La croute océanique formée aux dorsales lentes a une composition hétérogène. Pour expliquer sa formation, il est nécessaire d’invoquer des processus d’interactions magma-roche. Afin de contraindre la contribution des processus de cristallisation et d’interaction magma-roche sur le budget géochimique et l’architecture de la croute océanique hétérogène, j’ai étudié deux séquences gabbroiques échantillonnées in situ à l’Atlantis Massif (AM, 30°N, Dorsale Médio-Atlantique, MAR) et l’Atlantis Bank (AB, 57°E, Dorsale Sud-Ouest Indienne, SWIR). J’ai effectué (i) une étude multi-échelle pétro-structurale et géochimique, combinée à une modélisation numérique, de gabbros primitifs forés à l’AM, et (ii) une étude pétrographique et géochimique de gabbros à olivines forés à l’AB. La croute océanique inférieure hétérogène échantillonnée au Site U1309 (AM) présente des troctolites riches en olivines (Ol-T). Elles se distinguent par des olivines partiellement dissoutes, relativement riches en Fo et en Ni, ainsi que par la co-précipitation de clinopyroxènes riches en Mg et de plagioclases. Ces caractéristiques suggèrent que les Ol-T sont le résultat de l’imprégnation d’un protolithe riche en olivines par un magma sous-saturé en olivine. Les profils géochimiques plats entre les minéraux adjacents suggèrent que la composition du protolithe a été modifiée par le magma entrant. Pourtant, le Ni, Li et Co montrent des compositions extrêmement variables à Mg# de l’olivine constant, ce qui suggère qu’ils préservent la signature géochimique du protolithe. La modélisation géochimique indique que ces variations sont héritées d’une hétérogénéité dans les harzburgites U1309. Les expériences en laboratoire ont démontré que la distribution de magma en milieux poreux est contrôlée par la composition modale de la roche percolée. La distribution hétérogène d’orthopyroxène dans le protolithe mantellique contrôle la quantité de magma entrant, et ainsi la quantité d’olivine dissoute, comme indiqué par les variations modales et compositionnelles observées dans les Ol-T à l’AM. La modélisation géochimique indique que la formation des Ol-T peut être expliquée par la percolation de magma et l’assimilation de 5% de protolithe mantellique. Une conséquence de ce processus de réaction est le décalage des compositions du magma à l’AM vers de cristallisation fractionnée apparentes à haute pression. Pourtant, aucune signature géochimique de haute pression n’est observée dans les MORBs à l’AM, alors qu’elles sont observées dans les MORBs d’une portion amagmatique de la SWIR (61°-67°E). La croute océanique à l’AB est faite de gabbros à olivines (75%) et de gabbros à oxides (20%), et par endroits intensément déformée. Les études préliminaires ont mis en évidence des textures indiquant l’assimilation de plagioclase par un magma d’imprégnation, ainsi que la cristallisation de clinopyroxène. Les gabbros à olivines montrent des compositions relativement évoluées. Des études précédentes des gabbros à olivines de l’AB ont montré que leur formation peut être attribuée à l’assimilation de la croute océanique par un magma saturé en clinopyroxène. Les études de l’AM et de l’AB révèlent des processus d’interactions magma-roche associés au transport de magma dans la croute océanique inférieure. Des caractéristiques texturales et géochimiques similaires ont été documentées à Kane (24°N, MAR) et dans les ophiolites Alpines-Apennines. Elles indiquent que les interactions magma-roche sont omniprésentes et contribuent à façonner la croute océanique inférieure aux dorsales lentes. L’étude de roches gabbroiques forées à Hess Deep suggèrent que les interactions magma-roche interviennent également aux dorsales rapides. Le transport réactif de magma dans la croute océanique joue un rôle majeur dans le processus de formation de la croute océanique dans son ensemble. Leur contribution dans la composition des MORBs est probablement contrôlée par la production de magma durant la remontée mantellique. / At slow-spreading mid-ocean ridges the lower oceanic crust is extremely heterogeneous, and its formation must be related to some extents of melt-rock interactions. To constrain the relative contribution of crystallization processes and melt-rock interactions on the geochemical budget and architecture of the slow-spread oceanic crust, I investigated two gabbroic sequences sampled in situ at the Atlantis Massif (AM, 30°N, Mid-Atlantic Ridge, MAR) and the Atlantis Bank (AB, 32°S, 57°E, Southwest Indian Ridge, SWIR), where gabbros are exposed by long-lived detachment faults. I performed (i) a multi-scale petro-structural, geochemical and numerical modeling study of primitive gabbroic rocks drilled at the AM, and (ii) a petrographic and geochemical study of olivine gabbros recovered at the AB. AM was drilled during IODP Expeditions 304/305. The heterogeneous lower oceanic crust recovered at Site U1309 presents discrete intervals of olivine-rich troctolites (Ol-T). They are distinguished by partially dissolved olivines with relatively high Fo (86) and Ni contents (>2000 ppm), and they are characterized by the co-precipitation of high Mg# (86-88) clinopyroxene and plagioclase. These characteristics suggest that Ol-T result from impregnation of an olivine-rich protolith by a melt undersaturated in olivine. The flat geochemical profiles across olivine and adjacent minerals suggest that the composition of the protolith was modified by this impregnating melt. Yet, Ni, Li and Co display extremely variable compositions at constant olivine Mg#, suggesting that they retain the signature of the precursor material. Modeling indicates that these chemical variations are likely inherited from the U1309D harzburgites. Experiments show that the melt distribution and paths in a porous media is controlled by the mineral modes of the host rock. The heterogeneous distribution of orthopyroxene in the precursor harzburgitic mantle locally drives the abundance of impregnating melt, leading to different extents of olivine dissolution, as evidenced by variations in mineral modes and chemistry of the AM Ol-T. Geochemical modeling indicates that the melt percolation and assimilation of about 5% of a mantle protolith can explain the formation of the Ol-T. One consequence of this reactive process in Hole U1309D is the shift of melt compositions toward apparent high pressure fractionation. However, no high pressure chemical signature is observed in MORBs from the AM, while it is recorded in MORBs from the nearly amagmatic region along the SWIR (61°-67°E). AB was drilled during IODP Expedition 360. The recovered lower oceanic crust is dominated by olivine gabbros (75%) and oxide gabbros (20%). The section is in places intensively deformed. Shipboard studies have documented textures of plagioclase assimilation by an invading melt crystallizing clinopyroxene. Compositions of olivine gabbros reach relatively evolved signature (Yb = 3-10 x C1-chondrite; MORB Yb = 19). Previous studies on olivine gabbros from AB showed that their formation can be ascribed to assimilation of an oceanic crust by clinopyroxene-saturated trace element enriched melts. The study of AM and AB reveals melt-rock interactions and mineral assimilation associated to melt transport through the accreting lower oceanic crust. Similar textural and chemical features are observed at Kane (24°N, MAR) and in ophiolite complexes (e.g., Alpine and Appennine ophiolites). These evidences indicate that melt-rock interactions are probably ubiquitous, and contribute to shaping the slow-spread lower oceanic crust. The characterization of gabbroic rocks drilled at Hess Deep suggests that melt-rock interactions may take place also at fast-spreading ridge. Melt transport and associated mineral assimilation processes likely play a major role in the building of the oceanic crust overall. Their contribution to the formation of MORB is likely controlled by melt productivity in the upwelling mantle.

Thesis: Ph. D., Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2018. / Cataloged from PDF version of thesis. / Includes bibliographical references. / This thesis examines abiotic processes controlling the transformation and distribution of carbon compounds in seafloor hydrothermal systems hosted in ultramafic rock. These processes have a direct impact on carbon budgets in the oceanic lithosphere and on the sustenance of microorganisms inhabiting hydrothermal vent ecosystems. Where mantle peridotite interacts with carbon-bearing aqueous fluids in the subseafloor, dissolved inorganic carbon can precipitate as carbonate minerals or undergo reduction by H2(aq) to form reduced carbon species. In Chapters 2 and 3, I conduct laboratory experiments to assess the relative extents of carbonate formation and CO2 reduction during alteration of peridotite by C02(aq)-rich fluids. Results from these experiments reveal that formation of carbonate minerals is favorable on laboratory timescales, even at high H2(aq) concentrations generated by serpentinization reactions. Although CO2(aq) attains rapid metastable equilibrium with formate, formation of thermodynamically stable CH4(aq) is kinetically limited on timescales relevant for active fluid circulation in the subseafloor. It has been proposed that CH4 and potentially longer-chain hydrocarbons may be sourced, instead, from fluid inclusions hosted in plutonic and mantle rocks. Chapter 4 analyzes CH4-rich fluid inclusions in olivine-rich basement rocks from the Von Damm hydrothermal field and the Zambales ophiolite to better understand the origin of abiotic hydrocarbons in ultramaficinfluenced hydrothermal systems. Comparisons of hydrocarbon abundances and stable isotopic compositions in fluid inclusions and associated vent fluids suggest that fluid inclusions may provide a significant contribution of abiotic hydrocarbons to both submarine and continental serpentinization systems. / by Niya Gueorguieva Grozeva. / Ph. D.

De par leurs magnitudes élevées et leur potentiel tsunamigénique, les séismes qui se produisent en contexte de subduction présentent un risque majeur pour les villes côtières souvent densément peuplées. La compréhension de la géométrie et du fonctionnement des zones de failles associées à ces ruptures sismiques a donc fait l'objet de nombreuses recherches sismologiques et géologiques.L’objectif de cette thèse est centré sur la caractérisation des zones de failles paléo-sismiques traversant des formations ophiolitiques subductées puis exhumées en surface des continent et sur leur comparaison avec les zones sismogéniques actuelles. Elle s’appuie sur une approche multi-échelle faisant intervenir les outils de la géologie structurale, de la pétrographie microstructurale, de la minéralogie, de la géochimie ainsi que les données de la géophysique. Le cas de la Corse alpine, de par la présence de nombreuses pseudotachylytes (étant considérées comme des fossiles de séismes) mafiques et ultramafiques constitue un cas d’étude idéal.La rupture sismique dans la nappe du Cima di Gratera est matérialisée par des réseaux de pseudotachylytes parallèles ou à fort pendages situées de part et d’autre de la discontinuité tectonique séparant les unités ultramafiques et mafiques formant la nappe. Le système de faille est caractérisé par une cinématique vers l’ouest associée à la subduction de la plaque océanique liguro-piémontaise sous la plaque adriatique. Les analyses minéralogiques des microlites présentes dans les pseudotachylytes mafiques indiquent une formation des veines en contexte de pression et température du facies eclogite, correspondant à une profondeur comprise entre 60 et 70 km, soit le début de la zone de sismicité dite de profondeur intermédiaire. La géométrie du système de faille a également pu être comparée à des géométries observées via la géophysique au large du nord-est Japon et à des profondeurs similaires.A également été mis en lumière l’impact de la serpentinisation sur le caractère sismique / asismique des discontinuités tectoniques faisant intervenir des formations mafiques et ultramafiques. En effet, la fusion frictionnelle issue des ruptures sismiques et responsable de la formation des veines de pseudotachylytes n’a été observée que dans le cas où était mis en contact la péridotite fraiche ou faiblement serpentinisée et le métagabbro. Les contacts impliquant la serpentinite et le métagabbro n’en présentent jamais et peuvent donc être considérés comme asismiques. Au regard de l’épaisseur des réseaux de pseudotachylytes dans les masses de péridotite et de leur absence dans les serpentinites, les masses de péridotites peuvent donc être assimilées à des aspérités au sein même de la plaque plongeante. / By their high magnitude and their ability to generate tsunami, subduction earthquakes present a major risk for the high population density coastal cities. The understanding of the geometry and the functioning of these seismogenic fault zones was the subject of numerous seismogenic and geologic studies.The objective of this thesis is focus on the characterization of paleo-seismic fault zones cross-cutting subducted ophiolitic formation and exhumed on the continent surface, and their comparison with current seismogenic zones. This study is based on a multi-scale approach and involves structural geology, microstructural petrography, mineralogy, geochemistry and geophysics tools. The Alpine Corsica, by the presence of numerous mafic and ultramafic pseudotachylytes (considered as fossils of past earthquakes) can be considered as an ideal study case.The seismic rupture in the Cima di Gratera Nappe is materialized by pseudotachylyte networks parallel or with a steep dipping to the fault separating the mafic and ultramafic units. The fault system is characterized by a top-to-the-west kinematic associated to the Piemonte-Liguria oceanic plate subduction under the Adriatic plate. The mineralogical analyses of the mafic pseudotachylyte microlites indicate a formation under a pressure and temperature conditions of the eclogite metamorphic facies. These conditions are consistent with a depth between 60 and 70 km which correspond to the upper part of the intermediate-depth seismicity zone. The geometry of the fault system was also compared to some geometry observed by the geophysics in the NE Japan subduction zone and at similar depth.It was also highlighted the role of the serpentinization on the seismic / aseismic character of the fault involving the mafic and ultramafic formations. Indeed, frictional melting resulting from the seismic rupture responsible to the pseudotachylyte veins formation was only observed in the case where the fresh peridotite or weakly serpentinized peridotite is in contact with the metagabbro. By opposition, the deformed zones involving the serpentinite and the metagabbro never show any pseudotachylyte and can be considered as aseismic. Considering the thickness and the polyphaser character of the pseudotachylyte networks and their absence in the serpentinite, the peridotite masses can be considered as asperities within the plate itself.

La présente thèse s'insère dans le projet SALSA (Sergipe Alagoas Seismic Acquisition), mené en collaboration entre le Département de Géosciences Marines; I'IFREMER, I'IUEM, la Faculté des sciences de I'Université de Lisbonne (IDL, Portugal), I'Université de Brasilia (Brésil) et la PETROBRAS (Brésil). Des acquisitions conjointes de sismique réflexion (MCS) et de sismique grand-angle (OBS) ont été réalisées sur le N/O L'Atalante (IFREMER) Ie long de 12 profils sur la région du point triple de Camamú, NE, Brazil. Le point triple de Camamú, où le système de rift avorté Recôncavo-Tucano-Jatobá est relié aux systèmes de rift Jequitinhonha-Camamú-Almada et Jacuípe-Sergipe-Alagoas, a joué un rôle essentiel dans l'ouverture de I'océan Atlantique Sud. Parmi eux, cinq ont été prolongés à terre par des stations sismiques terrestres (LSS). Les modèles de vitesse d'onde P ont été construits sur Ia base de I'interprétation conjointe de données sismiques réflexion et grand-angle en utilisant le logiciel RAYINVR. Nous présentons des modèles de vitesse le long de deux profils parallèles situés dans le bassin de Sergipe-Alagoas (SL01 et SL02), s'étendant sur 220 km et 200 km, respectivement du plateau continental au bassin profond de Sergipe au nord de la zone de transfert de Vaza-Barris. L'un d'eux, le profil SL02 se prolonge sur 150 km à travers le continent, dans la partie continentale du bassin de Sergipe -Alagoas. La modélisation de la marge passive du bassin de Sergipe Alagoas contraint précisément les géométries crustales et la segmentation. Les différences entre les profils éclairent I'influence de I'héritage tectonique résultant de Ia zone de transfert de Vaza-Barris. Ces informations intégrées permettent de nouvelles conjectures autour de I'histoire géodynamique de la région. / The present thesis is inserted in the SALSA project (Seryipe Alagoas Seismic Acquisition), which was conducted by a collaboration between the Department of Marine Geosciences : IFREMER, the Laboratory of Oceanic Domain IUEM, the Faculdade de Ciências da Universidade de Lisboa (IDL, Portugal), the Universidade de Brasilia (Brazil) and PETROBRAS (Brazil).Seismic shot, Multi-Channel Seismic acquisition (MCS) and Ocean Bottom Seismometers (OBS) deployments were performed by the R/V L'Atalante (IFREMER) along 1-2 profiles.Among them, five were extended onshore by Land Seismic Stations (LSS). P-wave velocity models were constructed based on the joint interpretation of multichannel and wide-angle seismic data using the RAYINVR software.We present models derived from wide-angle refraction and coincident reflection data along two parallel profiles located on the Sergipe-Alagoas basin (SL01 and SL02), extending approximately 220 km and 200 km from the continental shelf to the distal Sergipe basin north to the Vaza-Barris Transfer zone, and one of them, the SL02 prolongates for 150 km through the continent, on Sergipe -Alagoas continental basin and its basement, the Sergipana FoId Belt.The foward modelling of the passive margin in the Sergipe Alagoas basin precisely constrains crustal geometries and segmentation. The crustal geometry puts in question the origin of the Sergipana Fold Belt, when compared with the geometries of the adjacent geological domains, the Sao Francisco Craton and the Borborema Province.The differences between the profiles illuminate the influence of the tectonic inheritance resulted by the Vaza-Barris Transfer Zone. These integrated information allowed some new conjectures around the geodynamic history of the region.

Les zones de convergence sont des objets clés à la compréhension de la dynamique de la lithosphère. Elles sont le siège de déformations majeures comme en témoignent la concentration et l’intensité des séismes qui leur sont associées. A plus grande échelle de temps et d'espace, ces déformations résultent généralement en un empilement d’unités dont l’étude offre l'accès aux différents niveaux structuraux mis en jeu dans l'organisation de la chaîne de montagnes. Caractériser précisément la dynamique de structuration de ces unités ainsi que les paramètres contrôlant cette dynamique constitue une étape cruciale permettant d’aller plus loin, notamment quantitativement, dans notre connaissance de la dynamique lithosphérique. Cette thèse a comme double objectif (1) de préciser le comportement rhéologique des roches aux conditions Pressions-Température P-T du faciès éclogitique au sein de l' interface de subduction et (2) de caractériser et quantifier l' influence de la rhéologie de la plaque supérieure, et plus spécifiquement, le rôle de sa partie crustale, sur l'évolution spatio-temporelle des zones de convergence. Pour cela, une approche multi-disciplinaire a été utilisée. Dans un premier temps, je présente une analyse multi-échelle couplant travail de terrain et de pétrologie métamorphique qui a permis d'étudier la déformation au sein de roches HP-BT à l' interface de subduction au niveau de la klippe du Mont-Emilius (Alpes occidentales, Italie). Je détaille ensuite une étude quantitative alliant modélisation numérique thermo-mécanique 3D et 2D de zones de convergence. L'ensemble des modèles a permis d'analyser de nombreux paramètres influençant la structure rhéologique de la plaque supérieure tels que le géotherme initial, l'épaisseur de la lithosphère et de la croûte et la nature des matériaux impliqués. L'ensemble des modèles réalisés sont contraints/confrontés par/aux des données issues d'exemples naturels. Les résultats de l'étude sur des roches déformées au sein de l’interface de subduction mettent en évidence le possible comportement cassant des roches à des conditions de pression et température de l'ordre de 2.15-2.40 GPa, 500-550 °C, i.e., dans le faciès éclogitique. L’enregistrement d’un tel mode de déformation est d'une importance capitale car il remet en question le paradigme d’un comportement ductile sans résistance au niveau de l’ interface de subduction. Les résultats obtenus via les modèles numériques montrent par ailleurs que la rhéologie de la plaque supérieure, ainsi que celle de sa seule partie crustale, a une influence de premier ordre sur la dynamique globale des zones de convergence en modifiant notamment le mode de subduction, la cinématique de la fosse, le mode d'exhumation lors d'une collision, le timing de la déchirure du slab et de la formation de bassins d'arrière-arc, la répartition et l'intensité de la déformation au sein de la plaque supérieure. La combinaison des méthodes de pétrologie et de modélisation numérique a permis d'obtenir une analyse quantifiée de l' influence de la rhéologie des lithosphères impliquées dans les zones de convergence sur la dynamique de ces zones. Cette thèse présente ainsi de nouvelles contraintes à notre compréhension de la réponse mécanique de la lithosphère, en fonction de sa structuration rhéologique et de sa place au sein des zones de convergence à petite et grande échelle. Les nouvelles données présentées révèlent l' impact majeur de la rhéologie de la lithosphère dans les zones de convergence. Ce paramètre amène ainsi à reconsidérer notre vision actuelle des zones de convergence. / Convergence zones are key objects to the understanding of the lithosphere dynamics. They are the location correspond to places of intense deformation as evidenced by the concentration and magnitude of recorded earthquakes. On a larger scale of time and space, these deformations generally result in nappes stacking whose study offers access to the different structural levels involved in the mountain belt structuration. Precisely characterizing the structuring dynamics of these units as well as the parameters controlling this dynamic is a crucial step that would allow in particular a better quantification of lithospheric dynamics. The aim of this thesis is twofold: (1) clarifying the rheological behavior of rocks in the Pressure-Temperature (P-T) conditions of the eclogitic facies at the subduction interface and (2) characterizing and quantifying the influence of the overriding plate rheology, and more specifically, the role of its crustal part, on the spatio-temporal evolution of convergence zones. For this, I used a multi-disciplinary approach. First, I present a multi-scale analysis combining fieldwork and metamorphic petrology, which allowed me to study the deformation within High Pressure-Low Temperature (HP-LT) rocks at the subduction interface in the Mont-Emilius klippe (Western Alps, Italy). Then, I show the results of a quantitative study combining 3D and 2D thermo-mechanical modeling of convergence zones. The entire set of models allowed me to analyze different parameters influencing the rheological structure of the overriding plate, such as the initial geotherm, the thicknesses of the lithosphere and the crust, and the nature of the involved materials. All the performed models are constrained/compared by/with data from natural examples. The results of the study on deformed rocks within the subduction interface highlight the possible brittle behavior of rocks at pressure and temperature conditions on the order of 2.15-2.40 GPa and 500-550 °C, i.e., in the eclogitic facies. The recording of such a deformation mode is of paramount importance because it challenges the paradigm of subduction interface caracterized by ductile behavior without resistance. The results obtained with the numerical models show that the rheology of the overriding plate, as well as that of only its crustal part, has a first-order influence on the overall dynamics of the convergence zones by modifying the mode of subduction, trench kinematics, the mode of exhumation during collision, the timing for slab break-off and back-arc basin formation, the location and intensity of deformation within the overriding plate. The combination of petrology and numerical modeling methods allowed me to obtain a quantified analysis of the influence of the rheology of the lithospheres involved in convergence zones on the dynamics of these zones. This thesis presents new constraints for our understanding of the mechanical response of the lithosphere at different spatial scales as a function of its rheological structure. The new data presented here reveal the major impact of the lithosphere rheology in convergence zones. This parameter leads us to reconsider our current view of the convergence zones.

Les zones de convergence ont des signatures tectoniques, morphologiques et thermiques très variables. Certains orogènes, comme les Andes Centrales, peuvent avoir un régime tectonique localement neutre à extensif, tandis que l'ensemble de la chaîne est en raccourcissement. L'équilibre entre les forces tectoniques et la flottabilité de la croûte détermine la dynamique de la marge. Les paramètres physiques qui contrôlent l'évolution de la marge peuvent être déduits de la topographie ; pour les Andes, les contraintes en jeu varient entre 25 MPa et 75 MPa, la force totale impliquée est d'environ 5.1012 N m-1, la viscosité est de l'ordre de 2.1021 Pa s. Un modèle dynamique de déformation des marges est développé, en assimilant la lithosphère à une plaque mince visqueuse. Des différences mineures dans les conditions aux limites permettent de reproduire convenablement l'évolution de marges actives très différentes, compressives ou extensives. La contribution motrice de la racine lithosphérique à la dynamique est également examinée. Les relations génétiques entre dynamique et régime thermique impliquent une très forte variabilité du champ thermique des marges actives. On distingue les sources de chaleur « statiques » qui incluent le flux de chaleur mantellique et la production radiogénique crustale, et les sources « dynamiques » qui dépendent de la cinématique de l'orogenèse, comme la friction à la base de la lithosphère, le magmatisme, l'ablation convective de la lithosphère, l'érosion, la sédimentation, etc. Une étude théorique systématique permet de hiérarchiser les processus thermiques. Un intérêt particulier est accordé aux perturbations induites par les processus superficiels. Ces investigations sont appliquées aux Andes Centrales, où les données thermiques sont abondantes.

La formation du continent sud américain résulte d'une histoire complexe étalée sur plus de 3.5 Ga. Les processus qui ont façonné le continent ont impliqué l'intégralité de la lithosphère. La structure du manteau supérieur a été étudiée à l'échelle du continent en réalisant un modèle tomographique en ondes de surface, tandis qu'une étude du déphasage des ondes de cisaillement a permis d'appréhender la structure du manteau supérieur sous le sud-est du Brésil.<br /> La tomographie sismique anisotrope en ondes de surface donne une image de la structure en vitesse du manteau supérieur sous le continent et les océans environnants. Une bonne corrélation existe entre les grandes structures géologiques et les hétérogénéités de vitesse. L'anisotropie des ondes de Rayleigh suggère une absence de déformation à grande échelle au-delà de 200 km de profondeur, ce qui contraint verticalement la source de l'anisotropie mise en évidence au sud-est du Brésil. L'étude du déphasage des ondes de cisaillement y a révélé une orientation dominante du plan de polarisation de l'onde quasi-S rapide, parallèle aux chaînes péricratoniques. Un déphasage entre les ondes S rapide et lente supérieur à 2s a été mesuré à l'aplomb des décrochements majeurs. Une telle amplitude suggère que : 1) les décrochements traversent la lithosphère, 2) la lithosphère est caractérisée par une très forte anisotropie intrinsèque, 3) l'asthénosphère contribue au déphasage, par la présence de deux couches ou d'une fabrique tectonique cohérente entre lithosphère et asthénosphère, impliquant une absence de découplage depuis le Néoprotérozoïque.<br /> Une modélisation numérique tridimensionnelle de la déformation lithosphérique a permis d'étudier le couplage mécanique entre la croûte et le manteau supérieur, ainsi que la localisation de la déformation en termes de développement de zones de cisaillement.

Cette thèse a pour but d'évaluer l'hétérogénéité crustale et de comprendre son effet sur la propagation des ondes sismiques. Nous étudions l'énergie de la coda de sismograrnrnes courte période. Pour cela, nous simulons la propagation des ondes en milieu hétérogène en résolvant l'équation de transfert radiatif (ETR) par des méthodes Monte Carlo, La première partie de cette thèse est effectuée dans l'approximation acoustique. Nous résolvons l'ETR dans un milieu composé d'un guide d'ondes hétérogène (la croûte) et d'un demi espace transparent (le manteau). Ces simulations sont comparées aux observations de la coda de séismes régionaux français, Cette étude nous permet de définir un modèle simple pouvant expliquer l'atténuation des ondes Lg directes et de leur coda en temps et en distance. Nous montrons qu 'en France l'atténuation produite par les diffracteurs est de l'ordre de l'absorption anélastique, Dans un deuxième temps, nous étudions la possibilité d'imager un contraste latéral d 'hétérogénéité dans les volcans, Avec des simulations numériques, des analyses de données et des expériences en laboratoire, nous montrons qu'un contraste latéral d'hétérogénéité influence fortement la répartition spatio-temporelle de l'énergie de la coda. La seconde partie est consacrée à la diffusion multiple des ondes élastiques dans un milieu stratifié composé d'un guide d'onde hétérogène d'épaisseur H (croûte) et d'un demi espace homogène (manteau).Une étude de coda-Q montre que la fuite vers le manteau est gouvernée par le libre parcours moyen de transport. L , et cela même si L > > H . Nous montrons également que les valeurs de coda-Q obtenues sont, pour un L donné, identiques à celles mesurées en acoustique. Enfin, nous étudions le phénomène d'équipartition (stabilisation du rapport entre l'énergie des ondes S et P) . Nous montrons que la valeur de stabllisation du rapport dépend de l'anisotropie de scattering et de L.

Made available in DSpace on 2015-02-24T19:48:36Z (GMT). No. of bitstreams: 1 RobertoGO_Capa_ate_pag82.pdf: 4449318 bytes, checksum: a8a67621781bd4f76c4e2c0361bcc6a2 (MD5) Previous issue date: 2008-07-27 / Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico / The Borborema Province (BP) is a geologic domain located in Northeastern Brazil. The BP is limited at the south by the S?o Francisco craton, at the west by the Parna?ba basin, and both at the north and east by coastal sedimentary basins. Nonetheless the BP surface geology is well known, several key aspects of its evolution are still open, notably: i)its tectonic compartmentalization established after the Brasiliano orogenesis, ii) the architecture of its cretaceous continental margin, iii) the elastic properties of its lithosphere, and iv) the causes of magmatism and uplifting which occurred in the Cenozoic. In this thesis, a regional coverage of geophysical data (elevation, gravity, magnetic, geoid height, and surface wave global tomography) were integrated with surface geologic information aiming to attain a better understanding of the above questions. In the Riacho do Pontal belt and in the western sector of the Sergipano belt, the neoproterozoic suture of the collision of the Sul domain of the BP with the Sanfranciscana plate (SFP) is correlated with an expressive dipolar gravity anomaly. The positive lobule of this anomaly is due to the BP lower continental crust uplifting whilst the negative lobule is due to the supracrustal nappes overthrusting the SFP. In the eastern sector of the Sergipano belt, this dipolar gravity anomaly does not exist. However the suture still can be identified at the southern sector of the Maranc? complex arc, alongside of the Porto da Folha shear zone, where the SFP N-S geophysical alignments are truncated. The boundary associated to the collision of the Cear? domain of the BP with the West African craton is also correlated with a dipolar gravity anomaly. The positive lobule of this anomaly coincides with the Sobral-Pedro II shear zone whilst the negative lobule is associated with the Santa Quit?ria magmatic arc. Judging by their geophysical signatures, the major BP internal boundaries are: i)the western sector of the Pernambuco shear zone and the eastern continuation of this shear zone as the Congo shear zone, ii) the Patos shear zone, and iii) the Jaguaribe shear zone and its southwestern continuation as the Tatajuba shear zone. These boundaries divide the BP in five tectonic domains in the geophysical criteria: Sul, Transversal, Rio Grande do Norte, Cear?, and M?dio Corea?. The Sul domain is characterized by geophysical signatures associated with the BP and SFP collision. The fact that Congo shear zone is now proposed as part of the Transversal domain boundary implies an important change in the original definition of this domain. The Rio Grande do Norte domain presents a highly magnetized crust resulted from the superposition of precambrian and phanerozoic events. The Cear? domain is divided by the Senador Pompeu shear zone in two subdomains: the eastern one corresponds to the Or?s-Jaguaribe belt and the western one to the Cear?-Central subdomain. The latter subdomain exhibits a positive ENE-W SW gravity anomaly which was associated to a crustal discontinuity. This discontinuity would have acted as a rampart against to the N-S Brasiliano orogenic nappes. The M?dio Corea? domain also presents a dipolar gravity anomaly. Its positive lobule is due to granulitic rocks whereas the negative one is caused by supracrustal rocks. The boundary between M?dio Corea? and Cear? domains can be traced below the Parna?ba basin sediments by its geophysical signature. The joint analysis of free air anomalies, free air admittances, and effective elastic thickness estimates (Te) revealed that the Brazilian East and Equatorial continental margins have quite different elastic properties. In the first one 10 km < Te < 20 km whereas in the second one Te ? 10 km. The weakness of the Equatorial margin lithosphere was caused by the cenozoic magmatism. The BP continental margin presents segmentations; some of them have inheritance from precambrian structures and domains. The segmentations conform markedly with some sedimentary basin features which are below described from south to north. The limit between Sergipe and Alagoas subbasins coincides with the suture between BP and SFP. Te estimates indicates concordantly that in Sergipe subbasin Te is around 20 km while Alagoas subbasin has Te around 10 km, thus revealing that the lithosphere in the Sergipe subbasin has a greater rigidity than the lithosphere in the Alagoas subbasin. Additionally inside the crust beneath Sergipe subbasin occurs a very dense body (underplating or crustal heritage?) which is not present in the crust beneath Alagoas subbasin. The continental margin of the Pernambuco basin (15 < Te < 25 km) presents a very distinct free air edge effect displaying two anomalies. This fact indicates the existence in the Pernambuco plateau of a relatively thick crust. In the Para?ba basin the free air edge effect is quite uniform, Te ? 15 km, and the lower crust is abnormally dense probably due to its alteration by a magmatic underplating in the Cenozoic. The Potiguar basin segmentation in three parts was corroborated by the Te estimates: in the Potiguar rift Te ? 5 km, in the Aracati platform Te ? 25 km, and in the Touros platform Te ? 10 km. The observed weakness of the lithosphere in the Potiguar rift segment is due to the high heat flux while the relatively high strength of the lithosphere in the Touros platform may be due to the existence of an archaean crust. The Cear? basin, in the region of Munda? and Icara? subbasins, presents a quite uniform free air edge effect and Te ranges from 10 to 15 km. The analysis of the Bouguer admittance revealed that isostasy in BP can be explained with an isostatic model where combined surface and buried loadings are present. The estimated ratio of the buried loading relative to the surface loading is equal to 15. In addition, the lower crust in BP is abnormally dense. These affirmations are particularly adequate to the northern portion of BP where adherence of the observed data to the isostatic model is quite good. Using the same above described isostatic model to calculate the coherence function, it was obtained that a single Te estimate for the entire BP must be lower than 60 km; in addition, the BP north portion has Te around 20 km. Using the conventional elastic flexural model to isostasy, an inversion of crust thickness was performed. It was identified two regions in BP where the crust is thickened: one below the Borborema plateau (associated to an uplifting in the Cenozoic) and the other one in the Cear? domain beneath the Santa Quit?ria magmatic arc (a residue associated to the Brasiliano orogenesis). On the other hand, along the Cariri-Potiguar trend, the crust is thinned due to an aborted rifting in the Cretaceous. Based on the interpretation of free air anomalies, it was inferred the existence of a large magmatism in the oceanic crust surrounding the BP, in contrast with the incipient magmatism in the continent as shown by surface geology. In BP a quite important positive geoid anomaly exists. This anomaly is spatially correlated with the Borborema plateau and the Maca?-Queimadas volcanic lineament. The integrated interpretation of geoid height anomaly data, global shear velocity model, and geologic data allow to propose that and Edge Driven Convection (EDC) may have caused the Cenozoic magmatism. The EDC is an instability that presumably occurs at the boundary between thick stable lithosphere and oceanic thin lithosphere. In the BP lithosphere, the EDC mechanism would have dragged the cold lithospheric mantle into the hot asthenospheric mantle thus causing a positive density contrast that would have generated the main component of the geoid height anomaly. In addition, the compatibility of the gravity data with the isostatic model, where combined surface and buried loadings are present, together with the temporal correlation between the Cenozoic magmatism and the Borborema plateau uplifting allow to propose that this uplifting would have been caused by the buoyancy effect of a crustal root generated by a magmatic underplating in the Cenozoic / A Prov?ncia Borborema (PB) ? um dom?nio geol?gico-estrutural localizado no Nordeste do Brasil, limitado a sul pelo Cr?ton do S?o Francisco, a oeste pela Bacia do Parna?ba e a norte e leste pelas bacias costeiras. Embora bastante estudada por geologia de superf?cie, na PB ainda est?o em aberto aspectos importantes de sua evolu??o, notadamente: i) a sua compartimentagem tect?nica ap?s a Orog?nese Brasiliana, ii) a arquitetura da margem continental implantada no Cret?ceo, iii) as propriedades el?sticas de sua litosfera, e iv) as causas do magmatismo e do soerguimento no Cenoz?ico. Esta Tese empregou dados geof?sicos de cobertura regional (eleva??o, gravimetria, magnetometria, altura geoidal e tomografia), para aportar informa??es de geologia profunda aos problemas acima colocados. A sutura gerada pela colis?o neoproteroz?ica entre o Dom?nio Sul da PB e a Placa Sanfranciscana (PSF) ? marcada, na Faixa Riacho do Pontal e no oeste da Faixa Sergipana, por uma forte anomalia gravim?trica dipolar, cujo pico positivo corresponde ao al?amento da crosta inferior da PB e o negativo corresponde ?s nappes de supracrustais empurradas sobre a PSF. Na regi?o leste da Faixa Sergipana n?o h? assinaturas gravim?tricas que indiquem cavalgamento e flexura de placas, mas a interpreta??o de truncamentos de assinaturas geof?sicas de dire??o N-S da PSF permite localizar a sutura na margem sul do complexo de arco Maranc?, ao longo da Z. C. Porto da Folha. Por sua vez, o limite colisional do Dom?nio Cear? da PB com o Cr?ton Oeste-Africano, ao longo da Z. C. Sobral-Pedro II, ? tamb?m marcado por uma anomalia gravim?trica dipolar, cujo pico positivo coincide com a Z. C. Sobral-Pedro II, e o negativo coincide com o arco magm?tico de Santa Quit?ria. A julgar pela express?o geof?sica, os limites internos mais importantes da PB s?o: i) a Z. C. Pernambuco Oeste e sua continua??o na Z. C. Congo, ii) a Z. C. Patos e iii) a Z. C. Jaguaribe e sua continua??o na Z. C. Tatajuba. Estes limites dividem a PB em cinco grandes dom?nios geof?sicos-tect?nicos: Sul (ou Externo), Transversal, Rio Grande do Norte, Cear? e M?dio Corea?. O Dom?nio Sul ? marcado por assinaturas geof?sicas associadas ? colis?o da PB com a PSF. O Dom?nio Transversal teve a sua concep??o original de limites modificada porque a parte leste do seu limite sul foi associada com a Z. C. Congo. O Dom?nio Rio Grande do Norte apresenta a crosta mais magn?tica da PB, com superposi??o de fontes pr?-cambrianas e faneroz?icas. No Dom?nio Cear?, a Z. C. Senador Pompeu ? o divisor de dois subdom?nios: o leste corresponde ? Faixa Or?s-Jaguaribe e o oeste corresponde ao Cear?-Central, onde ocorre uma assinatura gravim?trica interpretada como uma descontinuidade crustal de dire??o ENE-WSW, que funcionou como um anteparo para as nappes brasilanas, com sentido de deslocamento para sul. O Dom?nio M?dio Corea? apresenta uma anomalia gravim?trica dipolar, cujo pico positivo est? associado com rochas granul?ticas, e o negativo com rochas supracrustais. A assinatura geof?sica do seu limite com o Dom?nio Cear? ? evidente, apesar dos sedimentos da Bacia do Parna?ba. A an?lise conjunta da anomalia ar-livre, admit?ncia ar-livre e estimativas da espessura el?stica efetiva (Te) evidenciou que as margens Leste e Equatorial possuem propriedades el?sticas bastante diferentes: enquanto a primeira tem Te entre 10 e 20 km, a segunda tem Te em torno ou inferior a 10 km. Essa diferen?a ? devida ao enfraquecimento da litosfera da Margem Equatorial produzida pelo magmatismo cenoz?ico. A margem continental da PB apresenta segmenta??es que incorporaram heran?as das estruturas e dos dom?nios pr?-cambrianos, que se correlacionam com os limites conhecidos das bacias. Descrevendo de sul para norte, o limite da separa??o da Bacia Sergipe - Alagoas em duas sub-bacias coincide com a sutura entre o Dom?nio Sul da PB e a PSF; as estimativas de Te indicam, concordantemente, que a Sub-bacia Sergipe (Te ? 20 km) se instalou em uma litosfera mais resistente do que a da Sub-bacia Alagoas (Te ? 10 km). Adicionalmente, no interior da crosta da Sub-bacia Sergipe ocorre um grande corpo denso (underplating ou heran?a crustal?) que n?o continua na Sub-bacia Alagoas. A margem da Bacia de Pernambuco (15 < Te < 25 km) apresenta caracter?sticas diferentes das outras bacias costeiras, porque no Plat? de Pernambuco h? duas anomalias do efeito de borda , o que indica a exist?ncia no plat? de uma crosta continental afinada, contudo ainda relativamente espessa. A Bacia da Para?ba se apresenta bastante uniforme, com Te em torno de 15 km, e possui uma crosta inferior relativamente densa, que foi interpretada como uma modifica??o por underplating magm?tico relacionado com o magmatismo cenoz?ico. A segmenta??o da Bacia Potiguar em tr?s partes ? corroborada pelas estimativas de Te: Rifte Potiguar (Te ? 5 km), Plataforma de Aracati (Te ? 25 km) e Plataforma de Touros (Te ? 10 km). A fragilidade da litosfera na regi?o do Rifte Potiguar est? associada com fluxo t?rmico atual alto, e a resist?ncia relativamente maior da Plataforma de Touros pode ser devida a uma crosta arqueana. A margem da Bacia do Cear?, no trecho das sub-bacias Munda? e Icara?, possui anomalia ar-livre uniforme, com Te entre 10 e 15 km. A an?lise da admit?ncia Bouguer revelou que a condi??o isost?tica da PB ? compat?vel com um modelo em que ocorrem carregamentos combinados na superf?cie e na base da crosta, com a carga da base 15 vezes maior que a do topo. Em adi??o, a PB possui uma crosta inferior anormalmente densa. Estas afirma??es s?o especialmente adequadas para a parte norte da PB porque a? a ader?ncia dos dados observados ao modelo ? maior. Para o mesmo modelo isost?tico e usando a fun??o coer?ncia, estimou-se que a Te da PB deve ser inferior a 60 km, embora sua por??o norte tenha Te de apenas 20 km. A invers?o de espessura de crosta, usando o modelo isost?tico com carga apenas na superf?cie, indicou que existem na PB duas regi?es de espessamento: uma abaixo do Planalto da Borborema (de origem cenoz?ica) e a outra no Dom?nio Cear?, sob o arco magm?tico de Santa Quit?ria (vestigial do Pr?-cambriano). Por outro lado, ocorre um afinamento ao longo do Trend Cariri-Potiguar, que representa o registro no interior do continente de um rifteamento cret?ceo abortado. A interpreta??o das anomalias ar-livre de fontes oce?nicas levou ? proposi??o de que ocorreu um volumoso magmatismo na ?rea oce?nica adjacente ? PB, ao contr?rio da ?rea continental, como indicam as informa??es de geologia de superf?cie. A PB apresenta uma expressiva anomalia positiva de ge?ide, com correla??o espacial com o Planalto da Borborema e o Alinhamento Macau-Queimadas. A integra??o de dados de tomografia de ondas superficiais e de anomalias residuais de ge?ide permitiu interpretar que uma convec??o em pequena escala (Edge Driven Convection-EDC), gerada na interface entre a raiz da litosfera continental fria e o manto quente da ?rea oce?nica, pode ter sido a causa do magmatismo cenoz?ico. O mecanismo de EDC teria causado o arrasto do manto litosf?rico continental frio para dentro do manto astenosf?rico quente, ocasionando assim contraste positivo de densidade, que seria uma componente importante da origem da anomalia de ge?ide. A compatibilidade dos dados gravim?tricos da PB com o modelo isost?tico que combina carregamentos no topo e na base da crosta, e a correla??o temporal entre o magmatismo cenoz?ico e o soerguimento do planalto, permite propor que o soerguimento deste ocorreu por causa do empuxo provocado pela raiz da crosta, produzida por um underplating magm?tico no Cenoz?ico

Orientador: Maurício Compiani / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Geociências / Made available in DSpace on 2018-08-19T00:25:03Z (GMT). No. of bitstreams: 1 Garcia_FabianaBurgosTakahashi_M.pdf: 5270236 bytes, checksum: 1fa1e53fc6bf45eb1dcc6fa74e637d09 (MD5) Previous issue date: 2011 / Resumo: A presente dissertação tem seu olhar voltado para o currículo da disciplina escolar química e sua relação com as geociências. Este trabalho foi desenvolvido no contexto do projeto apoiado pela Fundação de Amparo à Pesquisa de São Paulo (FAPESP) - Ensino Público intitulado "Elaboração de conhecimentos escolares e curriculares relacionados à ciência, à sociedade e ao ambiente na escola básica com ênfase na regionalização a partir dos resultados de projeto de Políticas Públicas", cujo recorte de análise era a bacia do Ribeirão das Anhumas, onde está inserida a escola estadual que foi cenário principal desta dissertação e onde atuavam professores, alunos e acadêmicos. Baseando metodologicamente na perspectiva da pesquisa-ação sugerida por Mckernan principalmente, foi possível sistematizar este trabalho de modo que a importância do professor na elaboração do currículo fosse evidenciada, como propõe o mesmo autor. Neste sentido, a pesquisadora, professora da escola básica, voltou-se para seus instrumentos de trabalho questionando-os e sugerindo alterações. Então foi realizada uma revisão dos documentos oficiais que contribuíram para a elaboração da Proposta Curricular do Estado de São Paulo para o Ensino de Química (PCEQ) sob o olhar da contextualização e interdisciplinaridade visando mostrar que as discussões acerca da elaboração de currículos com esta conotação não são recentes. Além disso, os cadernos do professor e do aluno que complementam a PCEQ, e o livro didático utilizado em sala pela pesquisadora também foram analisados abordando a presença ou não do tema "Química e Litosfera" bem como o tratamento dado a esta temática quando presente no material, uma vez que é sugerido nas Orientações Complementares aos Parâmetros Curriculares Nacionais (PCN+), porém ausente na PCEQ. Por isso que em meio a discussões e reflexões colaborativas do subgrupo Ensino-Aprendizagem, nas quais a interdisciplinaridade era discutida e utilizada como referencial para elaborar e desenvolver atividades escolares dentro do contexto local, e também com base nas lacunas encontradas durante estas análises, é que foi possível complementar o referido material. Dentre todas as atividades, podemos dizer que o trabalho de campo foi talvez o mais importante, afinal, foi possível perceber que os alunos tinham conhecimento para explicar a formação dos solos a partir das interações que ocorrem no ambiente, partindo de observações da paisagem local. Desta forma, pudemos nos aproximar dos objetivos de incorporar ao currículo de química o tema citado utilizando conhecimentos sobre a Bacia do Ribeirão das Anhumas, local onde a escola se insere. Enfim, a inserção do tema faltante na PCEQ vem suprir necessidades de conteúdos, enquanto promove junto com a abordagem local a superação de problemas reais e escolares, e tudo isso dentro de uma dinâmica de colaboração entre os atores envolvidos naquele cenário / Abstract: This dissertation focuses the curriculum of the Chemistry discipline and its relation with the Geosciences. This paper was developed in the context of the FAPESP Public Teaching Project entitled "Construction of school and curricular knowledge relative to science, society and environment at primary and secondary school with emphasis in the local conditions from results of public politicians projects" which focused its analysis in the basin of the Brook of Anhumas where the state school is located. This school was the scenario of this research whose professors, teachers and students maintained a collaboration relationship and learning to the development of this study. Using Mckerman methodological approach of action-research, it became possible to design a system of work with a view to emphasize the importance of the teacher in the elaboration of the curricular content, as the author proposes. Therefore, the researcher who is also a teacher at the secondary school, looked at her working tools, questioned them and suggested changes. Official documents that contributed to the elaboration of PCEQ were also reviewed in the light of context and interdisciplinary relations with a view to show that discussions about curricular contents using this concept are not new. Teacher's and student's notebooks which complement the PCEQ and the didactic book used by the researcher were also analyzed to ascertain whether or not they contained the theme "Chemistry and the Lithosphere" as well as how the subject is mentioned in the books, since its use is suggested in the PCN+ but is, however, absent from the PCEQ. Based on the collaborative discussions of the sub-group "Teaching-Learning", where the subject of interdisciplinarity was discussed and used as reference to elaborate and develop school activities within the local context, and also using the gaps found during these analyses it was possible to develop complementary material. Amongst all the activities we can say that the field work was perhaps the most important, as it made possible to perceive that the students had acquired the knowledge to explain the soil formation from the interactions that occur in the environment using as the starting point for their comments the local landscape. Therefore we could reach our goal of incorporating to the Chemistry curricular studies the subject above mentioned using the data of the basin of Brook of Anhumas where the school is located. At last the insertion of the missing subject in the PCEQ comes to suffice necessities of contents while it makes possible to overcome, with a localized approach, existing school problems promoting a collaborative dynamics among all the participants involved in that particular scenario / Mestrado / Ensino e Historia de Ciencias da Terra / Mestre em Ensino e Historia de Ciencias da Terra