The oceanic lithosphere forms as a residue of partial melting of the mantle beneath the mid-ocean ridge axis. Subduction of this residual layer has a profound impact on the Earth’s thermal and geochemical cycles as the recycling of this layer facilitates heat loss from the Earth’s interior and induces geochemical heterogeneities in the mantle. The goal of this study is to understand the thermal and geochemical evolution of the oceanic lithospheric mantle from a petrological perspective. An empirical geobarometer is calibrated for ocean island xenoliths in order to understand the thermal structure of the oceanic lithospheric mantle. The results of 0.1 MPa experiments from this study and high-pressure experiments from previous studies are used in the calibration. The uncertainties on pressures derived using the above geobarometer are high and hence could not be tested against thermal models for the oceanic lithosphere. The geochemical evolution of the oceanic lithospheric mantle involves post-melting geochemical modifications such as metasomatism. The geochemical evolution of the uppermost oceanic lithospheric mantle is studied using harzburgites from Hess Deep ODP Site 895, which are depleted in moderately incompatible elements relative to the global suite of abyssal peridotites. A comparison between Yb-abundances in Hess Deep harzburgites iii iv and those of a model depleted MORB mantle (DMM) residue reveals that the harzburgites have undergone up to 25% melting, assuming 0.5% melt porosity. Higher light and middle rare earth elements in the Hess Deep harzburgites than the model DMM melting residue are interpreted as the result of plagioclase crystallisation from melts being extracted by diffuse porous flow through the upper mantle. The effect of plagioclase crystallisation does not affect the chemistry of residual mineral phases as evidenced from the depleted light rare earth element abundances in clinopyroxene relative to the bulk rock. Ocean island xenoliths are studied to understand when and where metasomatism occurs in the deeper portion of the oceanic lithosphere. The median values of measured and reconstructed bulk concentration of Al2O3 in most ocean island xenoliths is lower than in abyssal peridotites, which generally would be interpreted as indicating a higher extent of melting in the former. However, a comparison between Yb- abundances in ocean island xenoliths and abyssal peridotites with a model DMM melting residue suggests that the extents of melting in the suites of rocks are broadly similar. Although fewer in number than ocean island xenoliths, abyssal peridotites from several locations have low concentrations of moderately incompatible elements. Metasomatism is observed in both, ocean island xenoliths and abyssal peridotites in the form of higher bulk rock Ce and Nd concentration than the model DMM melting residue but the extent of metasomatism is higher in ocean island xenoliths. There is no correlation between the concentrations of bulk rock Ce, Nd, Sm and Eu of ocean island xenoliths and age of the oceanic lithosphere from which the xenoliths originate. It is interpreted that metasomatism in the lower oceanic lithospheric mantle occurs near the ridge axis above the wings of the melting column. / Graduate / 0996 / 0372

Le domaine allochtone de la chaîne Neoproterozoïque Araçuaí met en jeu de grandes quantités de magma, de la fusion partielle et un gradient thermique élevé, ce que caractérise cette chaîne comme un orogène chaud. La suite tonalitique Galiléia, mise en place dans des métasédiments et déformée à l'état magmatique, représente un énorme batholite qui a fortement influencé le comportement mécanique de la croûte moyenne. L'anisotropie de susceptibilité magnétique (ASM) mesurée à travers le batholite et utilisé comme proxy de la petrofabrique, associé à une étude de la minéralogie magnétique, a permit de définir le comportement paramagnétique de la suite Galiléia et de mettre en évidence une déformation complexe en 3D. Les structures développées dans le magma visqueux résultent d'une combinaison de tectoniques tangentielles induites par la compression, et de forces gravitaires découlant du poids de la croûte sus-jacente. La dynamique du batholite est compatible avec celles déjà décrites pour des roches ductiles d'orogènes chauds. Les datations U/Pb sur zircon et monazites et 40Ar/39Ar sur amphiboles, muscovites et biotites ont permit la caractérisation de l'évolution t hermique du batholite et de contraindre la durée de la déformation. Le batholite Galiléia s'est mis en place à ~580 Ma, au cours d'un important événement magmatique, tectonique et thermique. Les températures sont restées hautes durant les premiers ~50 Ma de l'évolution thermique, favorisant une déformation constante du batholite à l'état magmatique, pendant plusieurs dizaine de millions d'années. De telles hautes températures et une telle déformation stable durant de si longues périodes sont des caractéristiques qui semblent communes au orogènes chaud. Le refroidissement lent estimé à 10°C/Ma après ~500 Ma indique l'exhumation a été très lente, probablement due à l'érosion uniquement. / The allochtonous domain of the Neoproterozoic Araçuaí belt involves large amounts of magma, widespread partial melting, granulitic facies and high geotherm, characterising this belt as a hot orogen. The Galiléia tonalitic suite, emplaced within host metasediments and deformed at magmatic state, represents a huge batholith that strongly influenced the mechanical behaviour of this middle crust. The anisotropy of magnetic susceptibility (AMS) measured through this batholith and used as a petrofabric proxy, combined to a detailed magnetic mineralogy investigation, permitted to characterize the paramagnetic behaviour of the Galiléia suite and therefore to highlight a complex 3D strain deformation. The observed structures developed within the viscous magma resulted from a combination of tangential tectonics induced by the compression, and gravitational forces arising from the load of the overlying crust. The kinematics of the batholith is compatible with that already described for ductile rocks of hot orogens. U/Pb dating on zircons and monazites together with 40Ar/39Ar dating on amphiboles, muscovites and biotites permitted to define the thermal evolution of the Galiléia batholith and its host metasediments and constrain the timing of the deformation. The Galiléia batholith emplaced during an important magmatic, tectonic and thermal event at ~580 Ma. Temperature remained high during the first ~50 Ma of the thermal evolution, promoting a seemingly constant deformation of the batholith at magmatic state during several tens of millions years. Such high temperature conditions and stable deformation kinematics during protracted periods of time are supposed to be characteristic of hot orogen. The slow cooling rate of ~10°C/Ma evidenced after ~500 Ma probably indicate a very slow exhumation probably only conducted by erosion.

A faixa Araçuaí, de idade neoproterozóica, caracteriza-se por apresentar em seu domínio alóctone, uma grande quantidade de intrusões magmáticas, uma crosta parcialmente fundida e rochas de facies granulítica, características de uma geoterma elevada, configurando trata-se de um orógeno quente. A suíte tonalítica Galiléia, alojada em metassedimentos, deformada no estado magmático, representa um grande batólito que influenciou de maneira significativa o comportamento mecânico desta crosta mediana. A Anisotropia de Suscetibilidade Magnética (ASM) medida nesse batólito e usada para um estudo de petrotrama, combinado com uma investigação detalhada sobre a mineralogia magnética, permitiu caracterizar o comportamento paramagnético da Suíte Galiléia e, adicionalmente, trazer informações sobre uma deformacão complexa em 3D. As estruturas observadas se desenvolveram em um magma viscoso resultado de uma combinação da tectônica tangencial induzidas por compressão e forças gravitacionais devido ao peso da crosta sobrejacente. A cinemática do batólito é compatível com aquela descrita para as rochas dúcteis da faixa. Datações U/PB em zircões e monazitas e 40Ar/39Ar em anfibólios, moscovitas e biotitas permitiram definir a evolução termal do batólito Galiléia e de seus metassedimentos hospedeiros e trazer informações sobre o período deformacional. O batólito Galiléia colocouse durante um importante evento magmático, termal e tectônico a ~ 580 Ma. A temperatura permaneceu alta durante os primeiros ~ 50Ma da evolução termal, promovendo uma deformação quase constante do batólito no estado magmático durante várias dezenas de milhões de anos. Tais condições de alta temperatura e cinemática deformacional, estável durante períodos prolongados de tempo, são característicos de orógenos quentes. A taxa de resfriamento vagarosa de ~ 10°C/Ma sugere que após ~500Ma a taxa de exumação foi muito lenta, provavelmente ocasionada apenas pela erosão. / The allochtonous domain of the Neoproterozoic Araçuaí belt involves large amounts of magma, widespread partial melting, granulitic facies and high geotherm, characterising this belt as a hot orogen. The Galiléia tonalitic suite, emplaced within host metasediments and deformed at magmatic state, represents a huge batholith that strongly influenced the mechanical behaviour of this middle crust. The anisotropy of magnetic susceptibility (AMS) measured through this batholith and used as a petrofabric proxy, combined to a detailed magnetic mineralogy investigation, permitted to characterize the paramagnetic behaviour of the Galiléia suite and therefore to highlight a complex 3D strain deformation. The observed structures developed within the viscous magma resulted from a combination of tangential tectonics induced by the compression, and gravitational forces arising from the load of the overlying crust. The kinematics of the batholith is compatible with that already described for ductile rocks of hot orogens. U/Pb dating on zircons and monazites together with 40Ar/39Ar dating on amphiboles, muscovites and biotites permitted to define the thermal evolution of the Galiléia batholith and its host metasediments and constrain the timing of the deformation. The Galiléia batholith emplaced during an important magmatic, tectonic and thermal event at ~580 Ma. Temperature remained high during the first ~50 Ma of the thermal evolution, promoting a seemingly constant deformation of the batholith at magmatic state during several tens of millions years. Such high temperature conditions and stable deformation kinematics during protracted periods of time are supposed to be characteristic of hot orogen. The slow cooling rate of ~10°C/Ma evidenced after ~500 Ma probably indicate a very slow exhumation probably only conducted by erosion.

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

La plate-forme Saharienne paléozoïque, comprenant les bassins péri-Hoggar (Murzuq, Illizi, Mouydir, Ahnet, Reggane et Tim Mersoï) sont définies comme des bassins intracratoniques. Ils ont été dominés par des mouvements verticaux lents et à grande longueur d'onde, conduisant à une subsidence globale à faible vitesse (i.e. ca. 10 m/Ma à 50 m/Ma) et à l'accumulation d'une couverture sédimentaire étendue de type plate-forme (environnements de dépôts peu profonds), rythmée par des périodes pulsatiles d’augmentation et de diminution du taux de subsidence probablement déclenchées par des événements géodynamiques régionaux. Les mouvements verticaux de la plate-forme ont créé plusieurs arches également appelés dômes, paléo-topographies (e.g. les arches de la Tihemboka, d’Amguid El Biod, d’Arak-Foum Belrem et de l’Azzel Matti) et des bassins (en forme de synclinal) de différentes longueurs d'onde allant de plusieurs centaines à plus de milliers kilomètres. La persistance d’un ensemble assez uniforme de mouvements verticaux semble contrôler l’architecture des bassins, ce qui semble indiquer un contrôle à grande échelle (i.e. lithosphérique). Ce dernier contrôle spatialement et temporellement la dynamique sédimentaire de dépôt et d'érosion. Plusieurs périodes d'érosion majeures ont considérablement tronqué les sédiments préexistants sur de vastes zones, produisant des discordances régionales, restreintes et amalgamées sur les arches, qui séparent la couverture sédimentaire de la plateforme. À travers une approche intégrée multidisciplinaire originale allant d’une analyse géologique de bassin, associant le substrat et l’architecture de bassin à une modélisation thermomécanique numérique de la lithosphère, cette étude a permis de décrypter les facteurs de forçage des bassins intracratoniques de la plate-forme saharienne (bassins péri-Hoggar).L'architecture en Arches-Bassins est mise en évidence par l'identification de structures tectono-sédimentaires (onlap divergents, troncatures…). Cette architecture se caractérise par des variations d'épaisseur et des partitionnements de faciès, organisés par des failles normales planes sub-verticales formant des systèmes d'horst-graben souvent associés à des plis forcés dans la couverture. Connectés et nucléés aux grandes zones de méga-cisaillement, les systèmes d'horst-graben sont inversés (inversion positive) ou réactivés (plis forcés) au cours d'événements géodynamiques successifs (par exemple : extension cambro-ordovicienne, rebond glaciaire ordo-silurien, extension/ compression Siluro-Dévonien «Calédonienne», extension/compression du dévonien tardif et compression «hercynienne»).Formée sous une lithosphère précambrienne de type accrétionnaire héritées de plusieurs paléo-orogénèses (e.g. Eburnéenne, Panafricaine), une zonation des substrats sous l’architecture en Arches-Basins est observée : Les terranes Archéen à Paléoprotérozoïque se situent sous les hauts structuraux et les terranes méso-néo-protérozoïques sous les dépressions.Sur la base de ces observations géologiques et de l’hypothèse de densités différentielles conservées (impliquant un potentiel isostatique) entre les différents terranes accrétées héritées (i.e. les terranes archéennes et protérozoïques) dans la lithosphère, un modèle numérique thermo-mécanique 2D est proposé. Les facteurs de forçage du premier et du second ordre, respectivement caractérisés par de faible taux de subsidence et par leurs déviations cycliques pendant de longues durées (250 Ma), sont bien contraint par le modèle réconciliant aussi l’architecture tectono-stratigraphique singulière en Arches-Basins. Les différentes simulations ont montré l’importance des anomalies thermiques, de la tectonique (faible taux de déformation) et de l’apport externes en sédiments sur la dynamique de ces bassins intracratoniques. Le flux sédimentaire contrôle la vitesse et la durée de remplissage du bassin jusqu'à l'équilibre isostatique (…). / The Paleozoic Saharan platform including the peri-Hoggar Basins (i.e. Murzuq, Illizi, Mouydir, Ahnet, Reggane and Tim Mersoï basins) are defined as intracraonic basins. Their histories have been dominated by slow long-wavelength vertical motions leading to overall low subsidence rate (i.e ca. 10 m/Ma to 50 m/Ma) and accumulation of an extensive cover of platformal sediments (i.e. shallow deposits environments), rhythmed by pulsatile periods of increasing and decreasing rate probably triggered by regional geodynamic events. The vertical motions of the platform produced several arches also called domes, swells, highs, ridges (e.g. the Tihemboka, Amguid El Biod, Arak-Foum Belrem and Azzel Matti Arches) and basins (syncline-shaped) with different wavelengths going from several hundred to more than a thousand kilometres. The persistence of a rather uniform pattern of vertical motions seems to control the architecture of the basins indicating a large-scale control (i.e. lithospheric). This latter controls spatially and temporally the deposition and the erosion dynamics. Several major erosion events significantly truncated the pre-existing sediments over wide areas, producing regional unconformities, especially restricted and amalgamated on arches, which separate the platformal cover into divisions. Through an original multidisciplinary integrated approach going from a geological basin analysis, coupling the substrate and the basin architecture to a numerical thermo-mechanical modelling of the lithosphere, this study has led to decipher the forcing factors of the intracratonic basins of the Saharan platform.The Arches-Basins architecture is highlighted through the identification of tectono-sedimentary structures (growth strata, truncatures…). This architecture is featured by thickness variation and facies portioning, organized by sub-vertical planar normal faults (sometimes blind faults) forming horst-graben systems associated with forced folding in the cover. Connected and nucleated to major mega-shear zones, horst-graben systems are inverted (positive inversion) or reactivated (forced folds) during successive geodynamic events (e.g. Cambro-Ordovician extension, Ordo-Silurian glacial rebound, Siluro-Devonian “Caledonian” extension/compression, late Devonian extension/compression and “Hercynian” compression).Formed under a Precambrian lithosphere of accretionary type, inherited during several paleo-orogenies (e.g. Eburnean, Pan-African), a substrates zonation of the Arches-Basins framework is described, where the Archean to Paleoproterozoic terranes are forming the structural highs and the Meso-Neoproterozoic terranes the structural lows.Based on these geological observations and the hypothesis of conserved differential densities (implying an isostatic potential) between the inherited different accreted terranes in the lithosphere (i.e. archean and proterozoic terranes), a 2D thermo-mechanical numerical model is proposed. The first and second order forcing factors, respectively recorded in the subsidence rate pattern by the low long-lived and by their cyclic deviations, are well constrained reconciling the singular Arches-Basins tectono-stratigraphic architecture. The different simulations have shown the importance of thermal anomaly, tectonics (weak strain rate) and external sediment supply on the dynamic of these intracratonic basins. Where, sediment flux controls the speed and the duration of basin infill until achievement of the isostatic equilibrium. The thermal anomaly and the tectonics compel the tectono-stratigraphic complexification such as the arches framework (intra-arches, boundary secondary arches…) and the stratigraphy architecture (wedges, diachronic unconformities) (…).

The upper mantle structure of Swedish part of Baltic Shield with its isotropic and anisotropic seismic velocity characteristics is investigated using telesesismic body waves (i.e. P waves and shear waves) recorded by the Swedish National Seismological Network (SNSN). Nonlinear high-resolution P and SV and SH wave isotropic tomographic inversions reveal velocity perturbations of ± 3 % down to at least 470 km below the network. Separate SV and SV models indicate several consistent major features, many of which are also consistent with P-wave results. A direct cell by cell comparison of SH and SV models reveals velocity differences of up to 4%. Numerical tests show that differences in the two S-wave models can only be partially caused by noise and limited resolution, and some features are attributed to the effect of large scale anisotropy. Shear-wave splitting and P-travel time residual analyses also detect anisotropic mantle structure. Distinct back-azimuth dependence of SKS splitting excludes single-layer anisotropy models with horizontal symmetry axes for the whole region. Joint inversion using both the P and S data reveals 3D self-consistent anisotropic models with well-defined mantle lithospheric domains. These domains of differently oriented anisotropy most probably retain fossil fabric since the domains' origin, supporting the idea of the existence of an early form of plate tectonics during formation of continental cratons already in the Archean. The possible disturbing effects of anisotropy on seismic tomography studies are investigated, and found to be potentially significant. P-wave arrival times were adjusted based on the estimates of mantle anisotropy, and re-inverted. The general pattern of the velocity-perturbation images was similar but changed significantly in some places, including the disappearance of a slab-like structure identified in the inversion with the original data. Thus the analysis demonstrates that anisotropy of quite plausible magnitude can have a significant effect on the tomographic images, and should not be ignored. If, as we believe, our estimates of anisotropy are reasonably correct, then the model based on the adjusted data should give a more robust and correct image of the mantle structure.

The initiation of subduction requires the formation of lithospheric plates which mostly deform at their edges. Shear heating is a possible candidate for producing such localized deformation. In this thesis we employ a 2D model of the mantle with a visco-elasto-plastic rheology and enabled shear heating. We are able to create a shear heating instability both in a constant strain rate and a constant stress boundary condition setup. For the rst case, localized deformation in our specic setup is found for strain rates of 10-15 1/s and mantle temperatures of 1300°C. For constant stress boundaries, the conditions for a setup to localize are more restrictive. Mantle motion is induced by large cold and hot temperature perturbations. Lithospheric stresses scale with the size of these perturbations; maximum stresses are on the order of the yield stress (1 GPa). Adding topography or large inhomogeneities does not result in lithospheric-scale fracture in our model. However, localized deformation does occur for a restricted parameter choice presented in this thesis. The perturbation size has little effect on the occurrence of localization, but large perturbations shorten its onset time.

The surface heat flow (qs) is paramount for modeling the thermal structure of the lithosphere. Changes in the qs over a distinct lithospheric unit are normally directly reflecting changes in the crustal composition and therewith the radiogenic heat budget (e.g., Rudnick et al., 1998; Förster and Förster, 2000; Mareschal and Jaupart, 2004; Perry et al., 2006; Hasterok and Chapman, 2011, and references therein) or, less usual, changes in the mantle heat flow (e.g., Pollack and Chapman, 1977). Knowledge of this physical property is therefore of great interest for both academic research and the energy industry. The present study focuses on the qs of central and southern Israel as part of the Sinai Microplate (SM). Having formed during Oligocene to Miocene rifting and break-up of the African and Arabian plates, the SM is characterized by a young and complex tectonic history. Resulting from the time thermal diffusion needs to pass through the lithosphere, on the order of several tens-of-millions of years (e.g., Fowler, 1990); qs-values of the area reflect conditions of pre-Oligocene times. The thermal structure of the lithosphere beneath the SM in general, and south-central Israel in particular, has remained poorly understood. To address this problem, the two parameters needed for the qs determination were investigated. Temperature measurements were made at ten pre-existing oil and water exploration wells, and the thermal conductivity of 240 drill core and outcrop samples was measured in the lab. The thermal conductivity is the sensitive parameter in this determination. Lab measurements were performed on both, dry and water-saturated samples, which is labor- and time-consuming. Another possibility is the measurement of thermal conductivity in dry state and the conversion to a saturated value by using mean model approaches. The availability of a voluminous and diverse dataset of thermal conductivity values in this study allowed (1) in connection with the temperature gradient to calculate new reliable qs values and to use them to model the thermal pattern of the crust in south-central Israel, prior to young tectonic events, and (2) in connection with comparable datasets, controlling the quality of different mean model approaches for indirect determination of bulk thermal conductivity (BTC) of rocks. The reliability of numerically derived BTC values appears to vary between different mean models, and is also strongly dependent upon sample lithology. Yet, correction algorithms may significantly reduce the mismatch between measured and calculated conductivity values based on the different mean models. Furthermore, the dataset allowed the derivation of lithotype-specific conversion equations to calculate the water-saturated BTC directly from data of dry-measured BTC and porosity (e.g., well log derived porosity) with no use of any mean model and thus provide a suitable tool for fast analysis of large datasets. The results of the study indicate that the qs in the study area is significantly higher than previously assumed. The new presented qs values range between 50 and 62 mW m⁻². A weak trend of decreasing heat flow can be identified from the east to the west (55-50 mW m⁻²), and an increase from the Dead Sea Basin to the south (55-62 mW m⁻²). The observed range can be explained by variation in the composition (heat production) of the upper crust, accompanied by more systematic spatial changes in its thickness. The new qs data then can be used, in conjunction with petrophysical data and information on the structure and composition of the lithosphere, to adjust a model of the pre-Oligocene thermal state of the crust in south-central Israel. The 2-D steady-state temperature model was calculated along an E-W traverse based on the DESIRE seismic profile (Mechie et al., 2009). The model comprises the entire lithosphere down to the lithosphere–asthenosphere boundary (LAB) involving the most recent knowledge of the lithosphere in pre-Oligocene time, i.e., prior to the onset of rifting and plume-related lithospheric thermal perturbations. The adjustment of modeled and measured qs allows conclusions about the pre-Oligocene LAB-depth. After the best fitting the most likely depth is 150 km which is consistent with estimations made in comparable regions of the Arabian Shield. It therefore comprises the first ever modelled pre-Oligocene LAB depth, and provides important clues on the thermal state of lithosphere before rifting. This, in turn, is vital for a better understanding of the (thermo)-dynamic processes associated with lithosphere extension and continental break-up. / Der Oberflächenwärmefluss (qs) ist maßgeblich für die Modellierung der thermischen Struktur der Lithosphäre. Änderungen im qs, innerhalb eines speziellen lithosphärischen Abschnitts, reflektieren direkt Änderungen in der krustalen Zusammensetzung und damit der radiogenen Wärmeproduktion (e.g., Rudnick et al., 1998; Förster und Förster, 2000; Mareschal und Jaupart, 2004; Perry et al., 2006; Hasterok und Chapman, 2011) oder aber, weniger häufig, Änderungen im Mantelwärmefluss (e.g., Pollack und Chapman, 1977). Die Kenntnis dieses physikalischen Parameters ist daher von großem Interesse, sowohl für die Forschung als auch für die Energiewirtschaft. Die vorliegende Studie befasst sich mit dem qs von Süd- und Zentralisrael als Teil der Sinai Mikroplatte (SM), welche während des Riftings und Auseinanderbrechens der Afrikanischen und Arabischen Platte im Oligozän entstand und durch diese, sehr junge und komplexe tektonische Geschichte, geprägt ist. Die thermische Diffusion benötigt einige Zehner-Millionen Jahre (e.g., Fowler, 1990) um die Lithosphäre zu durchlaufen, qs-Werte der Region reflektieren daher prä-oligozäne Bedingungen. Die thermische Struktur der Lithosphäre in Süd- und Zentralisrael, ist bis heute nur sehr wenig verstanden. Um dieses Problem anzugehen wurden die Parameter die für die qs-Bestimmung benötigt werden, eingehend untersucht. An zehn ehemaligen Wasser- und Erdölexplorationsbohrungen wurden neue Temperaturmessungen durchgeführt, und die Wärmeleitfähigkeit von 240 Bohrkern- und Aufschlussproben wurde im Labor gemessen. Die Wärmeleitfähigkeit ist in der qs-Bestimmung der sensitive Parameter. Die Labormessungen wurden sowohl an trockenen sowie an wasser-gesättigten Proben durchgeführt, was personal-und zeitaufwendig ist. Eine andere Möglichkeit ist die Messung der Wärmeleitfähigkeit im trockenen Zustand und das Konvertieren zu einem saturierten Wert unter der Verwendung von Mischungsgesetzen. Das Vorhandensein eines umfangreichen und sehr diversen Wärmeleitfähigkeit-Datensatzes ermöglicht (1) in Verbindung mit dem Temperaturgradienten die Berechnung von neuen zuverlässigen qs-Werten sowie deren Verwendung zur Modellierung der thermischen Struktur der prä-oligozänen Kruste in Israel und (2) in Verbindung mit vergleichbaren Datensätzen, die vorhandenen Mischungsgesetzte zur indirekten Bestimmung der saturierten Gesamtwärmeleitfähigkeit (BTC) qualitativ zu überprüfen. Die Zuverlässigkeit numerisch bestimmter BTC-Werte variiert für die verschiedenen Mischungsgesetze und ist darüber hinaus stark von der Lithologie der Proben abhängig. Mittels spezifischer Korrekturgleichungen können Abweichungen zwischen gemessenen und berechneten Werten jedoch erheblich reduziert werden. Die Datenanzahl und die statistische Analyse ermöglichte darüber hinaus die Ableitung von lithotypspezifischen Konvertierungsgleichungen, um die saturierte BTC anhand von trocken gemessenen BTC- und Porositätswerten (z.B. aus Logs) zu berechnen. Dieser Ansatz führt, für alle Lithotypen, zu einer guten Reproduzierbarkeit gemessener Werte und ist daher eine nützliche Alternative, wann immer große Probenmengen behandelt werden. Die Ergebnisse dieser Studie zeigen, dass der qs im Untersuchungsgebiet signifikant höher ist, als bisher angenommen. Die qs-Werte, die in dieser Studie für Israel bestimmt wurden, schwanken zwischen 50 und 62 mW m⁻². Ein schwacher Trend abnehmender Werte von Ost nach West (55-50 mW m⁻²), und ein leichter Trend ansteigender Werte vom Toten Meer nach Süden (55-62 mW m⁻²) können identifiziert werden. Diese beobachteten Schwankungen lassen sich mit Variationen in der krustalen Zusammensetzung (Wärmeproduktion) erklären, einhergehend mit regionalen Änderungen der Krustenmächtigkeit. Die neuen qs-Daten können dann, im Zusammenhang mit petrophysikalischen Daten und Informationen über die Struktur und Zusammensetzung der Lithosphäre, verwendet werden um ein Model des prä-oligozänen thermischen Zustandes der Kruste Zentral- und Südisraels abzugleichen. Das stationäre 2-D Temperatur-Modell wurde entlang einer E-W Traverse, basierend auf dem seismischen DESIRE-Profil (Mechie et al., 2009), berechnet. Es reicht bis zur Lithosphären–Asthenosphären Grenze (LAB) und bezieht sich auf das aktuellste Wissen über die prä-oligozäne Lithosphäre, also vor dem Einsetzen von Rifting und plumebedingten thermischen Störungen. Durch den Abgleich zwischen gemessenen und modellierten qs-Werten ist es möglich auf die prä-oligozäne LAB-Tiefe zurückzuschließen. Als wahrscheinlichste Tiefe ergeben sich 150 km, was konsistent ist mit LAB-Tiefen Abschätzungen aus vergleichbaren stabilen Regionen des Arabischen Schildes. Dies liefert wichtige Anhaltspunkte über den thermischen Zustand der Lithosphäre vor dem Einsetzen von Rifting in der Region und ist wiederum entscheidend für ein besseres Verständnis der dynamischen Prozesse in Assoziation mit Extension der Lithosphäre und dem kontinentalem Auseinanderbrechen.

Oceanic lithosphere constitutes the upper boundary layer of the Earth’s convecting mantle. Its structure and evolution provide a vital window on the dynamics of the mantle and important clues to how the motions of Earth’s surface plates are coupled to convection in the mantle below. The three-dimensional shear-velocity structure of the upper mantle beneath the Atlantic Ocean is investigated to gain insight into processes that drive formation of oceanic lithosphere. Travel times are measured for approximately 10,000 fundamental-mode Rayleigh waves, in the period range 30-130 seconds, traversing the Atlantic basin. Paths with >30% of their length through continental upper mantle are excluded to maximize sensitivity to the oceanic upper mantle. The lateral distribution of Rayleigh wave phase velocity in the Atlantic upper mantle is explored with two approaches. One, phase velocity is allowed to vary only as a function of seafloor age. Two, a general two-dimensional parameterization is utilized in order to capture perturbations to age-dependent structure. Phase velocity shows a strong dependence on seafloor age, and removing age-dependent velocity from the 2-D maps highlights areas of anomalously low velocity, almost all of which are proximal to locations of hotspot volcanism. Depth-dependent variations in vertically-polarized shear velocity (Vsv) are determined with two sets of 3-D models: a layered model that requires constant VSV in each depth layer, and a splined model that allows VSV to vary continuously with depth. At shallow depths (~75 km) the seismic structure shows the expected dependence on seafloor age. At greater depths (~200 km) high-velocity lithosphere is found only beneath the oldest seafloor; velocity variations beneath younger seafloor may result from temperature or compositional variations within the asthenosphere. The age-dependent phase velocities are used to constrain temperature in the mantle and show that, in contrast to previous results for the Pacific, phase velocities for the Atlantic are not consistent with a half-space cooling model but are best explained by a plate-cooling model with thickness of 75 km and mantle temperature of 1400oC. Comparison with data such as basalt chemistry and seafloor elevation helps to separate thermal and compositional effects on shear velocity.

Le nord-ouest des Alpes est un domaine intraplaque présentant de très faibles déformations. C'est pourquoi il paraît délicat de déduire la probabilité d'occurrence d'un séisme de taille lithosphérique (magnitude supérieure à 7) à partir des observations de microsismicité. De telles observations sont en effet des processus superficiels et présentent peu ou pas de lien avec des processus profonds de plus grande ampleur. L'objectif est de déterminer le potentiel sismique d'un secteur au nord-ouest des Alpes en étudiant le champ de contrainte résultant d'un chargement gravitaire. Seuls les objets de taille lithosphérique, i.e. de l'ordre de la centaine de kilomètres sont pris en compte. Un modèle de contraintes à l'échelle 360 km par 400 km par 230 km d'épaisseur, centré sur la subduction fossile des Alpes de l'ouest et s'étendant jusqu'au nord de Strasbourg, est établi. L'étude des structures du nord-ouest alpin montre l'importance de l'orogène alpin qui se retrouve, enparticulier, dans les variations de profondeur des interfaces de la lithosphère. Une étude du champ de contrainte dans le socle a permis d'identifier une rotation des contraintes principales horizontales avec l'axe des Alpes. Bien que la valeur absolue des contraintes principales n'ait pas pu être déterminée, un rapport de valeur relative est calculé. Le résultat de la modélisation montre l'importance de la rhéologie dans le cas d'un chargement gravitaire. Si une rhéologie élastique est prise en compte, les directions de contrainte calculées sont totalement différentes des observations. Par contre, l'utilisation d'une rhéologie élasto-plastique combinée à l'utilisation d'une géométrie réaliste des interfaces lithosphériques permet d'obtenir des directions de contraintes cohérentes avec les données. / The north-west of the Alps is an intraplate domain with very slow deformations. So, it seems difficult to determine the probability of occurrence of a lithospheric earthquake (magnitude greater than 7) from microseismic observations. Such observations are superficial processes with little relation to deeper and bigger ones. The aim is to determine the seismic potential of a lithospheric sector north-west of the Alps, studying the stress field generated by a gravity driven model. This model is 360 km by 400 km by 230 km deep, centered on the west alpine fossil subduction and going up to the north of Strasbourg. The study of the north-west alpine structures shows the importance of the alpine orogen which generates variations in depth of the lithospheric interfaces. A study of the stress field in the basement shows a variation of principal stress directions along the strike of the Alpine chain. Even if the absolute magnitude of stresses could not be determined a relative magnitude ratio is calculated. Results underline the importance of rheology for a gravity driven model. If an elastic rheology is modeled, calculated stress directions do not match observations. However, using an elasto-plastic rheology with a realistic geometry of the lithospheric interfaces, we can obtain stress directions coherent with the data.