potential to cause explosive volcanic eruptions. Moreover, H2O and CO2 vapour are severe greenhouse gases, which seems to be added to the atmosphere from crustal rocks via recycling by volcanic activity, and may have yet underappreciated effects on Earth’s climate.

Styles APA, Harvard, Vancouver, ISO, etc.

10

Laumonier, Mickaël. « Mélange de magmas à HP-HT : contraintes expérimentales et application au magmatisme d'arc ». Phd thesis, Université d'Orléans, 2013. http://tel.archives-ouvertes.fr/tel-00859628.

Texte intégral

Résumé :

Trois magmas (haplotonalite synthétique, basalte et dacite de Santorin) ont été juxtaposés et déformés à l'aide d'une presse de type Paterson pour contraindre les conditions de mélange de magmas à haute pression (300 MPa). Ces trois magmas ont été utilisés en conditions sèches ou hydratées et dans une gamme de température comprise entre 600 et 1200°C, permettant d'obtenir plusieurs fractions cristallines et contrastes de viscosité. Les textures de mélange produites lors des expériences dépendent de la fraction cristalline et sont similaires aux textures rencontrées dans la nature. Les textures de mélange mécanique (mingling) produites sont la ségrégation de cristaux depuis leur magma source, la formation d'enclaves par détachement et de filaments par étirement de parcelles de magma. Le mélange chimique (mixing) est illustré par des zones d'interactions comportant une large variété de liquides intermédiaires et la cristallisation de nouvelles phases. Le mélange est produit en l'absence d'une charpente cristalline dans l'un ou l'autre des magmas, si le contraste de viscosité est faible (< 0,3 unité log) et en dessous d'un seuil de viscosité absolue, déterminé entre 107 et 108 Pa.s. Par ailleurs, l'eau joue un rôle important sur les propriétés rhéologiques des magmas, et donc sur leurs capacités de mélanges : elle abaisse le seuil de mélange de près de 200°C entre des magmas saturés en eau, et son exsolution (présence de bulles) entraîne une réduction significative des viscosités promouvant le mélange à des fractions cristallines plus faibles. Les conditions rhéologiques favorables aux mélanges entre le magma d'un réservoir et un magma plus chaud qui le recharge ont été déterminées selon la fraction de magma injecté. Cette fraction est de 0,5 minimum pour la majorité des réservoirs typiques du contexte d'arc. La comparaison avec des systèmes plutoniques et volcaniques exposant des figures de mélange montre que les conditions favorables aux mélanges sont atteintes avec des fractions inférieures. Ceci suggère que le fonctionnement d'un réservoir magmatique est influencé par ses styles et taux de recharge, ainsi que la quantité de volatils.

Styles APA, Harvard, Vancouver, ISO, etc.

11

Bourgue, Emmanuelle. « Effets des volatils CO2 et H2O sur les propriétés rhéologiques des magmas ». Paris, Institut de physique du globe, 2003. http://www.theses.fr/2003GLOB0006.

Texte intégral

Résumé :

Les processus volcanologiques sont gouvernés par de nombreux paramètres physiques et chimiques (pression, température, composition chimique. . . ) qui exercent une grande influence sur les propriétés physiques des liquides silicatés (i. E. Magmatiques). Cependant, l'effet des volatils (gaz dissous) reste très mal connu. Leur présence dans les magmas joue pourtant un rôle primordial sur la fragmentation, le dégazage et le transport de ceux-ci. Les effets du CO2 et de H2O sur les propriétés rhéologiques (densité, viscosité, dilatation thermique) sont étudiés sur un liquide silicaté synthétique simple pour CO2, et sur un liquide basaltique pour H2O, le basalte étant la roche magmatique la plus répandue sur la surface de la Terre. L'ensemble des résultats obtenus permet une meilleure compréhension de l'interaction eau-magma en fonction de la chimie et apporte des résultats nouveaux quant à l'effet du CO2 dissous. Volcanological processes are governed by many physical and chemical parameters such as pressure, temperature and chemical composition, bubble and crystal content. . . These parameters are known for exerting a stong influence on the physical properties of silicate melts (i. E. Magmas). However, the effects of dissolved volatiles is still poorly understood, although their presence play an essential role in fragmentation, degassing and magma transport. The effects of CO2 and H2O, the two most abundant volatiles in magmas, are investigated, on the rheological properties (density and volume, viscosity, and thermal expansion) of a simple synthetic silicate melt for CO2, ans a basaltic melt for H2O, basalt being the most widely spread composition on the surface of the planet. The results allow a much better comprehension of the water/magma interactions depending on chemical composition, and bring new data regarding the effect of dissolved CO2

Styles APA, Harvard, Vancouver, ISO, etc.

12

Blower, Jonathan David. « Degassing processes in volcanic eruptions ». Thesis, University of Bristol, 2001. http://hdl.handle.net/1983/30b2bc8c-2956-4a7a-a801-cdbef473ee1a.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

13

Crandall, Jake Rauch. « Magma-Sediment Interaction on Mars : Detectability and Habitability as Constrained by Terrestrial Analogs ». OpenSIUC, 2021. https://opensiuc.lib.siu.edu/dissertations/1944.

Texte intégral

Résumé :

Magmatism is a critical process throughout the geological history of Earth and Mars, and one of the few processes capable of producing significant changes in the Martian surface and subsurface past the Noachian. The interaction between mafic magmatism and host rock has the potential to contribute to the surface volatile species, chief among which is sulfur. On Earth, mafic magmas intruding sulfur-rich sediments are rare; however, sulfur–rich soils exist with a near global extent on Mars, and evidence exists for both recent and ancient mafic magmatism. The intrusion of mafic magmas into sulfur-rich sediments is therefore expected on Mars, and is especially pertinent concerning proposed landing site for the ESA ExoMars mission, and the landing site of the NASA Mars 2020 mission, both of which are in proximity to a potential volcanic capping unit in direct contact with sulfate bearing sediments. Here we investigate a terrestrial analog in the San Rafael Swell on the Colorado Plateau in which numerous mafic dikes intrude, alter, and bake sulfur-rich sediments. Mafic dikes intruding the Curtis, Entrada Sandstone, and Carmel Formations act as analogs for volcanic/sediment interaction on Mars, specifically for Jezero Crater, Mawrth Vallis, and N-E Syrtis Major. Using Mars relevant instruments, mineralogical changes with respect to distance from the magmatic intrusion, as well as the spatial resolution necessary to detect these changes, are constrained. The investigated analogs are discovered to be dynamic, and similar systems on Mars will likely require both orbital and in-situ measurements to be detected due to resolution constraints.

Styles APA, Harvard, Vancouver, ISO, etc.

14

Myers, Madison. « Storage, Ascent, and Release of Silicic Magma in Caldera-Forming Eruptions ». Thesis, University of Oregon, 2017. http://hdl.handle.net/1794/22692.

Texte intégral

Résumé :

The mechanisms and timescales associated with the triggering of caldera-forming eruptions remain ambiguous and poorly constrained. Do such eruptions start vigorously, then escalate, or can there be episodicity? Are they triggered through internal processes (e.g. recharge, buoyancy), or can external modulations play an important role? Key to answering these questions is the ability to reconstruct the state of the magma body immediately prior to eruption. My dissertation research seeks to answer these questions through detailed investigation of four voluminous caldera-forming eruptions: (1) 650 km3, 0.767 Ma Bishop Tuff, Long Valley, (2) 530 km3, 25.4 ka Oruanui eruption, Taupo, (3) 2,500 km3, 2.08 Ma Huckleberry Ridge Tuff, Yellowstone and (4) 250 km3, 26.91 Ma Cebolla Creek Tuff, Colorado. The main techniques I applied integrated glass geochemistry (major, trace and volatile), diffusion modeling, and detailed field sampling. In chapters two, three, and four these methods are applied to the initial fall deposits of three supereruptions (Bishop, Oruanui and Huckleberry Ridge) that preserve field-evidence for different opening behaviors. These behaviors range from continuous deposition of fall deposits and ignimbrite (Bishop), to repetitive start/stop behavior, with time breaks between eruptive episodes on the order of weeks to months (Oruanui, Huckleberry Ridge). To reconstruct the timescales of opening activity and relate this to conduit processes, I used two methods that exploit diffusion of volatiles through minerals and melt, providing estimates for the rate at which magmas ascended to the surface. This knowledge is then integrated with the pre-eruptive configuration of the magma body, based on melt inclusion chemistry, to interpret what triggered these systems into unrest. Finally, in chapter five I take a different approach by integrating geochemical data for melt inclusions and phenocryst minerals to test whether the mechanism of heat and volatile recharge often called upon to trigger crystal-rich dacitic magmas (the so-called monotonous intermediates), is applicable to the Cebolla Creek Tuff. This dissertation includes both previously published and unpublished co-authored material, and three online supplementary excel files.

Styles APA, Harvard, Vancouver, ISO, etc.

15

Iacovino, Kayla. « An unexpected journey : experimental insights into magma and volatile transport beneath Erebus volcano, Antarctica ». Thesis, University of Cambridge, 2014. https://www.repository.cam.ac.uk/handle/1810/245333.

Texte intégral

Résumé :

Erebus is a well-studied open-vent volcano located on Ross Island, Antarctica (77◦ 32’ S, 167◦ 10’ E). The volcano is the focus of ongoing research aimed at combining petrologic data and experiments with surface gas observations in order to interpret degassing histories and the role of volatiles in magma differentiation, redox evolution, and eruptive style. This research focus has been driven in part by an abundance of studies on various aspects of the Erebus system, such as physical volcanology, gas chemistry, petrology, melt inclusion research, seismic, and more. Despite this large data set, however, interpretations of Erebus rocks, particularly mafic and intermediate lavas, which are thought to originate from deep within the magmatic plumbing system, have been hindered due to a lack of experimental data. Experimental petrology is a common tool used to understand volcanic plumb- ing systems and to tie observations made at the Earth’s surface to the deep pro- cesses responsible for driving volcanic activity. Experimental petrologists essen- tially recreate natural magma chambers in miniature by subjecting lavas to con- ditions of pressure, temperature, and volatile chemistry (P-T-X) relevant to a natural underground volcanic system. Because many important parameters can be constrained in the laboratory, the comparison of experimental products with naturally erupted ones allows for an understanding of the formation conditions of the rocks and gases we see at the surface. In this thesis, I have employed experimental and analytical petrological tech- niques to investigate the magmatic plumbing system of Erebus volcano. Broadly, the research is focused on volatiles (namely H2O, CO2, and S species) in the Ere- bus system: their abundances, solubilities, interactions, evolution, and ultimate contributions to degassing. Specifically, three key themes have been investigated, each employing their own experimental and analytical techniques. Firstly, the mixed volatile H2O-CO2 solubility in Erebus phonotephrite has been investigated under P-T-X conditions representative of the deep plumbing system of Erebus. Understanding the deep system is crucial because the constant supply of deeply derived CO2-rich gases combined with a sustained energy and mass input into the lava lake suggests a direct link between the phonolite lava lake and the volcano’s ultimate mantle source via a deep mafic plumbing system. Secondly, I have mapped the phase equilibria and evolution of primitive, inter- mediate, and evolved Erebus lavas. The chemistries of these experimental products span the full range of lavas on Ross Island and help to constrain magmatic evolu- tion from basanite to phonolite as well as to elucidate the geometry of the deep Ross Island plumbing system. Finally, lower-pressure experiments representing the shallow plumbing system at Erebus have been performed in order to understand the transport properties of sulfur in alkaline magma. Experiments were performed on natural Erebus basanite and phonolite, which represent the most primitive and evolved lavas from Erebus. A distinct cocktail of C-O-H-S fluid was equilibrated with each experiment, and a wide range of experimental oxygen fugacities was explored. Overall, experiments from this work are the first to place constraints on the en- tire magma plumbing system of Erebus volcano. In addition, experimental results foster a new understanding of non-ideal gas behavior at high pressure, the affinity of CO2 to deeply sourced rift magmas, and the effect of alkalis on fluid transport capabilities in melts.

Styles APA, Harvard, Vancouver, ISO, etc.

16

Moune, Séverine. « Volatils mineurs (S, Cl, F) et éléments traces dans les magmas pré-éruptifs et les gaz volcaniques ». Clermont-Ferrand 2, 2005. https://tel.archives-ouvertes.fr/tel-00011542/document.

Texte intégral

Résumé :

Une étude sur les inclusions magmatiques (MIs) a permis de suivre l'évolution des volatils dissous dans les systèmes magmatiques des volcans Hekla et Masaya au cours de la différenciation magmatique (cristallisation fractionnée). Les concentrations en volatils dissous ''attendues'' dans les liquides pré-éruptifs ont donc pu être estimées, permettant ainsi de ne pas sous-estimer les concentrations des liquides piégés dans les MIs et d'améliorer les contraintes sur la masse de volatils émise dans l'atmosphère. La chimie des phases gazeuses de ces volcans a également été étudiée. Ceci a montré que l'enrichissement des éléménts traces volatils est lié à un processus de dégazage sous forme d'halogénures et sulfates à Hekla et sous forme de chlorures, sulfates et chloro-sulfates au Masaya. En revanche, l'enrichissement des éléments réfractaires à Hkla est expliqué par un processus de dissolution non-stoechiométrique des téphras par la phase gazeuse riche en fluor au sein du panache éruptif

Styles APA, Harvard, Vancouver, ISO, etc.

17

Hartsock, Tanner. « Magma evolution, P-T conditions and volatile degassing of a steady-state volcano : Yasur, Vanuatu ». Thesis, University of Iowa, 2019. https://ir.uiowa.edu/etd/6757.

Texte intégral

Résumé :

Yasur is an active scoria cone volcano in the Siwi Caldera on the island of Tanna, Vanuatu, in the South Pacific. This volcano has been erupting continuously for the last 800 years and is the latest manifestation of episodic volcanic activity in this area dating back to the late Pliocene. Yasur eruptions consist of intermittent Strombolian-style explosions of pyroclastic debris with emissions of volatiles such as SO₂, HCl and HF. Other than CO2 and H2O, the most abundant gas emitted from Yasur is sulfur, and plume monitoring has confirmed the volcano as one of the largest point sources of sulfur on the planet with an average flux of 600-1400 tons/day. Fluorine poses a chronic environmental health risk on Tanna, so understanding long-term exposure rates as well as periodic increases in volcanic intensity will help to better quantify its risk. In this study we gauge compositional variation of magma using fresh pyroclastic bombs collected over a 3-month period from August to November, 2016. Our results suggest long-term broad compositional stability in both the whole-rock and groundmass glass and minerals. Our results show slight variation in volatile phases in both olivine-hosted melt inclusions and groundmass glass over an intensively sampled 3-month period, which suggests that the plumbing beneath Yasur harbors an open-system degassing environment. Volcanic eruptions are usually driven by magma mixing, however, our results show no compositional variation in phenocrysts. We show that Yasur is an excellent example of an inefficiently degassed volcano, and that volcanic activity is controlled by volatile flux. We also use cotectic compositional data to calculate pressure and temperature conditions within the magma chamber and assess fluxes of volatiles from the magma using melt inclusion analyses for S and Cl. Our study places new bounds on the vertical extent of the magma chamber and suggests differentiation from a basaltic trachyandesite at depths of up to 12 km.

Styles APA, Harvard, Vancouver, ISO, etc.

18

Khadhem, Laith. « Volatilernas påverkan på marina vulkanutbrott ». Thesis, Uppsala universitet, Institutionen för geovetenskaper, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-328231.

Texte intégral

Résumé :

The Cape Verde archipelago is located 2000 km east of the Atlantic oceanic ridge and 500 km west of the western part of Africa. The plateau of the archipelago rises on average 2 km above the seafloor, which makes it one of the highest oceanic plateaus on Earth. Cape Verde originates from hotspot formation, a geological phenomenon which takes place beyond the tectonic plate boundaries where magma rises to the surface. In this thesis, volcanic material taken from the Charles Darwin volcanic field at a depth of more than 3000 meter and made up by four basaltic rocks and one agglomerate will be investigated. The agglomerate and vesicles in the rock shows that explosive volcanism occurs in high water depths, which is generally not common. Therefore, the material will be investigated to find out how explosive volcanism can occur at high water depths. The investigation will be based on quantifying the number of vesicles to able to calculate their area and analyze the magmatic water content in clinopyroxene crystals taken from the agglomerate by FTIR spectroscopy. Water is a volatile substance in the composition of magma and has a huge effect on its behavior at eruption. The results of quantification show that the area taken by vesicles varies from 7- 54 % which shows that magmatic products with high number of vesicles are common. The FTIR analysis shows that the magmatic water content can be high enough to cause an oversaturated magma system, which creates explosive eruptions. This statement is based on only one clinopyroxene crystal that had a magmatic water content of 3,87 ± 0,77 %. Other possible reasons for explosive eruptions at high water depth are the CO2 content in the magma and the size of volcanic vent.
Kap Verde är en arkipelag, situerad cirka 2000 km öster om den mittatlantiska spridningsryggen och 500 km väster om det afrikanska fastlandet. Arkipelagens platå har en genomsnittlig höjd på 2 km, vilket gör den till en av världens högsta oceaniska platåer. Arkipelagen har uppkommit av hetfläcksbildning, ett geologiskt fenomen baserad på att magma erupteras till ytan där jordskorpan är förtunnad och inte har någon anknytning till de tektoniska plattgränserna. Det som undersöks i detta kandidatarbete är vulkaniskt material, taget från den vulkaniska undervattensön Charles Darwin vulkanfält som ligger i den västra del Kap Verdes norra ö-grupp på över 3000 meterdjup. Materialet består av ett agglomerat och fyra stenstuffer av basaltisk komposition. Agglomeratet tyder på att explosiva vulkanutbrott förekommer, vilket även bekräftas av stenstufferna som har rikligt förekomst av luftbubblor. Explosiva vulkanutbrott är generellt inte förekomliga vid höga vattendjup, därav undersöks materialet för att kunna reda ut orsakerna som ger upphov till förekomsten av explosiva vulkanutbrott. Undersökningen baseras på att kvantifiera luftbubblor hos stenstufferna för att kunna räkna ut arean som upptas och analysera vattenhalten i klinopyroxenkristaller i agglomeratet med hjälp av FTIR spektroskopi. Vatten tillhör de flyktiga beståndsdelar i magmas sammansättning som kallas för volatiler och utgör en viktig parameter för magmans uppträdande vid eruption. Resultatet kvantifiering av luftbubblor visar att arean som upptas av luftbubblor varierar mellan 7–54 % av stenstufferna total area, vilket understryker att magmatiska produkter med hög andel luftbubblor är förkomliga. FTIR analysen visar att det finns tillräckliga höga vattenhalter för ett övermättat magmasystem som ger upphov till vulkanutbrott med explosiva förlopp, baserat på vattenhalten 3,87 ± 0,77 % av en klinopyroxenkristall. Andra möjliga orsaker till uppkomsten av magmatiska produkter med hög andel luftbubblor är koldioxidhalten i magman och storleken på vulkanrören.

Styles APA, Harvard, Vancouver, ISO, etc.

19

Esposito, Rosario. « Studies of volatile evolution in magmatic systems using melt inclusions ». Diss., Virginia Tech, 2012. http://hdl.handle.net/10919/28287.

Texte intégral

Résumé :

Understanding volatile evolution associated with active volcanic magmatic systems is of paramount importance because volatiles control and determine the magnitude of an eruption owing to the large change in molar volume that volatile species show depending on their physical state (volatiles dissolved in silicate melts vs. volatiles exsolved as vapor). For active volcanic systems studying the volatile evolution can help to assess the potential hazard associated to a certain locality. Also, volatile evolution in magmatic system controls the formation of certain ore deposits. Despite the importance of understanding volatile evolution of magmatic systems, concentrations of volatiles of evolving magmas are not easily available especially for magmas originated in the deep crust. Fortunately, sample of melts can be entrapped as melt inclusion (MI) into growing igneous minerals in crystalizing magma chamber. After the entrapment, the crystal works as an insulating capsule from the external magmatic environment. Researchers have started to use MI because they provide some advantages in respect to the classical whole rock approach to petrological studies. One of the most important advantages is that MI often represent sample of a deep and non-degassed melt (glass) available at Earth's surface. In fact, with the exception of deep ocean basalts, igneous whole rocks found at the Earth's surface are degassed magmas. This dissertation is a compilation of four publications produced during six years of research and is addressed to give a contribution in understanding the volatile evolution in magmatic systems and also to improve the present understanding of information that can be obtained using the melt inclusions technique. In the first chapter, I present an alternative interpretation of H₂O-CO₂ trends obtained from MI. In this study, we demonstrate that these trends can be due to post entrapment crystallization on the wall of the MI and not to magma ascent. This alternative view is more realistic especially for cases where in the same phenocrysts MI show strongly different CO₂ concentrations. In the second chapter, I present a study to test for the MI reliability in recording volatile concentrations. We used the approach of the melt inclusion assemblage (MIA) that consists of analyzing groups of MI presumably entrapped at the same time and, thus, at same chemical and physical conditions. The results show that most of the MIA studied show consistent volatile concentrations corroborating the reliability of the MI technique. CO₂ shows the highest degrees of variability and we have assessed this behavior mostly to C-contamination in the surface of the sample. The third chapter is a study case (the Solchiaro eruption in Southern Italy) that shows the potential uses of MI to understanding the volatile evolution. I present a model showing the dynamic of the magma based on MI. This study also discusses the origin of anomalous MI and which MI provide the best information. The final chapter is dedicated to test the applicability of the new Linkam TS1400XY heating stage. I was able to show how this new microthermometric tool is capable of homogenizing MI at high temperature and to quench MI to a homogeneous glass state.
Ph. D.

Styles APA, Harvard, Vancouver, ISO, etc.

20

Walowski, Kristina. « From Cinder Cones to Subduction Zones : Volatile Recycling and Magma Formation beneath the Southern Cascade Arc ». Thesis, University of Oregon, 2015. http://hdl.handle.net/1794/19310.

Texte intégral

Résumé :

Volatiles (H2O, CO2, S, Cl) play a key role in magmatic processes at subduction zones. In this study, the dissolved volatile contents of olivine-hosted melt inclusions from cinder cones in the Lassen segment of the Cascade arc are used to investigate dehydration of subducted oceanic lithosphere, magma formation in the sub-arc mantle wedge, and mafic magma storage and evolution in the crust. Relatively young, hot oceanic lithosphere subducts beneath the Cascade arc. The hydrogen-isotope and trace-element compositions of melt inclusions, when integrated with thermo-petrologic modeling, demonstrate that fluids in Cascade magmas are sourced from hydrated peridotite in the deep slab interior and that the oceanic crustal part of the slab extensively dehydrates beneath the forearc. In contrast to their slab-derived H, the melt inclusions have B concentrations and isotope ratios that are similar to mid-ocean ridge basalt (MORB), requiring little to no slab contribution of B, which is also consistent with extensive dehydration of the downgoing plate before it reaches sub-arc depths. Correlations of volatile and trace element ratios in the melt inclusions (H2O/Ce, Cl/Nb, Sr/Nd) demonstrate that geochemical variability in the magmas is the result of variable amounts of addition of a hydrous subduction component to the mantle wedge. Radiogenic isotope ratios require that the subduction component has less radiogenic Sr and Pb and more radiogenic Nd than the Lassen sub-arc mantle and is therefore likely to be a partial melt of subducted Gorda MORB. These results provide evidence that chlorite-derived fluids from the deep slab interior flux-melt the oceanic crust, producing hydrous slab melts that migrate into the overlying mantle, where they react with peridotite to induce further melting. The basaltic magmas that erupted at Cinder Cone near Mt. Lassen trapped melt inclusions during olivine crystallization at ~7-15 km depth. The melt inclusion compositions require that two different mantle-derived magmas were involved in the eruption, and temporal changes show that arrival of the two batches correlates with two explosive phases of activity. Both magmas experienced rapid crustal contamination before erupting, illustrating the complexities of cinder cone eruptions. This dissertation includes previously published and unpublished co-authored material.

Styles APA, Harvard, Vancouver, ISO, etc.

21

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.

Texte intégral

Résumé :

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.

Styles APA, Harvard, Vancouver, ISO, etc.

22

Kunrat, Syegi Lenarahmi. « Soputan Volcano, Indonesia : Petrological Systematics of Volatiles and Magmas and their Bearing on Explosive Eruptions of a Basalt Volcano ». PDXScholar, 2017. https://pdxscholar.library.pdx.edu/open_access_etds/3828.

Texte intégral

Résumé :

Soputan volcano is one of the few basaltic volcanoes among 127 active volcanoes in Indonesia. It is part of the Sempu-Soputan volcanic complex located south of Tondano Caldera, North Sulawesi and commonly produces both explosive eruptions with VEI 2-3 and effusive lava dome and flow eruptions. Over the last two decades, Soputan had thirteen eruptions, the most recent in 2016. Most eruptions started explosively, followed by dome growth and in some cases pyroclastic flows. Our study focuses on understanding the magmatic system of Soputan and what processes are responsible for its highly explosive eruptions, which are typically uncommon for a basaltic magma composition. Our study includes tephra samples predating the 1911 eruptions, lava flow samples from the 2015 eruption, and ash from a 2015 fallout deposit. Our whole rock major and trace element composition are virtually identical to lava flow and select pyroclastic deposit compositions of Kushendratno et al. (2012) for the 1911-1912 and 1991-2007 eruptions. Bulk rocks contain 49 to 51 wt.% SiO2, whereas 2015 ash samples are slightly more silicic with 53 wt.% SiO2, consistent with segregation of groundmass from phenocrysts in the eruption cloud. Mantle normalized incompatible trace elements indicate strongly depleted HFSE (High Field Strength Elements) and REE (Rare Earth Elements) signatures but with spikes at Pb and Sr and mild enrichment of Rb and Ba. In comparison of data of this study with what was reported by Kushendratno et al. (2012), Fo68-79 olivine-hosted melt inclusions range from basaltic (48-52 wt.% SiO2) to basaltic andesite (54-55 wt.%) as compared to 54 - 65 wt.% SiO2 glass in Fo68-74 olivines. The compositional range of melt inclusions is consistent with 50% fractionation of multiple minerals including observed phenocrysts of olivine, plagioclase, pyroxene and oxides. Compositional trends with an inflection point likely reflect a change in the crystallizing assemblage, where early crystallization includes clinopyroxene and plagioclase, while later crystallization is dominated by plagioclase. New volatile concentration data from melt inclusions (S max. 0.35 wt.%, Cl max. 0.17%, H2O max. 5.2 wt.% from FTIR analyses) are higher than previously reported from younger samples (S max. ~0.07 wt.%, Cl max. 0.2%, H2O max. ~1 wt.%). H2O is relatively constant (~1-4 wt.%) for individual tephra samples (data by FTIR and water by difference method). Our inclusion data suggest that more volatile-rich magmas exist at depth and this is consistent with a model whereby recharge of deep, volatile-rich magmas into a more degassed and crystal-rich magma initiates a new, highly explosive eruption.

Styles APA, Harvard, Vancouver, ISO, etc.

23

Bureau, Hélène. « Les éléments volatiles associés aux magmas du Piton de la Fournaise : une approche par l'étude des inclusions fluides et vitreuses ». Paris 7, 1996. http://www.theses.fr/1996PA077023.

Texte intégral

Résumé :

Le piton de la fournaise (ile de la reunion, ocean indien) est un volcan bouclier basaltique actif dont l'existence est due a un point chaud. Il a comme caracteristiques d'emettre regulierement de grandes quantites d'oceanites et de ne presenter aucun degazage permanent en surface. L'etude des inclusions vitreuses et fluides piegees lors de la cristallisation des mineraux en profondeur permet de caracteriser la composition des magmas a differentes etapes de leur evolution. Elles constituent l'unique moyen de caracteriser la phase volatile associee aux magmas du piton de la fournaise et de suivre son evolution. Les compositions des inclusions vitreuses primaires piegees dans des olivines pyroclastiques (mg82-87) d'oceanites du piton de la fournaise confirment le caractere transitionnel des basaltes de l'ile de la reunion et mettent en evidence differentes sources mantelliques pour les differents echantillons sur la base des teneurs en elements majeurs (correlation inverse na#2o+k#2o versus sio#2). On distingue deux groupes d'echantillons, correspondant a deux types d'alimentation distincts: les echantillons les plus primitifs, qui sont pieges le plus profondement de ptotale 1,8 a 4 kbars, dans des olivines mg85-87 et dont les compositions sont mgo 9,3-9,7%pds, k#2o 0,54-0,58%pds, ces echantillons correspondent a un melange de magmas parentaux ; les echantillons plus evolues pieges pres de la surface de ptotale 1,3 a 0,1 kbars, dans des olivines mg85-82, de compositions mgo 8-9%pds, k#2o 0,62-0,73%pds, correspondant a differents magmas parentaux. Les teneurs en carbone sont plus importantes dans les echantillons primitifs (220-550 ppmc) que dans les echantillons evolues (0-140 ppmc). Le caractere transitionnel de ces basaltes, marque par les elements majeurs, est confirme par les teneurs en elements volatils. Par exemple, on observe que les teneurs en eau (0,56-1,26%pds) sont intermediaires entre basaltes tholeiitiques et basaltes alcalins. Les teneurs en chlore seraient plutot caracteristiques de basaltes alcalins avec 200 a 300 ppm, alors que les teneurs en soufre sont comparables aux basaltes oceaniques (morbs) de 400 a 1550 ppm. Les teneurs en fluor varient de 440 a 560 ppm. De plus, les differents magmas parentaux se distinguent sur la base de leurs rapports d'elements volatils et incompatibles: k#2o/h#2o, c/h#2o, h#2o/f, p#2o#5/f, k#2o/f, cl/f, on estime que les teneurs en eau et carbone des sources mantelliques sont respectivement comprises entre 0,8 et 1,5%pds et entre 1460 et 4100 ppmc. Les teneurs en eau, carbone, chlore, soufre sont donc comprises entre celle des basaltes tholeiitiques (morbs) et celles des basaltes alcalins. Elles suggerent que la profondeur de la zone mantellique source des basaltes transitionnels est intermediaire entre celle moins profonde des basaltes tholeiitiques (morbs), et la zone mantellique source plus profonde des basaltes alcalins. L'etude couplee des inclusions vitreuses et fluides (riches en co#2) montre que le carbone degaze de facon continue depuis 5 kb (ptotalepco#2) jusqu'a la surface. Ces resultats mettent en evidence la saturation du magma en carbone. La presence de globules de sulfures atteste d'une saturation en soufre des magmas. Les degazages de l'eau et du soufre sont observes en fin de parcours du magma lors de son arrivee en surface

Styles APA, Harvard, Vancouver, ISO, etc.

24

Gomez-Ulla, Rubira Alejandra. « Historical eruptions of Lanzarote, Canary Islands : Inference of magma source and melt generation from olivine and its melt inclusions ». Thesis, Université Clermont Auvergne‎ (2017-2020), 2018. http://www.theses.fr/2018CLFAC023.

Texte intégral

Résumé :

L’étude des basaltes des îles océaniques (OIB) révèle la complexité du manteau terrestre, dont la composition chimique est hautement variable. Décrypter l’implication des lithologies des roches sources et des processus à l’origine des OIB est complexe car les magmas sont transformés lors de leur ascension jusqu’à la surface. Ceci est particulièrement critique dans le cas des îles Canaries, où la lithosphère est considérée comme particulièrement épaisse (>110 km Fullea et al., 2015). Aﬁn de mieux contraindre la composition chimique des magmas primitifs et les lithologies mantelliques plausiblement impliquées, deux éruptions historiques de l’île de Lanzarote, les éruptions de Timanfaya (1730-1736) et celles de 1824, ont été étudiées. En effet, ces deux éruptions offrent une opportunité unique d’étudier les mécanismes de génération des magmas et leurs compositions dans un contexte où le manteau est hétérogène. L’éruption de historique de Timanfaya (1730-1736) a émis des magmas qui ont évolué de basanites à basaltes alcalins, pour atteindre des compositions tholeitiques à la ﬁn de l’éruption. La dernière éruption de l’île, en 1824, a produit des basanites extrêmement riches en volatils. L’hétérogénéité du manteau est démontrée à l’extrême à Lanzarote où une seule éruption présente une variation de compositions chimiques équivalente à la diversité de celles des OIB dans le monde. L’extrême hétérogénéité est systématique pour les compositions des roches totales et des téphras à l’échelle d’une éruption, mais est encore ampliﬁée à l’échelle du minéral et des inclusions magmatiques contenus dans un même échantillon de téphra.Les concentrations des éléments traces et leurs rapports dans l’olivine (e.g. Ni, Mn et Ca) sont de précieux marqueurs des lithologies mantelliques à l’origine des magmas. En effet, les rapports Ni x (FeO/MgO), corrigé du fractionnement, et Fe/Mn sont des indicateurs de lithologies avec ou sans olivines. Il est considéré qu’ils peuvent montrer, dans la plupart des cas, l’ajout d’un liquide magmatique dérivé d’une pyroxénite dans les magmas primaires. La mesure des compositions des éléments traces des olivines des éruptions de 1730-1736 et de 1824 montrent les implications variables de plusieurs lithologies mantelliques au cours du temps. Lors de la fusion d’une lithologie ne contenant pas d’olivines, comme la pyroxénite, de hautes teneurs en Ni et de faibles teneurs en Mn et Ca sont attendues. Les basanites de Lanzarote présentent les plus grandes variations géochimiques, couvrant le champ compositionnel des olivines des MORB et des OIB du monde entier, tandis que les produits plus tardifs, c’est-à-dire les basaltes alcalins et les tholéites, ont des teneurs typiques de liquides magmatiques dérivés de pyroxénites. Les teneurs en forstérite (Fo) des olivines diminuent systématiquement avec le temps durant l’éruption de 1730-1736 et la proportion de liquide primaire saturé en silice augmente dans les mélanges de magmas primitifs avec le temps. A la ﬁn de l’éruption, les magmas tholéitiques cristallisent des olivines dont la teneur en Fo est faible, alors que les concentrations en Mn et Ca augmentent simultanément avec le rapport Ca/Al pour des rapports Fe/Mn et Ni x (FeO/MgO) relativement constants. Ces observations sont expliquées par une augmentation de la fusion par décompression à température légèrement plus faible. D’autre part, les basanites de l’éruption de 1824 possèdent les olivines ayant les teneurs en Fo les plus élevées, et des teneurs en éléments traces dépassant la variabilité des basanites de l’éruption de Timanfaya. Le fait que les basanites de Lanzarote contiennent des olivines dont les compositions en éléments traces recouvrant le champ des MORB et des liquides pyroxènitiques est expliqué par la fusion d’une source contenant des lithologies hétérogènes, induite par un ﬂux de CO2, générant ainsi des magmas aux compositions diverses. (...)
The study of oceanic island basalts (OIB) reveals the complexity of the mantle, which composition is highly variable. Deciphering the source lithologies and processes involved in the OIB formation is challenging since the magmas are transformed on their way to the surface. This is especially critical at Canary Islands where the lithosphere is thought to be remarkably thick (>110 km Fullea et al., 2015). In order to better constrain the composition of primitive magmas and the plausible mantle lithologies involved, two historical eruptions recorded at Lanzarote island, Timanfaya 1730-1736 and 1824 eruptions have been investigated. Indeed, these two eruptions offer a unique opportunity to investigate the mechanisms of magma generation and composition in the context of mantle heterogeneity. The Timanfaya, 1730-1736 historical eruption emitted magmas that evolved from basanites through alkali basalts, ﬁnally reaching tholeiitic compositions at the end of the eruption. In 1824 the last eruption on the island produced extremely volatile-rich basanite. The heterogeneity of the mantle is demonstrated to the extreme in Lanzarote where a single eruption exhibits compositional variations similar to the span of the OIB worldwide. The extreme heterogeneity is systematic from whole rock lava and tephra at eruption scale but ampliﬁed at mineral and melt inclusion scale within a single tephra sample of the eruption.The use of trace element concentrations and ratios of olivine (e.g. Ni, Mn, and Ca) are valuable indicators of the mantle source lithology, namely, the fractionation-corrected Ni x (FeO/MgO) and Fe/Mn as probes of olivine absent or present lithologies, often taken as pyroxenite-derived component in mixtures of primary melts. The measured trace element concentrations in olivine from the 1730-1736 and 1824 eruptions reveal variable mantle lithologies involved in the magma generation with time. Higher Ni and lower Mn and Ca contents are expected when melting Ol-free source, such as pyroxenite lithologies. The basanites exhibit the largest variation covering the range of olivine in MORB and OIB worldwide whereas later produced alkali-basalts and tholeites have values typically expected from pyroxenite derived melts. The Fo content decreases systematically with time during the 1730-36 eruption and the proportion of silica-saturated primary melt increased in the parental magma mixture with time. At the end of the eruption, tholeiite magmas crystallized olivine with lower Fo content, whereas those concentrations of Mn and Ca increased together with Ca/Al at relatively uniform Ni x (FeO/MgO) and Fe/Mn, all of which is readily explained by increased decompression melting at slightly lower temperature. The basanite from the eruption that took place in 1824 has olivine with the highest Fo content and trace element variability expanding the range of the Timanfaya basanite. The fact that Lanzarote basanites contain olivine with trace element systematic spanning that of MORB and pyroxenite melt is explained by CO2-ﬂux melting of a lithologically heterogeneous source, generating the diverse compositions. In addition, early reactive porous ﬂow through the depleted oceanic lithosphere and equilibration with harzburgite restite caused Ni depletion of the earliest percolating pyroxenite melt from which olivine crystallized and probably leaving dunite channels. After the channel formation mantle nodules could be brought to the surface. The fact that olivine compositions and basanite magma were reproduced approximately a century later may reﬂect episodic carbonatic ﬂuxing in the slowly uprising Canarian mantle plume. (...)

Styles APA, Harvard, Vancouver, ISO, etc.

25

Jolis, Ester M. « Magma-Crust Interaction at Subduction Zone Volcanoes ». Doctoral thesis, Uppsala universitet, Berggrundsgeologi, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-198085.

Texte intégral

Résumé :

The focus of this work is magma-crust interaction processes and associated crustal volatile release in subduction zone volcanoes, drawing on rock, mineral, and gas geochemistry as well as experimental petrology. Understanding the multitude of differentiation processes that modify an original magma during ascent to the surface is vital to unravel the contributions of the various sources that contribute to the final magmas erupted at volcanoes. In particular, magma-crust interaction (MCI) processes have been investigated at a variety of scales, from a local scale in the Vesuvius, Merapi, and Kelut studies, to a regional scale, in the Java to Bali segment of the Sunda Arc. The role of crustal influences is still not well constrained in subduction systems, particulary in terms of the compositional impact of direct magma crust interplay. To address this shortcoming, we studied marble and calc-silicate (skarn) xenoliths, and used high resolution short timescale experimental petrology at Vesuvius volcano. The marbles and calc-silicates help to identify different mechanisms of magma-carbonate and magma-xenolith interaction, and the subsequent effects of volatile release on potential eruptive behaviour, while sequential short-duration experiments simulate the actual processes of carbonate assimilation employing natural materials and controlled magmatic conditions. The experiments highlight the efficiency of carbonate assimilation and associated carbonate-derived CO2 liberated over short timescales. The findings at Merapi and Kelut demonstrate a complex magmatic plumbing system underneath these volcanoes with magma residing at different depths, spanning from the mantle-crust boundary to the upper crust. The erupted products and volcanic gas emissions enable us to shed light on MCI-processes and associated volatile release in these systems. The knowledge gained from studying individual volcanoes (e.g., Merapi and Kelut) is then tested on a regional scale and applied to the entire Java and Bali arc segment. An attempt is presented to distinguish the extent of source versus crustal influences and establish a quantitative model of late stage crustal influence in this arc segment. This thesis therefore hopes to contribute to our knowledge of magma genesis and magma-crust interaction (MCI) processes that likely operate in subduction zone systems worldwide.

Styles APA, Harvard, Vancouver, ISO, etc.

26

Salem, Lois Claire. « Magmatic processes at basaltic volcanoes : insights from the crystal cargo ». Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/277726.

Texte intégral

Résumé :

A plethora of magmatic processing occurs in magma reservoirs, where melts are stored prior to eruption. Magma reservoirs are complex, open systems, and often multiple reservoirs are partially inter-connected from source to surface, giving rise to the term 'volcanic plumbing system'. Parental melts feeding these reservoirs can have diverse and distinct geochemical and petrological characteristics, and be variably evolved or enriched. These melts can also bring with them a crystal cargo that may remain in equilibrium in the magma reservoir, but may also be modified by reaction, resorption, crystallisation and diffusion. Melts and crystals can be transported between reservoirs, from the upper mantle and through the crust, leading to melt mixing, reactions and volatile exsolution. Basaltic volcanic systems are fed by primitive melts, and due to the rapid ascent of melts and short magma storage times, these volcanoes provide the best means of unravelling the mantle and crustal contribution to geochemical heterogeneity observed in erupted samples. Despite the potential chemical complexity of a magma reservoir, evidence for magma processing and reaction can be preserved in melt inclusion suites and the compositional structure of their host crystals. Magmatic processes during storage and transport at two basaltic volcanoes are investigated using two carefully selected eruptions: the 1669 eruption at Mt. Etna, and the 2007 Father's Day eruption at Kīlauea. A suite of diverse geochemical, petrological and petrographical observations, made at a range of length-scales, are combined and interpreted in tandem with geophysical monitoring data. The conclusions of these studies shed light on the architecture of each volcano's plumbing systems and basaltic plumbing systems in general. This thesis is divided into two parts. The first study unravels the crustal and mantle processes controlling melt geochemical heterogeneity at Mt. Etna, Sicily, during the 1669 eruption, the largest eruption in historical times. The 1669 melt inclusion suite arises from the mixing of two basaltic melts with similar major element compositions but very different trace and volatile element compositions. The melt geochemistry suggests that at least one end-member melt has been heavily influenced by assimilation of carbonate in the crust. The elevation in alkalis, caused by carbonate assimilation, enhances carbon and sulfur solubility in one end member. The melt inclusion suite indicates that mixing of these melts occurred in the shallow crust shortly before eruption and this mixing may be the cause of the enhanced $CO_{2}$ fluxes prior to eruptions at Mt. Etna. The second study is split into two parts. Each uses the eruptive products of the Father's Day eruption at Kīlauea and aims to unravel the connectivity of the plumbing system between the summit and East Rift Zone, with a focus on timescales of storage and transport. The first part investigates the melt geochemistry in terms of heterogeneity and volatile composition, and the second investigates the crystal cargo in terms of features of the macro-scale crystal cargo distribution and the micro-scale geochemical zoning of individual crystals. The integration of observations and models from these two studies constrains the pressure, temperature and composition of source magma feeding the Father's Day eruption. The eruption is investigated in the context of the "magma surge'' event that preceded the intrusion, as well as within the context of the longer-term trends in Kīlauea geochemistry at the summit and East Rift Zone. Melt inclusion and matrix glass volatile systematics provide insights into the degassing path of the magma and the duration of magma transport to the surface is constrained by diffusion modelling. Estimated timescales for ascent by diffusion modelling of macrocryst major element composition, melt inclusion water content and the melt Fe$^{3+}$/Fe$_{tot}$ ratio are in agreement with timescales observed from the geophysical data of $< $8 hours from reservoir depth to eruption. Both studies emphasise how petrological observations can supplement geophysical monitoring datasets collected at the surface to aid our interpretation of volcanic behaviour and eruption forecasting.

Styles APA, Harvard, Vancouver, ISO, etc.

27

Gondé, Charlotte. « Etude expérimentale in situ du dégazage d'un magma rhyolitique ». Phd thesis, Université d'Orléans, 2008. http://tel.archives-ouvertes.fr/tel-00320491.

Texte intégral

Résumé :

La dynamique des éruptions volcaniques est régie principalement par le processus de dégazage des magmas. Nous avons reproduit expérimentalement les conditions de pression (P) et de température (T) subies par le magma au cours de sa remontée à la surface, afin d'étudier la vésiculation des volatils qui s'exsolvent du silicate liquide. Pour cela nous avons développé, utilisé et validé deux outils expérimentaux permettant l'observation en temps réel du dégazage magmatique. Nous avons utilisé des verres synthétiques hydratés, analogues de magmas rhyolitiques, mis en équilibre en P et T et auxquels nous avons fait subir des décompressions contrôlées provoquant le dégazage de l'eau. Une partie des expériences a été réalisée en cellule à enclume de diamants hydrothermale, permettant l'observation de la vésiculation, pour des conditions P-T de 8-12 kbar, 700-900°C et 7-18 %pds H2O dans le silicate liquide.Dans le cadre des améliorations technologiques associées à ce travail, nous avons participé à la mise au point de capteurs électriques implantés dans les diamants permettant la mesure de la température au plus près de l'échantillon. Les autres expériences ont été réalisées dans un autoclave à chauffage internet transparent permettant une observation de la chambre à échantillons pendant l'expérience, pour des conditions P-T de 1-3 kbar, 700-1000°C, avec 4-7 %pds H2O dans le liquide silicaté. Ces deux outils complémentaires nous ont permis de réaliser des expériences de décompression et d'observer in situ la nucléation, la croissance et la coalescence de bulles d'eau. Les résultats de ces expériences sont présentés et comparés. Leurs implications volcanologiques sont discutées.

Styles APA, Harvard, Vancouver, ISO, etc.

28

Aubaud, Cyril. « Processus de dégazage et sources mantelliques dans les magmas de type MORB et OIB : le carbone, l'eau et les gaz rares : aspects chimiques et isotopiques ». Paris 7, 2002. http://www.theses.fr/2002PA077011.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

29

Bouvier, Anne-Sophie. « Etude des magmas primaires de l'arc des Petites Antilles par l'analyse in situ des inclusions vitreuses ». Thesis, Nancy 1, 2008. http://www.theses.fr/2008NAN10071/document.

Texte intégral

Résumé :

Les laves de l’arc des Petites Antilles présentent une large gamme de compositions le long de l'arc et au sein d'un même centre volcanique. De précédentes études ont montré une variation de l'influence des fluides issus de la plaque océanique subductée le long de l’arc et au sein d’une même île. Cependant, la nature des fluides et l'importance de leurs contributions sont encore débattues. Afin d'apporter de nouvelles contraintes sur les conditions de genèse des magmas ainsi que sur l'influence et la nature des fluides issus du slab, des scories magnésiennes provenant de St. Vincent et Grenade, situées au sud de l’arc, ont été utilisés. Les compositions en éléments légers, traces et isotopes stables ont été déterminées par sonde ionique dans les inclusions vitreuses piégées dans les olivines, donnant un accès direct aux compositions des magmas primitifs, non affectés par les processus superficiels. La combinaison des différentes mesures a permis de mettre en évidence l’influence de trois sortes de fluides sur les sources mantelliques : 1- un fluide de compositions proche de celle de l’eau de mer, probablement relâché lors de la déshydratation du manteau serpentinisé entraîné en profondeur par le slab, 2- des fluides de déshydratation de la croûte océanique subductée et 3- des fluides issus de la déshydratation des sédiments. Ces fluides aqueux montrent des concentrations différentes en éléments dissous, reflétant la profondeur à laquelle ils sont extraits. L’ensemble des données révèle une genèse des magmas à plus forte profondeur et plus faible taux de fusion (7-15%) à Grenade, ceux de St. Vincent étant extraits à 1190-1220°C et 13-14 kbar avec un taux de fusion de 10-20%
The Lesser Antilles arc lavas display a large range of compositions. Previous studies have suggested a variable influence of fluids derived from the subducted oceanic lithosphere along the arc and within individual islands. The fluid contributions and their nature are still a matter of debate. In order to bring new constraints on magmagenesis conditions and on the influence and nature of fluids from the slab on the mantle source, high magnesia scoriae from St. Vincent and Grenada, in the south of the arc, have been used. Different analyses (light and trace elements, ?D, ??Li, ?11B, ?18O, ?34S) have been performed on olivine-hosted melt inclusions, using ion probe. Their study gives a direct access to the primitive magma compositions as yet unaffected by superficial processes. The association of several measurements permit three types of fluid components to be highlighted: 1- a seawater-like fluid, probably released by serpentinized mantle dehydration when it is pulled down by the slab, 2- fluids deriving from altered oceanic crust dehydration and 3- fluids issued from sediment dehydration. These aqueous fluids have different solute contents, reflecting their extraction depths. This dataset suggest a deeper genesis and lower partial melting rate (7-15%) for Grenada melts, St. Vincent melts being generated at 1190-1220°C, 13-14 kbar, from 10-20% partial melting

Styles APA, Harvard, Vancouver, ISO, etc.

30

Guo, Haihao [Verfasser], et Hans [Akademischer Betreuer] Keppler. « An Experimental Study on Volatiles and Metals in Fluids of Magma Chambers and Porphyry Ore Deposits / Haihao Guo ; Betreuer : Hans Keppler ». Bayreuth : Universität Bayreuth, 2018. http://d-nb.info/1156920647/34.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

31

Le, Voyer Marion. « Rôle des fluides dans la genèse des magmas d'arcs : analyses in situ des éléments volatils et des isotopes du bore dans les inclusions magmatiques des olivines primitives ». Phd thesis, Université Blaise Pascal - Clermont-Ferrand II, 2009. http://tel.archives-ouvertes.fr/tel-00453889.

Texte intégral

Résumé :

Les éléments volatils, principalement l'eau, sont enrichis dans les magmas d'arcs. Ils jouent un rôle prépondérant dans le magmatisme de zone de subduction, que ce soit en permettant la fusion du manteau ou en influençant l'explosivité des éruptions en surface. L'objectif de cette étude est la caractérisation (en éléments majeurs, traces, volatils et isotopes du bore) des liquides primaires des magmas d'arcs et de leurs sources, afin de discuter de l'influence des phases mobiles issues du slab dans leur genèse. L'approche adoptée est l'analyse des inclusions magmatiques piégées dans les olivines magnésiennes de quatre volcans répartis dans trois zones de subduction : Vulcano, dans l'arc Eolien (Italie), le Mont Shasta, dans l'arc des Cascades (Californie, Etats-Unis), le Pichincha et le Pan de Azucar, dans l'arc Equatorien. Les inclusions primaires étudiées contiennent des liquides basaltiques sous-saturés en silice, plus ou moins riches en CaO, dérivant d'une source mantellique veinée de zones riches en amphiboles (±clinopyroxène, ±phlogopite) et ayant subi un degré variable de métasomatisme. Leurs compositions en éléments traces illustrent l'enrichissement de leurs sources mantelliques par des composés mobiles issus du slab et de compositions contrastées. Il existe d'importantes variations des compositions en éléments volatils entre les inclusions provenant de plusieurs échantillons d'un même volcan (le Mont Shasta), celles provenant de plusieurs volcans d'une même zone de subduction (le Pichincha et le Pan de Azucar) ainsi qu'entre les inclusions des trois zones de subduction étudiées (arc Eolien, arc Equatorien et arc des Cascades). L'étude de l'évolution des teneurs en éléments volatils en fonction des pressions de saturation indique que seules les teneurs en Cl et F des inclusions magmatiques sont représentatives des teneurs du magma primitif. Le dégazage précoce et la formation de globules de sulfure affectent les teneurs en H2O, CO2 et S, qui peuvent être utilisées en tant qu'estimations minimales des teneurs des magmas primitifs. Les compositions en Cl des sources mantelliques des inclusions étudiées varient de 3±1 ppm à 450±125 ppm et celles en F varient de 16±6 ppm à 147±32 ppm (Cl/F de 0,2±0,1 à 3,6±1,2). L'association des rapports Cl/F des sources avec l'enrichissement en Nb (par rapport aux MORB) des inclusions et leurs valeurs isotopiques en bore suggère la participation de deux principaux composés mobiles dans la source de ces inclusions : (1) un liquide silicaté issu de la fusion des sédiments déshydratés (principal agent métasomatique de la source des inclusions du Pan de Azucar, qui possèdent des faibles δ11B ainsi qu'un fort enrichissement en Nb par rapport aux MORB) ; (2) un fluide aqueux formé lors de la déshydratation de la croûte océanique (principal agent métasomatique de la source des inclusions du Pichincha). Selon les propriétés physico-chimiques des différentes zones de subduction, ce fluide peut avoir les caractéristiques d'un fluide supercritique et être plus ou moins riche en éléments traces. Les compositions des inclusions de la Sommata (Italie) et de l'échantillon 95-15 du Mont Shasta montrent des enrichissements intermédiaires de leurs sources comparé à celles des inclusions du Pichincha et du Pan de Azucar. Leurs sources semblent avoir été métasomatisées par un mélange entre les deux composés métasomatiques décrits ci-dessus.

Styles APA, Harvard, Vancouver, ISO, etc.

32

Spilliaert, Nicolas. « DYNAMIQUES DE REMONTEE, DEGAZAGE ET ERUPTION DES MAGMAS BASALTIQUES RICHES EN VOLATILS :TRAÇAGE PAR LES INCLUSIONS VITREUSES ET MODELISATION DES PROCESSUS DANS LE CAS DE L'ETNA, 2000-2002 ». Phd thesis, Institut de physique du globe de paris - IPGP, 2006. http://tel.archives-ouvertes.fr/tel-00011876.

Texte intégral

Résumé :

Dans le cadre de cette thèse, nous avons cherché à mieux comprendre les processus de dégazage magmatique et les dynamismes éruptifs associés, à travers l'étude des roches totales et surtout celle, systématique, des inclusions vitreuses piégées par les olivines des produits explosifs de l'Etna. L'étude a porté plus particulièrement sur les basaltes et trachybasaltes émis lors des éruptions de flanc de 2001 et de 2002-2003, indépendantes des conduits centraux, et lors de trois épisodes de fontaines de lave au cratère Sud-Est, en 2000.
Nous avons constitué une base de données complète sur les éléments majeurs et les constituants volatils dissous (H2O, CO2, S, Cl et F) dans les magmas de l'Etna. Nous apportons des données nouvelles sur l'abondance en éléments volatils dissous (4%, dont une teneur en eau ~3,4%) dans le magma basaltique le plus primitif émis à l'Etna depuis 240 ans, et terme parental des trachybasaltes qui alimentent les éruptions actuelles du volcan. Nous proposons que l'évolution géochimique des magmas étnéens depuis 30 ans, résulte d'un mélange entre ce nouveau magma potassique et un terme trachybasaltique, mis en place dans les conduits avant les années 1970. L'analyse isotopique de l'eau et du soufre dissous dans les inclusions les plus primitives (delta(D) entre -120 et -90; ‰ ; delta(34S) = +2,4±0,4 ‰) conforte l'idée d'une source mantellique, de type OIB, peu affectée par la subduction ionienne toute proche, à l'encontre de certaines hypothèses préalablement formulées.
La détermination du CO2 et de l'eau dans les inclusions nous a permis (i) de contraindre les pressions de piégeage des liquides et d'exsolution du soufre, du chlore et du fluor, (ii) d'évaluer les profondeurs de transfert et de stockage du magma, (iii) de proposer un modèle d'évolution des rapports S/Cl et Cl/F dans la phase gazeuse dissoute et exsolvée en fonction de la pression, dans le cas des éruptions latérales et sommitales, et (iv) d'individualiser le rôle du globule de sulfure présent dans les magmas résidant superficiellement dans les conduits centraux.
Nous proposons ainsi que les éruptions de flanc en 2001 et 2002 résultent de la remontée et du dégazage, en système fermé, du magma basaltique à trachybasaltique, coexistant avec une phase gazeuse déjà exsolvée. Le magma le plus primitif, remonte d'une profondeur >10 km (sous le niveau de la mer), et est extrudé lors des fontaines de laves. Le plus gros volume de laves produit dérive du transfert du magma trachybasaltique, légèrement plus différencié et stocké à 5±1 km. Lors de son stockage temporaire, ce magma s'appauvrit en eau, en se rééquilibrant avec une phase gazeuse riche en CO2, d'origine profonde. La déshydratation partielle d'un magma, stocké dans les conduits, en relation avec un flux de gaz persistant, riche en CO2, est probablement un processus fréquent à l'Etna et dans d'autres volcans basaltiques.
L'évolution modélisée des rapports S/Cl et Cl/F dans la phase gazeuse confirme un dégazage dominant en système fermé en 2001 et 2002. Les valeurs calculées des rapports molaires S/Cl des gaz à la surface de 5,4 à 3,7 et Cl/F de ~2, dépendent de la cinétique de dégazage syn-éruptif du chlore, et sont en parfait accord avec les mesures in situ effectuées par télédétection, au cours de la même période éruptive. Toute ségrégation de bulles de gaz en profondeur se traduit par des rapports S/Cl plus élevés dans la phase gazeuse. Ceci est également vérifié par la modélisation en système fermé du dégazage du magma stagnant superficiellement dans les conduits centraux et saturé vis-à-vis du globule de sulfure. La modélisation en pression de l'évolution de ce rapport permet donc de contraindre les profondeurs d'accumulation et de transfert différentiel des bulles. La valeur des rapports S/Cl et Cl/F dans les gaz ainsi que la nature des produits solides associés apportent de fortes contraintes sur les mécanismes à l'origine des fontaines de laves.
Enfin, l'activité de dégazage persistant aux cratères, impliquant une convection efficace dans les conduits, suggèrerait la remontée de magma riche en éléments volatils jusqu'à de faibles profondeurs (≤ 1 km sous les cratères), et le recyclage du magma dégazé, afin d'alimenter les flux gazeux excédentaires.
Notre modélisation offre ainsi un cadre général d'interprétation de la composition des émissions gazeuses, et contribue à une meilleure compréhension des processus de dégazage des magmas basaltiques, riches en éléments volatils, à l'Etna.

Styles APA, Harvard, Vancouver, ISO, etc.

33

Spilliaert, Nicolas. « Dynamiques de remontée, dégazage et éruption des magmas basaltiques riches en volatils : Traçage par les inclusions vitreuses et modélisation des processus dans le cas de l'Etna, 2000-2002 ». Paris, Institut de physique du globe, 2006. http://www.theses.fr/2006GLOB0022.

Texte intégral

Résumé :

Dans le cadre de cette thèse, nous avons cherché à mieux comprendre les processus de dégazage magmatique et les dynamismes éruptifs associés, à travers l’étude des roches totales et surtout celle, systématique, des inclusions vitreuses piégées par les olivines des produits explosifs de l’Etna. L’étude a porté plus particulièrement sur les basaltes et trachybasaltes émis lors des éruptions de flanc de 2001 et de 2002-2003, indépendantes des conduits centraux, et lors de trois épisodes de fontaines de lave au cratère Sud-Est, en 2000. Nous avons constitué une base de données complète sur les éléments majeurs et les constituants volatils dissous (H2O, CO2, S, Cl et F) dans les magmas de l’Etna. Nous apportons des données nouvelles sur l’abondance en éléments volatils dissous (4%, dont une teneur en eau ≥3,4%) dans le magma basaltique le plus primitif émis à l’Etna depuis 140 ans, et terme parental des trachybasaltes qui alimentent les éruptions actuelles du volcan. Nous proposons que l’évolution géochimique des magmas étnéens depuis 30 ans, résulte d’un mélange entre ce nouveau magma potassique et un terme trachybasaltique, mis en place dans les conduits avant les années 1970. L’analyse isotopique de l’eau et du soufre dissous dans les inclusions les plus primitives (δD entre -120 et -90; ‰ ; δ34S = +2,4±0,4 ‰) conforte l’idée d’une source mantellique, de type OIB, peu affectée par la subduction ionienne toute proche, à l’encontre de certaines hypothèses préalablement formulées. La détermination du CO2 et de l’eau dans les inclusions nous a permis (i) de contraindre les pressions de piégeage des liquides et d’exsolution du soufre, du chlore et du fluor, (ii) d’évaluer les profondeurs de transfert et de stockage du magma, (iii) de proposer un modèle d’évolution des rapports S/Cl et Cl/F dans la phase gazeuse dissoute et exsolvée en fonction de la pression, dans le cas des éruptions latérales et sommitales, et (iv) d’individualiser le rôle du globule de sulfure présent dans les magmas résidant superficiellement dans les conduits centraux. Nous proposons ainsi que les éruptions de flanc en 2001 et 2002 résultent de la remontée et du dégazage, en système fermé, du magma basaltique à trachybasaltique, coexistant avec une phase gazeuse déjà exsolvée. Le magma le plus primitif, remonte d’une profondeur >10 km (sous le niveau de la mer), et est extrudé lors des fontaines de laves. Le plus gros volume de laves produit dérive du transfert du magma trachybasaltique, légèrement plus différencié et stocké à 5±1 km. Lors de son stockage temporaire, ce magma s’appauvrit en eau, en se rééquilibrant avec une phase gazeuse riche en CO2, d’origine profonde. La déshydratation partielle d’un magma, stocké dans les conduits, en relation avec un flux de gaz persistant, riche en CO2, est probablement un processus fréquent à l’Etna et dans d’autres volcans basaltiques. L’évolution modélisée des rapports S/Cl et Cl/F dans la phase gazeuse confirme un dégazage dominant en système fermé en 2001 et 2002. Les valeurs calculées des rapports molaires S/Cl des gaz à la surface de 5,4 à 3,7 et Cl/F de ~2, dépendent de la cinétique de dégazage syn-éruptif du chlore, et sont en parfait accord avec les mesures in situ effectuées par télédétection, au cours de la même période éruptive. Toute ségrégation de bulles de gaz en profondeur se traduit par des rapports S/Cl plus élevés dans la phase gazeuse. Ceci est également vérifié par la modélisation en système fermé du dégazage du magma stagnant superficiellement dans les conduits centraux et saturé vis-à-vis du globule de sulfure. La modélisation en pression de l’évolution de ce rapport permet donc de contraindre les profondeurs d’accumulation et de transfert différentiel des bulles. La valeur des rapports S/Cl et Cl/F dans les gaz ainsi que la nature des produits solides associés apportent de fortes contraintes sur les mécanismes à l’origine des fontaines de laves. Enfin, l’activité de dégazage persistant aux cratères, impliquant une convection efficace dans les conduits, suggèrerait la remontée de magma riche en éléments volatils jusqu’à de faibles profondeurs (≤ 1 km sous les cratères), et le recyclage du magma dégazé, afin d’alimenter les flux gazeux excédentaires. Notre modélisation offre ainsi un cadre général d’interprétation de la composition des émissions gazeuses, et contribue à une meilleure compréhension des processus de dégazage des magmas basaltiques, riches en éléments volatils, à l’Etna
This study is aimed at better understanding magma degassing processes and associated eruptive dynamics through the study of the bulk rocks and mainly of olivine-hosted melt inclusions from explosive products of Mount Etna. We particularly focussed on the 2001 and 2002 flank eruptions that resulted from dyke intrusions, independent of the central conduits, and on three lava fountains at South-East summit crater, in 2000. We acquired a complete data set on major elements and volatile contents (H2O, CO2, S, Cl and F) of Etna magmas. We report new data on the amount of volatiles (4 wt%, among which ≥3. 4 wt% H2O) dissolved in the most primitive K-rich basaltic melt erupted at Mount Etna for the last 140 years. This basalt is actually the parental melt of the trachybasalts erupted during the recent volcanic activity. We also argue that the geochemical evolution of etnean lavas for the last 30 years, results from the mixing between the new K-rich melt and K-poorer trachybasalts, emplaced in the feeding system prior to 1970. Isotopic analysis of water and sulphur in the most primitive melt inclusions (δD between -120 and -90; ‰ ; δ34S = +2,4±0,4 ‰) reinforces the idea of an OIB-type mantle source and contradicts the hypothesis of its contamination by fluids derived from the Ionian subduction, as previously suggested. The systematic determination of CO2 and H2O contents of melt inclusions allow us (i) to provide constraints on melt entrapment and S, Cl and F initial exsolution pressures, (ii) to assess the depths of magma transfer and ponding, (iii) to propose a pressure-related model of the evolution of the dissolved and exsolved gas phase, and (iv) to evaluate the effect of the sulphide immiscible liquid on the sulphur degassing path. We propose that the 2001 and 2002 flank eruptions were sustained by closed system ascent and degassing of basaltic to trachybasaltic magmas. The most primitive magmas rose from at least ~10 km b. S. L. And sustained the powerful lava fountains that occurred in July 2001 and October 2002. Most of the lavas emitted in 2001 and 2002 derived from trachybasaltic magmas, ponding at 5±1 km b. S. L. , that were partially dehydrated because of their flushing by a CO2-rich gas phase of deep derivation. Such a process could be frequent at Etna and most likely at basaltic volcanoes. The S/Cl molar ratio in the associated gas phase is computed to be of 5. 4 and 3. 7, depend on the degassing dynamics upon eruption. These calculated values and those of the Cl/F (2) and S/CF (9) ratios confirm a dominant closed system magma ascent and degassing mechanism. They are in good agreement with those directly measured by teledetection during the 2001 and 2002 flank eruptions. Furthermore, any gas/melt separation occurring at greater depth would result in higher S/Cl ratios in the gas phase. This also applies to magmas, already saturated with sulphide globule, that are stored at shallow depths in the central conduits and degas under closed system conditions. Therefore, the modelled evolution of S/Cl and Cl/F ratios, both in the melt and the gas phase, gives access to the depths of gas segregation. The S/Cl and Cl/F ratios in the gas emission at the surface, along with the chemistry of associated solid products, bring strong constraints on the different mechanisms at the origin of lava fountains. Finally, steady state summit degassing, involving convective overturn in conduits, would imply ascent of volatile-rich magma until shallow depth (≤ 1 km under the craters), and thus the drain-back of the shallow degassed magma, in order to supply the excess gas flux at Mt Etna. As a whole, our modelling offers a general background to interpret gas emissions composition and so to better understand the different degassing processes that occur during the ascent of etnean volatile-rich basaltic melts

Styles APA, Harvard, Vancouver, ISO, etc.

34

Travers, Metrich Nicole. « Mécanismes d'évolution à l'origine des magmas potassiques d'Italie Centrale et Méridionale : exemples du Mt Somma-Vésuve, des champs phlégréens et de l'île de Ventotène ». Paris 11, 1985. http://www.theses.fr/1985PA112350.

Texte intégral

Résumé :

Depuis un million d’années, les magmas potassiques sont émis sur la marge tyrrhénienne des Apennins centraux et méridionaux à la faveur de trois systèmes tectoniques principaux (NW-SE, NE-SW, E-W). Ce mémoire traite de l’évolution intracrustale des liquides magmatiques dans les cas du Mt Somma Vésuve, des Champs Phlégréens et de l’île de Ventotène, caractérisés par une large gamme de magmas potassiques à fortement potassiques et sous-saturés en silice. Pour ce faire, nous avons diversifié les méthodes d’investigation en nous appuyant sur une histoire volcanologique précise des appareils, en développant l’étude minéralogique et géochimique des laves et des ponces ainsi que l’étude chimique et thermométrique des inclusions vitreuses présentes dans les minéraux des roches. Nous avons ainsi privilégié l’aspect concernant les conditions de cristallisation (variations chimiques et minéralogiques, gradients thermiques, nature et importance de la phase volatile, rôle de l’encaissant sédimentaire). Un processus dominant de différenciation par cristallisation fractionnée peut être invoqué pour les trois ensembles. Pourtant chacun des systèmes connait une évolution qui lui est spécifique, reflétant ainsi la diversité des magmas initiaux. Pour les strato-volcans, comme le Mt Somma Vésuve ou Ventotène, caractérisés par une activité à la fois de type effusif et explosif, les éruptions pliniennes ou subpliniennes sont l’expression de magmas différenciés au sein de réservoirs superficiels de petite taille et localisés dans un horizon sédimentaire. Les évidences d’une contamination des liquides magmatiques par les roches encaissantes restent limitées. En revanche, l’encaissant va favoriser le processus de nucléation – cristallisation qui se traduit par l’existence de cumulats et d’enclaves réactionnelles. Les produits volcaniques des Champs Phlégréens sont essentiellement des pyroclautites de composition trachytique dont l’évolution s’intègre dans le modèle d’un réservoir d’importantes dimensions. L’hypothèse de la variation du degré de fusion d’une source mantellique hydratée, à l’origine des magmas potassiques et sous-saturés en silice du Somma Vésuve et ceux (basaltiques) de Ventotène est proposée sur la base des données géochimiques
Since one million years, potassic to highly potassic magmas have erupted along the Tyrrhenian margin of the Central and Southern Apennins, through three main tectonic systems (NW-SE, NE-SW, E-W). The present work deals with the magmatic liquids intracrustale evolution of the Mt Somma Vesuve and the Phlegrean Fields and Ventotene Island volcanoes. In this regard, we have diversified the studying methods, basing ourselves on the accurate volcanic history of the apparatus and showing a special interest in the crystallization conditions (chemical and mineralogical variations, thermal gradients, nature and importance of the volatile phase, role of the surrounding sedimentary rocks). Besides the fact that a crystal fractionation process prevails, each system has its own specific evolution, as an indication of the primary magmas variety. In the case of stratovolcanoes, as Mt Somma Vesuve or Ventotene, which are characterized by an activity both effusive and explosive, the plinian and subplinian eruptions reveal a differentiation of the magmas in small and superficial chambers surrounded by sedimentary rocks. Little evidence can be given of contamination of the liquids by these enclosing rocks. On the other hand, the country rock will emphasize the nucleation-crystallization process, leading to cumulate and reactional xenoliths. The Phlegrean Fields volcanic products are mostly pyroclastites of trachytic composition. Their evolution corresponds to that of a great magma chamber probably thermically buffered. Finally, the Campanean magmas (including those of Ventotene) are shown to the possibly originated from partial fusion of hydreous mantle. This hypothesis is based on the Th/Ta ratio (ranging from 7. 5 to 11. 4), these strongly hygromagmaphile elements being considered as source markers

Styles APA, Harvard, Vancouver, ISO, etc.

35

Husen, Anika [Verfasser]. « Magma differentiation processes and volatile contents beneath the Shatsky Rise oceanic plateau : constraints from mineral, glass and melt inclusion compositions combined with thermodynamic and experimental modeling / Anika Husen ». Hannover : Technische Informationsbibliothek und Universitätsbibliothek Hannover (TIB), 2014. http://d-nb.info/1065275552/34.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

36

Moune, Severine. « Volatils mineurs (S, Cl, F) et éléments traces dans les magmas pré-éruptifs et les gaz volcaniques. Etude des processus de dégazage magmatique sur les volcans Hekla (Islande) et Masaya (Nicaragua) ». Phd thesis, Université Blaise Pascal - Clermont-Ferrand II, 2005. http://tel.archives-ouvertes.fr/tel-00011542.

Texte intégral

Résumé :

L'axe principal de cette thèse est la caractérisation des processus de dégazage magmatique des éléments traces, du soufre et des halogènes de deux volcans actifs : Hekla (Islande) et Masaya (Nicaragua).
Une étude sur les inclusions magmatiques (MIs) a permis de suivre l'évolution des volatils dissous dans le système volcanique d'Hekla au cours de la différenciation magmatique (cristallisation fractionnée). Ceci a permis d'estimer les concentrations en volatils dissous "attendues" dans le liquide pré-éruptif. Cette approche permet donc de ne pas sous-estimer les concentrations des liquides piégés dans les MIs et améliore ainsi les contraintes sur la masse de volatils émise dans l'atmosphère. Cette étude indique que, lors de l'éruption de février 2000, Hekla a émis dans l'atmosphère 0.1 Mt de HCl, 0.2 Mt de HF et 3.8 Mt de SO2. La chimie de la phase sub-Plinienne de cette éruption a été étudiée, de façon plus approfondie, grâce aux averses neigeuses qui ont traversé le panache volcanique. L'étude de ces neiges a montré que l'enrichissement des éléments volatils est lié à un processus de dégazage sous forme de chlorures, fluorures et sulfates. En revanche, l'enrichissement des éléments réfractaires est expliqué par un processus de dissolution non-stoechiométrique des téphras par la phase gazeuse riche en fluor au sein du panache éruptif.
Une étude basée sur les MIs a permis de confirmer la théorie de Walker et al. (1993) selon laquelle la différenciation des magmas tholéiitiques du Masaya se produit à basse pression à partir d'un magma relativement "sec" de composition homogène dans le temps. La caractérisation physico-chimique des aérosols par MEB et la chimie de la phase éruptive du volcan Masaya suggèrent que la plupart des éléments traces sont dégazés sous forme de chlorures, mais aussi sous forme de sulfates et chloro-sulfates. De plus, la quantification des flux de matière a montré que le dégazage au Masaya est une source importante de pollution atmosphérique.

Styles APA, Harvard, Vancouver, ISO, etc.

37

Colin, Aurélia. « Contraintes sur les processus de dégazage des dorsales océaniques par la géochimie des volatils et la pétrologie des laves basaltiques ». Thesis, Vandoeuvre-les-Nancy, INPL, 2010. http://www.theses.fr/2010INPL083N/document.

Texte intégral

Résumé :

Afin de préciser l'origine des volatils terrestres et les flux actuels et passés vers l’atmosphère, de nombreuses études s’intéressent à la composition du manteau. Ce réservoir est échantillonné naturellement lors des éruptions volcaniques, mais une grande partie des gaz est alors émise dans l'atmosphère, de sorte que la composition des volatils du manteau reste peu contrainte. Nous cherchons à préciser les mécanismes de dégazage sous les dorsales océaniques afin de corriger ces fractionnements. L'analyse (He-Ne-Ar-CO2) de verres basaltiques issus de la dorsale des Galápagos, dans la zone d'influence du point chaud des Galápagos, montre que la composition en volatils des laves s'explique par distillation de Rayleigh d'une source unique. Cette source est distincte de celle du point chaud (isotopes du néon), impliquant un dégazage en profondeur du panache ou une hétérogénéité spatiale de sa composition.Plusieurs verres volcaniques issus de la dorsale Atlantique et Est Pacifique ont été imagés par micro-tomographie aux rayons X. L'étude met en évidence des mécanismes de nucléation et de croissance des bulles différents sous les deux dorsales. De la convection en périphérie de la chambre magmatique avant l’éruption a été mise en évidence par l’étude pétrologique des verres. Les vésicules imagées ont ensuite été ouvertes individuellement sous vide par ablation laser et analysées (CO2, 4He, isotopes de l'argon). La composition des bulles est hétérogène dans certains échantillons et compatible avec une distillation de Rayleigh. Les tendances de dégazage obtenues permettent d'obtenir localement la composition de la source mantellique, qui est hétérogène.L'étude permet également d'appréhender l'hétérogénéité des rapports 40Ar/36Ar dans les chambres magmatiques par la technique d’ablation laser qui diminue la contamination atmosphérique par rapport à la technique classique de broyage
The composition of mantle volatiles is related to the origin of Earth's volatiles and to the past and present volatile fluxes to the atmosphere. Although this reservoir is naturally sampled during volcanic eruptions, most of the volatiles are lost to the atmosphere during this event, thus the composition of mantle volatiles is still uncertain. We try here to precise the processes of degassing below mid-oceanic ridges to correct the lava compositions for degassing.The He-Ne-Ar-CO2 analyses of basaltic glasses sampled along the Galapagos Spreading Center, in the area of influence of the Galapagos hotspot, show that the volatile composition of lavas is fully explained by a Rayleigh distillation of a unique source distinct from the plume source. These results imply that the plume degasses at depth or is heterogeneous.Several volcanic glasses from Mid-Atlantic ridge and East Pacific Rise have been imaged by X-rays microtomography. The mechanisms of vesicle nucleation and growth appear to be different below the two ridges. A step of convection at the magma body margin has been evidenced by the petrologic study of the glasses. Imaged vesicles have been subsequently opened under vacuum by laser ablation and analysed (CO2, 4He, argon isotopes). We observe, depending on the samples, either a single composition for all bubbles, or variations in composition between bubbles consistent with a trend of equilibrium degassing in an open system. The trends of degassing allow extrapolating locally to the volatile composition of the mantle source, which is heterogeneous. We also studied the heterogeneity of 40Ar/36Ar ratios in magmatic chambers using the laser opening method, which lowers the contribution of atmospheric gases compared to the classical crushing method

Styles APA, Harvard, Vancouver, ISO, etc.

38

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

Texte intégral

Résumé :

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)

Styles APA, Harvard, Vancouver, ISO, etc.

39

Sosa, Ceballos Giovanni 1975. « Evolution of Plinian magmas from Popocatépetl Volcano, México ». Thesis, 2011. http://hdl.handle.net/2152/26905.

Texte intégral

Résumé :

Fractional crystallization, magma mixing, assimilation of continental crust, and how those processes modify volatile budgets, control the evolution of magma. As a consequence, the understanding of these processes, their magnitudes, and timescales is critical for interpreting ancient magma systems, their eruptions, and the potential future volcanic activity. In this dissertation I present the results of three projects. The first explores how magmatic processes affect magma reservoirs and eruption dynamics. The second explores where in the storage system and how often these processes occur. The third explores how volatile budgets are modified by processes such as crystallization, mixing, and assimilation. Volcán Popocatépetl (central México) erupted ~14100 14C yr BP producing the Tutti Frutti Plinian Eruption (TFPE). The eruption tapped two different silicic magmas that mixed just prior and during the eruption. The influx of mass and volatiles generated during the mixing of both magmas overpressured the reservoir, which was weakened at the top. The weakened reservoir relaxed while magma was tapped and collapsed to form a caldera at the surface. Although it is known that fractional crystallization, mixing, and assimilation can greatly modify magmas, the frequency and intensity of these events is not known. I investigated the magmatic processes responsible for the evolution of magmas erupted during five Plinian events of Popocatépetl volcano. Results show that during the last 23 ky magma was stored in two different zones, and was variably modified by replenishments of mafic magma. Interestingly, little evidence for large mafic inputs triggering explosive eruptions was found. Each of these processes alters the abundances of volatiles and introduces different types of volatiles to the system. Hence, the volatile budget of magma can have a rich and complex history. To investigate how volatile budgets evolve in active magma systems, I analyzed the abundances of volatiles (H2O, CO2, F, Cl, and S) in numerous glass inclusions trapped in phenocrysts. Results show that the magmas that produced the last five Plinian eruptions at Popocatépetl volcano evolved by crystallization and magma mixing, assimilation of the local carbonate basement is not chemically appreciable. Mixing with mafic magmas added substantial CO2 and S to the system, dewatered the magma, yet produced little change in the F contents of the magmas.
text

Styles APA, Harvard, Vancouver, ISO, etc.

40

MacKenzie, Jason. « Volatile metal mobility and fluid/melt partitioning : Experimental constraints and applications to degassing magmas ». Thesis, 2008. http://hdl.handle.net/1828/1316.

Texte intégral

Résumé :

Volatile trace metals are variably enriched in volcanic gases. Metal concentrations in sub-aerially erupted magmas are also depleted in many of these metals. The causes of variable metal enrichment in volcanic gasses, however, remain enigmatic. The objective of this work is to place experimental constraints on kinetic and thermodynamic factors that influence the concentrations of trace metals in volcanic gases. To measure metal mobility in silicate melts, Pt crucibles packed with metal doped glasses of broadly basaltic composition were equilibrated with air and mixed gases at atmospheric pressure. The metals in the melt diffused to the gas/melt interface where they were released as a volatile species. The experiments produced concentration-distance profiles from which diffusivity was derived. Experiments were also conducted in a piston-cylinder apparatus at 1 GPa pressure. In these experiments, melts were equilibrated with Cl-bearing fluids at high temperature and pressure. At equilibrium, trace metals partitioned between the melt and fluid phase as a function of temperature and fluid composition. The diffusivity of Re in melts of natural basalt, andesite and a synthetic composition in the CaO-MgO-Al2O3-SiO2 (CMAS) system has been investigated at 0.1 MPa and 1250-1350C over a range of fO2 conditions from log fO2 = -10 to –0.68. Re diffusivity in natural basalt at 1300C in air is logDRe = -7.2  0.3 cm2/sec and increases to logDRe = -6.6 0.3 cm2/sec when trace amounts of Cl were added to the starting material. At fO2 conditions below the nickel-nickel oxide (NNO) buffer Re diffusivity decreases to logDRereducing = -7.60.2 cm2/sec and to logDReandesite = -8.4  0.2 cm2/sec in andesite melt. Cd, Re, Tl, Pb, Sb and Te diffusivity in CMAS and Na2O-MgO-Al2O3-SiO2 (NMAS) melts were also determined at 0.1 MPa and 1200-1350C. In the CMAS composition at 1300C, the fastest diffusing element was Cd having a logDCd = -6.5  0.2. The slowest element was Re with logDRe = -7.5  0.3. Diffusivities of Sb, Te, Pb and Tl have intermediate values where logDSb = -7.1  0.1, logDTe = -7.2  0.3, logDPb = -7.1  0.2, logDTl = -7.0  0.2 cm2/sec. In the NMAS composition, logDRe = -6.5  0.2, logDSb = -6.0  0.2, logDPb = -6.1  0.1, logDTl = -5.8  0.2 cm2/sec. Fluid/melt partition coefficients ( ) of Re, Mo, W, Tl and Pb between fluid (H2O + Cl) and a haplobasaltic melt in the CMAS system were measured between 1200 and 1400°C at 1 GPa and fluid chlorine molarities from 7.7 to 27 mol/L. At 1300°C and fluid molarity of 7.7 mol/L, = 9.8±1.8, = 11.8±1.6, = 3.7±1.6, = 4.5±1.4 and = 2.4 ±1.8. Both Mo and Re were shown to partition most strongly into the fluid at all temperatures and fluid chlorinities. Differences in diffusivity of volatile heavy metal ions to a lead to significant fractionation between these metals in magmas during degassing. Given the observed differences in Cd and Re diffusivities, an increase in the normalized Cd/Re ratio in the gas phase with increasing bubble growth rate is predicted. Monitoring of the Cd/Re ratios in aerosols from degassing volcanoes may provide a tool for predicting volcanic eruption. Modeling of Re using the values measured here support the contention that subaerial degassing is the cause of lower Re concentrations in arc-type and ocean island basalts compared to mid-ocean ridge basalts. The model results were also compared with emanation coefficients for trace metals from natural volcanoes. The magnitudes of the modeled Re/Tl and Re/Pb in fluids at 1300C and the lowest fluid chlorinities were less than that observed from their emanation coefficients. Re and Pb are more sensitive to fluid chlorinity than Tl. The ratios of Re/Tl and Re/Pb expected from emanation coefficients are closely matched if partitioning values for experiments having fluid chlorinities of ~16-20 MCl at 1300C are used.

Styles APA, Harvard, Vancouver, ISO, etc.

41

Lester, GREGORY W. « An experimental study of liquid-phase separation in the systems Fe2SiO4-Fe3O4-KAlSi2O6-SiO2-H2O, Fe3O4-KAlSi2O6-SiO2-H2O and Fe3O4-Fe2O3-KAlSi2O6-SiO2-H2O with or without P, S, F, Cl or Ca0.5Na0.5Al1.5Si2.5O8 : Implications for immiscibility in volatile-rich natural magmas ». Thesis, 2012. http://hdl.handle.net/1974/7054.

Texte intégral

Résumé :

Abstract Isobaric (200 MPa) experiments have been performed to investigate the effects of H2O alone or in combination with P, S, F or Cl on the phase relations and elemental and oxygen isotopic partitioning between immiscible silicate melts in the systems Fe2SiO4-Fe3O4-KAlSi2O6-SiO2, Fe3O4-KAlSi2O6-SiO2 and Fe3O4-Fe2O3-KAlSi2O6-SiO2 +/- plagioclase (An50). Experiments were heated in a newly-designed rapid-quench internally-heated pressure vessel at 1075, 1150 or 1200 oC for 2 hours. Water alone or in combination with P, S, or F significantly increases the temperature and composition range of two-liquid fields at fO2= NNO and MH buffers. Water-induced suppression of liquidus temperatures, considered with the effects of pressure on two-liquid fields stability in silicate melts, suggests that liquid phase separation may occur in some volatile-rich silicate magmas at pressures up to 2GPa. Two-liquid partition coefficients for Fe, Si, P and S correlate well with the degree of polymerization of the SiO2-rich conjugate melts and the data can be applied to assess the involvement of liquid-phase separation in the genesis of coexisting volatile-rich magmas. The partitioning of trace concentrations of selected HFSE, REE and transition elements between immiscible experimental volatile-rich melts at 1200 oC, 200 MPa has been determined at QFM, NNO and MH oxygen buffers. Water generally increases the partitioning of HFSE, REE and transition elements into the Fe-rich melt. Water alone, or combined with P or S, produces nearly parallel partitioning trends for HFSE and REE. Absolute partitioning values of transition elements are strongly dependent on the network-modifier composition of the melt. 18O in experimental immiscible melts with H2O or H2O and P or S partitions preferentially into the felsic conjugate melt (δ18O felsic melt- δ18O mafic melt values range from 0.4 to 0.8 permil) consistent with observations in anhydrous immiscible silicate melts. The expansion of the P-T-X-fO2 stability ranges of two- or three-liquid fields observed in the experimental melts demonstrates that liquid-immiscibility may be an important process in the evolution of some volatile-rich natural magmas. The results support an immiscible petrogenetic origin for some iron-oxide dominated, Kiruna-type, ore-deposits.
Thesis (Ph.D, Geological Sciences & Geological Engineering) -- Queen's University, 2012-04-10 15:06:35.797

Styles APA, Harvard, Vancouver, ISO, etc.

42

Johnson, Angela D. « The degassing behavior of volatile heavy metals in subaerially erupted magmas and their chemical diffusion in silicate melts ». Thesis, 2009. http://hdl.handle.net/1828/2014.

Texte intégral

Résumé :

Volatile heavy metals are liberated from magmas during eruptive and passively degassing volcanic activity. Volcanic emanations have been estimated to contribute 20-40% of volatile elements such as Bi, Pb, As or Sb, and up to 40-50 % of Cd and Hg annually (Nriagu, 1989). Some workers, however, believe these ranges are too high (Hinkley, 1999) or too low (Zreda-Gostynska and Kyle, 1997) leading to considerable differences in global inventory budgets of these metals and the degree to which they load the atmosphere. The objective of this work is to investigate the behavior of volatile heavy metals such as Au, Tl, As, Pb etc. in subaerially erupted magmas and experimentally in silicate melts. Analysis of natural pumice samples confirm the futile, sporadic nature of Hg and associated heavy metals, suggesting these metals are fully degassed prior to deposition. Diffusion experiments were conducted in natural basalt, dacite and synthetic rhyolite (Ab-Or-Qz minimum eutectic) over a range of temperatures (1200 – 1430 °C) at 0.1 MPa. Starting compositions were doped with a heavy metal cocktail (Bi, Pb, Tl, Au, Re, Sb, Sn, Cd, Mo, As, Cu) and loaded into open top Pt capsules. One set of experiments examined the effect of melt composition (polymerization) on element diffusion, and the second investigated the effects of ligands on diffusion by adding known concentrations of Cl and S. During experiments of varying duration, concentration gradients arose in the volatile trace metals due to their varying volatility, as measured (normal to the melt/gas interface) by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) in quenched glasses. Diffusion profiles followed an Arrhenius relationship from which diffusion coefficients (D) and activation energies (Ea) were obtained for Au, Tl, As, Cd, Re, Pb and Bi (in decreasing order of volatility). Results show Au and Tl are the most volatile in dacite and rhyolite yielding LogDDac Au = -10.7 ± 0.1 m2/s and LogDDac Tl = -10.9 ± 0.1 m2/s in dacite, and LogDRhy Au = -10.9 ± 0.1 m2/s and LogDRhy Tl = -11.3 ± 0.3 m2/s in rhyolite respectively. The D for Au could not be measured in basalt but Tl was the fastest diffusing species LogDBas Tl = -10.8 ± 0.2 m2/s. Ligands Cl and S were shown to increase the volatilities of all metals, with S having a more profound effect. Diffusivities were applied to a simple 1D bubble growth model (Smith 1955). Model results indicate diffusion coefficients play a major role in metal fractionation processes occurring at depths that ultimately dictate what metal ratios are measured at the surface of volcanoes.

Styles APA, Harvard, Vancouver, ISO, etc.

43

Barth, Anna Claire. « Ascent rates and volatiles of explosive basaltic volcanism ». Thesis, 2021. https://doi.org/10.7916/d8-zkzt-a130.

Texte intégral

Résumé :

Explosive volcanic eruptions are propelled to the surface by the exsolution of vapour bubbles from magma due to decompression. A long-held view is that the amount of H₂O dissolved in the magma at depth controls the intensity of an explosive eruption. Growing evidence from studies reporting H₂O concentrations of melt inclusions (MIs) do not support this view. Instead, the rate at which magma ascends to the surface may play an important role in modulating the eruption style. Slow magma ascent allows the vapour bubbles to rise ahead of the magma, thereby diffusing the driving force for an explosive eruption, whereas for fast magma ascent, the bubbles remain essentially trapped within the magma, causing acceleration and the potential for an explosive eruption. Chapter 1 presents a new modelling approach to constrain magma decompression rate based on the incomplete diffusive re-equilibration of H₂O in olivine-hosted melt inclusions. We apply this chronometer to two contrasting eruptions at Cerro Negro volcano in Nicaragua: the 1992 VEI 3 and 1995 VEI 2 eruptions. Both eruptions have the same basaltic composition (SiO₂ ∼ 50 wt%) and maximum volatile concentrations (H₂O ∼ 4.7 wt%). However, MIs from the less explosive 1995 eruption appear to have experienced more water loss compared to those from the 1992 eruption, which is consistent with slower magma ascent. We present a parameterization of the numerical diffusion model in chapter 2, which significantly reduces the calculation time, facilitating the use of Monte Carlo simulations to evaluate uncertainties. We use this parameterization to create a regime diagram that can be used to guide when melt inclusions may be used as magma hygrometers and when they are better suited to act as magma speedometers. We develop diagnostic tools to recognize where and when water loss has occurred in a magma’s ascent history, and we outline quantitative tools that may be used to restore the primary and/or pre-eruptive water content. We find that one of the largest sources of uncertainty in modelling diffusive re-equilibration of H₂O in MIs and olivines is the diffusivity of H+ in olivine. We present new experimental constraints on H+ diffusivity in olivines from Cerro Negro (1992 eruption) and Etna (3930 BP ‘Fall Stratified’ eruption) (chapters 1 and 3, respectively). Our results show that H+ diffusion is highly anisotropic with the diffusivity along the [100] direction more than an order of magnitude faster than along [010] or [001], implying a large role for the ‘proton-polaron’ diffusion mechanism, which shares this anisotropy. We also find that the lower forsterite (Fo ~ 80) olivines from Cerro Negro have significantly faster H+ diffusivity than higher forsterite (Fo ~ 90) olivines from Etna. The results for Etna agree well with other estimates on high forsterite olivines from San Carlos and Kilauea, suggesting that the Fe content of the olivine strongly affects the H+ diffusivity. In chapter 4, we apply the methods from the first three chapters to an unusually explosive eruption of picritic magma at Etna, Sicily in 3930 BP (termed the ‘Fall Stratified’ eruption). MIs from this eruption show limited evidence for water loss and so cannot be modelled to determine decompression rate. Instead, we model H+ diffusion profiles within the olivine crystals themselves and determine rapid ascent rates of ~15 m/s. We perform rehomogenization experiments on the MIs to accurately assess their pre-eruptive CO₂ concentrations, and find nearly 1 wt.% CO₂. Solubility modelling indicates that these MIs must have been trapped at near Moho depths (24–30 km). The magma’s high CO₂ concentration and deep initial pressures may have been responsible for the magma’s rapid ascent, which ultimately led to its great eruption intensity.

Styles APA, Harvard, Vancouver, ISO, etc.

44

Clark, Heather A. « Evolution Of Volatile Content Of The Parent Magma Of The 1875 Eruption Of Askja Volcano, Iceland ». 2012. https://scholarworks.umass.edu/theses/794.

Texte intégral

Résumé :

The bulk of the eruption of Askja in north central Iceland on March 28-29 1875 consisted of a plinian eruption that lasted 6-7 hours, produced 0.2 km3 of ash and rhyolitic pumice, and created a surge and partially welded ash/pumice fall deposit that crops out on the shore of the modern caldera lake (Sparks et al. 1981). We evaluate the volatile budget of the magma during the eruption and focus on water concentration in glass fragments and shards, glass adjacent to crystals, and melt inclusions (MIs). Sparks et al. (1981) estimated the gas exit velocity at the vent was 380 m/s during the plinian phase, and the water concentration at 2.8 wt%. Measurements of water concentration in basaltic and rhyolitic glass shards from layers C through E range from 0.15 to 0.5 wt%, with variations within layers, a drop in layer D, and increase in layer E. Plagioclase and pyroxene crystals from layers C through E contain rhyolitic MIs with water concentrations ranging from 0.1 to 1.8 wt%, some higher than the matrix glass. Magma underwent degassing on its way to the surface. Rhyolitic glass adjacent to crystals hosting MIs has the highest water concentration, from 0.4 to 2.18 wt%. This, and the initial phreatoplinian eruptive style, both suggest interaction of magma with meteoric water during the eruption. Intimate mixtures of basaltic glass compositions within samples and basaltic glass surrounded by rhyolitic glass support the conclusion of Sigurdsson and Sparks (1981) that magmas mingled prior to and during the eruption.

Styles APA, Harvard, Vancouver, ISO, etc.

45

Lloyd, Alexander. « Timescales of magma ascent during explosive eruptions : Insights from the re-equilibration of magmatic volatiles ». Thesis, 2014. https://doi.org/10.7916/D8F769QW.

Texte intégral

Résumé :

The explosivity of volcanic eruptions is governed in part by the rate at which magma ascends and degasses. Because the timescales of eruptive processes can be exceedingly fast relative to standard geochronometers, magma ascent rate remains difficult to quantify. As an exception to this principle, magmatic volatiles can re-equilibrate on timescales relevant to explosive eruptions, producing evidence for diffusion that can be assessed by various micro-beam techniques. Because the solubility of water and other magmatic volatiles decreases substantially at lower pressures, magmas erupt with a minute fraction of that which was initially dissolved. Melt inclusions, melt embayments, and trace amounts of H2O incorporated into the structure of nominally anhydrous minerals have the potential to retain information about the initial concentrations of magmatic volatiles prior to degassing. In this thesis, I present an assessment of the viability of these hydrous inclusions and mineral phases in preserving initial magmatic conditions in light of post-eruptive cooling effects. In addition, I also present an investigation of the potential of utilizing this volatile loss to estimate time scales of magma ascent during the 1974 sub-plinian eruption of Volcán de Fuego in Guatemala. To test the possibility of systematic H2O re-equilibration in olivine-hosted melt inclusions, I designed a natural experiment using ash, lapilli, and bomb samples that cooled at different rates owing to their different sizes. Ion microprobe, laser ablation-ICPMS, and electron probe analyses show that melt inclusions from ash and lapilli record the highest H2O contents, up to 4.4 wt%. On the other hand, MIs from bombs indicate up to 30% lower H2O contents (loss of ~ 1 wt% H2O) and 10% post-entrapment crystallization of olivine. This evidence is consistent with the longer cooling time available for a bomb-sized clast, up to 10 minutes for a 3-4 cm radius bomb, assuming conductive cooling and the fastest H+ diffusivities measured in olivine (D ~ 10-9 to 10-10 m2/s). On the other hand, several lines of evidence point to some water loss prior to eruption, possibly during magma ascent and degassing in the conduit. The duration of magma ascent that could account for the measured H2O loss was calculated to range from 10 to 30 minutes for the fast mechanism of H+ diffusion and 3.7 to 12.3 hours for the slow mechanism of H+ diffusion. Thus, results point to both slower post-eruptive cooling and slower magma ascent affecting MIs from bombs, leading to H2O loss over the timescale of minutes to hours. Utilizing an established method for assessing magma ascent rates, concentration gradients of volatile species along open melt embayments within olivine crystals were measured for use as a chronometer. Continuous degassing of the external melt during magma ascent results in diffusion of volatile species from embayment interiors to the bubble located at their outlets. The wide range in diffusivity and solubility of these different volatiles provides multiple constraints on ascent timescales over a range of depths. We focused on four 100-200 micron, olivine-hosted embayments which exhibit decreases in H2O, CO2, and S towards the embayment outlet bubble. Compared to the extensive melt inclusion suite also presented in this thesis, the embayments have lost both H2O and CO2 throughout the entire length of the embayment. We fit the profiles with a 1-D numerical diffusion model that allows varying diffusivities and external melt concentration as a function of pressure. Assuming a constant decompression rate from the magma storage region at approximately 220 MPa to the surface, H2O, CO2 and S profiles for all embayments can be fit with a relatively narrow range in decompression rates of 0.3-0.5 MPa/s, equivalent to 11-17 m/s ascent velocity and an 8 to 12 minute duration of magma ascent from ~10 km depth. A two-stage decompression model takes advantage of the different depth ranges over which CO2 and H2O degas, and produces good fits given an initial stage of slow decompression (0.05 - 0.3 MPa/s) at high pressure ( > 145 MPa), with similar decompression rates to the single-stage model for the shallower stage. The magma ascent rates reported here are among the first for explosive basaltic eruptions and demonstrate the potential of the embayment method for quantifying magmatic timescales associated with eruptions of different vigor. I investigated the utility of clinopyroxene as a recorder of the initial water and magma ascent rate using natural phenocrysts erupted during the 1974 eruption of Volcán de Fuego and the 1977 eruption on Seguam Island. The partitioning of water between clinopyroxene and melt was determined by analyzing melt inclusions and the adjacent clinopyroxene host by ion microprobe. For 10 Cpx-hosted MIs from Seguam, the partition coefficient is best predicted by the temperature-dependent parameterization by O'Leary et al. (2010). The diffusivity of H2O in clinopyroxene exhibits a four order of magnitude range in previous experimental studies that prevents a direct interpretation of concentration profiles as a chronometer. To constrain the diffusivity in magmatic phenocrysts, H2O concentration profiles were measured in Cpx from Fuego by ion microprobe and exhibit characteristics that are consistent with diffusive re-equilibration during magma ascent. Using the duration of ascent calculated from the melt inclusions and embayments (10 to 30 minutes), a range of H+ diffusivity was determined that would satisfy these timescales (10-9.20 to 10-10.45 m2/s). The calculated DH+ values are on the same order as the highest diffusivities for H+ in Cpx measured in the laboratory. A comparison of H2O concentrations measured in Cpx from lava and tephra samples from the Seguam eruption demonstrated that Cpx from lava retains less H2O in comparison to the H2O measured in the tephra. Using the DH+ values obtained from the Fuego Cpx, I showed that the difference in H2O between the lava and tephra Cpx can be attributed to post-eruption H2O loss during the estimated ~ 13 minute emplacement of the lava flow. The results from this work indicate that iron-rich clinopyroxene from slowly-cooled basaltic lavas should not be used to reconstruct initial magmatic water contents. The novel findings reported in this thesis are two-fold. Based on evidence from olivine-hosted melt inclusions in volcanic bombs and clinopyroxene in a pahoehoe lava flow, it is unlikely that the initial concentration of water can be preserved if a volcanic product undergoes slow post-eruptive cooling. This fact implies that a portion of the published data on H2O concentrations in olivine-hosted melt inclusions and clinopyroxene may reflect unrecognized H2O loss via diffusion and highlights the importance of reporting the type of volcanic deposit or the clast size from which a sample is extracted. The second novel finding of this thesis concerns the convergence in magma ascent rate estimates from three independent chronometers. In one of the first studies of this magma type, I report relatively fast time scales for magma ascent (~10 minutes from mid-crustal depths) for a basaltic, sub-plinian eruption. Furthermore, the similarity of the estimated timescales from melt inclusions, embayments, and clinopyroxene indicate the validity of any of these chronometers in tracking magma ascent rate. This further expansion of the methods for assessing time scales of volcanic eruptions enables researchers to pursue the complicated relationship between magmatic volatiles, ascent rate, and volcanic explosivity.

Styles APA, Harvard, Vancouver, ISO, etc.

46

Berg, Sylvia E. « Silicic Magma Genesis in Basalt-dominated Oceanic Settings : Examples from Iceland and the Canary Islands ». Doctoral thesis, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-272318.

Texte intégral

Résumé :

The origin of silicic magma in basalt-dominated oceanic settings is fundamental to our understanding of magmatic processes and formation of the earliest continental crust. Particularly significant is magma-crust interaction that can modify the composition of magma and the dynamics of volcanism. This thesis investigates silicic magma genesis on different scales in two ocean island settings. First, volcanic products from a series of voluminous Neogene silicic centres in northeast Iceland are investigated using rock and mineral geochemistry, U-Pb geochronology, and oxygen isotope analysis. Second, interfacial processes of magma-crust interaction are investigated using geochemistry and 3D X-ray computed microtomography on crustal xenoliths from the 2011-12 El Hierro eruption, Canary Islands. The results from northeast Iceland constrain a rapid outburst of silicic magmatism driven by a flare of the Iceland plume and/or by formation of a new rift zone, causing large volume injection of basaltic magma into hydrated basaltic crust. This promoted crustal recycling by partial melting of the hydrothermally altered Icelandic crust, thereby producing mixed-origin silicic melt pockets that reflect the heterogeneous nature of the crustal protolith with respect to oxygen isotopes. In particular, a previously unrecognised high-δ18O end-member on Iceland was documented, which implies potentially complex multi-component assimilation histories for magmas ascending through the Icelandic crust. Common geochemical traits between Icelandic and Hadean zircon populations strengthen the concept of Iceland as an analogue for early Earth, implying that crustal recycling in emergent rifts was pivotal in generating Earth’s earliest continental silicic crust. Crustal xenoliths from the El Hierro 2011-2012 eruption underline the role of partial melting and assimilation of pre-island sedimentary layers in the early shield-building phase of ocean islands. This phenomenon may contribute to the formation of evolved magmas, and importantly, the release of volatiles from the xenoliths may be sufficient to increase the volatile load of the magma and temporarily alter the character and intensity of an eruption. This thesis sheds new light on the generation of silicic magma in basalt-dominated oceanic settings and emphasises the relevance of magma-crust interaction for magma evolution, silicic crust formation, and eruption style from early Earth to present.

Styles APA, Harvard, Vancouver, ISO, etc.

Thèses sur le sujet « Volatile in magmas »

Créez une référence correcte selon les styles APA, MLA, Chicago, Harvard et plusieurs autres