The Okitsu mélange in the Shimanto accretionary complex, the onshore extension of the modern Nankai accretionary prism, consists of a kilometer-size duplex of oceanic basalt and trench-fill sedimentary rocks, and is thought to represent rocks underplated to the prism along the subduction plate-boundary at seismogenic depth. An internal, horsebounding thrust of the duplex, referred to as the Suzume fault, juxtaposes basalt in the hanging wall and sedimentary rocks in the footwall. Structure and fabric of the fault was characterized at the mesoscale to investigate the processes and structural evolution along a plate-boundary décollement. The fault zone in the hanging wall consists of decimeterthick ultracataclasite bounded by a several m thick zone of fractured basalt, and likely records 2+ km displacement along the thrust. The footwall consists of decimeter-thick ultracataclasite bounded by a 20-m-thick zone of ductile shear in flattened sedimentary host rock, and likely records 30+ km of displacement. The asymmetric structure across the Suzume fault, as well as inferred displacement fields and timing relations, are consistent with a tectonic model in which the footwall records early ductile, compactive deformation of poorly consolidated sediments during underthrusting at the prism toe region, followed by extremely localized cataclasis at the underplating depth. In contrast, the hanging wall is deformed by intense cataclasis, and only during underplating. Deformation style and strain state in the footwall of the Suzume fault is qualitatively similar to the modern Costa Rica underthrust section at the toe region. Similarity in the structure and fabric of the hanging wall between the Suzume fault and modern décollement zones sampled through scientific drilling suggests that intense cataclasis under horizontal contraction likely is a common feature for the hanging wall of the décollement zone throughout the toe to underplating regions. Structures in the Suzume fault that are not in common with the modern décollements imply progressive consolidation during underthrusting from the toe to underplating depths may be responsible for the localization of shear in the footwall. At several kilometers depth, displacement along the plate boundary is likely accommodated within an extremely narrow zone as recorded in the ultracataclasite of the Suzume fault.

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Geodetic observations are commonly used to make inferences about the rheology of the lower crust and mantle, frictional properties of faults, and the structure of the Earth following an earthquake. On 24 September 2013, an Mw 7.7 earthquake ruptured a 200 km segment of the Hoshab fault in southern Pakistan. The Hoshab fault is located in the Makran accretionary prism, one of the widest emergent accretionary prisms on Earth. Interferometric synthetic aperture radar (InSAR) time series observations beginning 15 months after the 2013 earthquake capture a large displacement transient in the hanging wall of the Hoshab fault. Using simulations of viscoelastic relaxation and inversions for afterslip along five candidate fault geometries, I find that afterslip alone cannot account for the displacement observed in time series. Instead, I find that the observations can be explained by viscoelastic relaxation of a mechanically weak (viscosity on the order of 1017-1018 Pa s), shallow (>6 km) weak layer within the accretionary prism. First order results indicate this weak layer is between 8-12 km thick with a power law (n=3.5) rheology, and that viscoelastic relaxation is accommodated by dislocation creep at low temperatures. The weak nature of the Makran accretionary wedge may be driven by high pore fluid pressure from hydrocarbon development and underplated sediments.

The Scotland Formation onshore Barbados is often called the only example of a successful hydrocarbon producing accretionary prism reservoir. In spite of this, the hydrocarbon system elements of the BAP have nevertheless not been well studied. Seven outcropping locations of the Scotland were examined to document stacking patterns, key surfaces, depositional element geometries, facies occurrences their vertical and lateral extent, and the unit’s gamma response. Six facies were identified in outcrop: silty muds; laminated, centimeter-scale sandstones interbedded with silts and muds; cross-stratified sandstones; massive, medium to coarse-grained sandstones; very coarse grained sands with gravel or pebbles; and rare conglomerates. These facies combine to form architectural elements—channels, levees, and depositional lobes. Observations from petrographic, outcrop and seismic data suggest that the Scotland Formation was never deeply buried within the prism proper and was possibly deposited within the much larger proto-Tobago Basin. / text

In contrast to the oceans, deformation in the continental lithosphere is distributed over broad regions. This dissertation is composed of three separate but related studies investigating the kinematics and dynamics of such deformation. The first two studies look at the Makran subduction zone, and the third focusses on deformation in South East Tibet. The first study is an investigation of the 11 May 2013 M w 6.1 Minab earthquake which occurred at the western end of the Makran subduction zone, adjacent to the transition to continent-continent collision in the Zagros mountains. Seismological, geodetic and field results are used to study the source parameters and slip distribution of this earthquake, and demonstrate that the earthquake was left-lateral and occurred on a fault striking ENE–WSW; approximately perpendicular to previously studied faults in the adjacent Minab-Zendan-Palami fault zone. Geological and geomorphological observations of similar faults in the vicinity are used to infer that vertical-axis rotations allow a series of such faults to accommodate ∼15–19 mm/yr of N–S right-lateral shear. The dynamic implications for the transition between subduction and continental collision are discussed. The second study looks at the Makran region as a whole. First, the shape and depth of the interface with the Arabian plate is constrained by modelling the depths and mechanisms of earthquakes across the region, and combining these with additional seismological constraints. These constraints on the subduction interface are used to investigate elastic strain accumulation on the megathrust in the western Makran, which has important implications for seismic and tsunami hazard in the region. Second, the kinematics at the northern edge of the Makran accretionary prism are investigated using a combination of geodetic and geomorphological observations, addressing the long-standing tectonic problem of how the right-lateral shear taken up by strike-slip faulting in the Sistan Suture Zone in eastern Iran is accommodated at the zone’s southern end. Finally, the kinematics and dynamics of the accretionary prism are investigated. By considering the kinematics of the 2013 Balochistan and Minab earthquakes, local gravitational and far-field compressive forces in the Makran accretionary prism are inferred to be balanced. This force balance allows the mean shear stress and effective coefficient of friction on the Makran megathrust to be calculated, 5–35 MPa and 0.01–0.03 respectively. The final part of this thesis focusses on the temporal evolution of topography in South East Tibet. Recently published paleoaltimetry results based on stable-isotope geochemistry are used to provide constraints on vertical motions. These demonstrate that uplift is much slower than had previously been suggested from thermochronometric data. Numerical modelling of the time evolution of a gravitationally-driven fluid is used to investigate the effect of lateral rheological contrasts on the shape and evolution of topography. In such a flow, material at the surface can be transported hundreds of kilometres, an effect which should be accounted for in paleoaltimetric analysis. Lateral rheological contrasts, analogous to the relatively undeforming Sichuan Basin and Central Lowlands of Myanmar, can reproduce the main features of the present-day topography, GPS velocity field and earthquake-derived strain rate without the need for a low-viscosity lower-crustal channel.

Les chaînes d'avant pays et les prismes d'accrétion sont des accumulations sédimentaires décollées de la croûte sous-jacente, dans un contexte compressif. En raison de basses températures, la déformation y est frictionnelle et sismogène. Dans la première partie on étudie des échantillons de grès prélevés à proximité de la faille active de Chelungpu, front de déformation du prisme d'accrétion de Taiwan. On montre que l'orientation préférentielle des micro-fractures intra-granulaires existantes ne coïncide pas toujours avec l'orientation des nouvelles micro-fractures produites lors d'essais mécaniques, contredisant des résultats de travaux similaires.La deuxième partie présente l'étude d'une modélisation numérique utilisant l'analyse limite séquentielle d'un prisme frictionnel homogène. On développe cette approche 2D comme une généralisation semi-analytique de la théorie du prisme critique pour suivre la déformation, en intégrant accrétion frontale, adoucissement frictionnel et érosion. Une étude paramétrique systématique révèle le comportement chaotique de la déformation, très sensible aux détails topographiques, mais aussi une organisation statistiquement prévisible des longueurs d'activation du décollement. On distingue par ailleurs une organisation temporelle complexe contrôlée par l'adoucissement frictionnel et les quantités accrétées : par exemple une périodicité d'activation des grandes failles hors-séquence. L'introduction d'une loi d'érosion simple produit un florilège de géométries proches de structures géologiques courantes --- vergence et épaisseur des écailles, duplexes, éventails imbriqués, exhumation. Enfin, une application de la méthode à des expériences de déformation de sables montre la possibilité d'estimer les paramètres de friction in-situ, via des mesures de force. / Chains foreland and accretionary prisms are sedimentary accumulations detached from the underlying crust in a compressive context. Due to low temperatures, deformation is frictional and seismogenic.In the first part we studied sandstone samples collected near the active fault of Chelungpu, deformation front of the Taiwanese accretionary prism. We show that the current preferred orientation of intra-granular microfractures does not always coincide with the orientation of new micro-fractures produced during mechanical testing, contradicting the results of similar work.The second part presents the analysis of numerical modeling using sequential limit analysis of frictional homogeneous prism. We develop this 2D approach as a semi-analytic generalization of the critical prism theory to monitor deformation, including frontal accretion, frictional softening and erosion. A systematic parametric study reveals the chaotic behavior of the deformation --- very sensitive to topographic details --- but also a statistically predictable organization of activation lengths of the décollement. We distinguish also a complex temporal organization controlled by frictional softening and accreted amounts : for example periodicity of activation of large out of sequence faults. The introduction of a simple erosion law produced a plethora of common geological structures --- vergence and thickness of thrusts, duplexes, imbricate fans, exhumation. Finally, an application of the method to sand deformation experiments shows the possibility of estimating in-situ frictional parameters, through force measurements.

En 2004 et 2007, neuf structures d'échappements de fluides (SEF), constituées de volcans de boue (VdB), d'évents de gaz (GS, gas seeps en anglais) et/ou de sources, ont été échantillonnées dans la partie émergée du Bassin de la Côte Est (BCE) de l'île nord de la Nouvelle-Zélande.L'étude granulométrique indique que la boue émise par les VdB, les roches encaissantes et les niveaux de décollement voisins sont composés d'argiles et de silts en majorité. L'étude de la fraction argileuse et de la roche totale par diffraction des rayons X (DRX) a révélé de nombreuses similitudes. Les volcans de boue, les roches encaissantes et les niveaux de décollement présentent ainsi le même assemblage minéralogique, à savoir smectite, illite, chlorite, kaolinite, quartz et feldspaths. Les proportions sont variables d'un échantillon à un autre mais le couple smectite-illite est toujours majoritaire.L'étude géochimique de la fraction solide indique que les échantillons sont riches en Si02, pauvres en Fe2O3, MgO, MnO et en alcalins, à quelques exceptions près. La composition en éléments majeurs s'organise entre un pôle argileux alcalin et un pôle carbonaté. Les spectres de terres rares sont similaires et caractéristiques des argiles ; Ils présentent également un faible degré de fractionnement, lié à la formation des carbonates. Ce sont donc les mêmes minéraux qui contrôlent la chimie des échantillons.L'étude géochimique de la phase liquide montre que l'eau impliquée dans les volcans de boue est d'origine marine essentiellement, et des réactions eau/roche similaires, notamment l'altération de smectite en illite. Cette étude a permis aussi d'obtenir une estimation de la température d'équilibre, comprise entre 60 et 110°C, impliquant une profondeur d'origine de 2 à 3 km, voire plus.L'étude géophysique indique qu'à l'aplomb des VdB et des deux sources chaudes étudiés, la croûte continentale a sensiblement la même épaisseur et que la profondeur de la croûte océanique en subduction avoisine les 20 km. A cette profondeur, la fusion de la péridotite n'est pas possible et la fusion résultante de la croûte continentale, responsable du volcanisme d'arc, non plus. Le gradient géothermique mesuré à TePuia est donc influencé par un autre phénomène, mais la modélisation de la lithosphère ne nous a pas permis de trouver lequel.Ces différentes études mettent en évidence des caractéristiques géochimiques, pétrographiques et minéralogiques communes aux volcans de boue de Nouvelle-Zélande. Les fluides impliqués dans ces structures proviendraient donc d'un même niveau source, recouvert du même assemblage sédimentaire. L'étude géophysique ne nous apporte aucune information à ce sujet mais permet cependant d'établir avec certitude que le régime thermique est le même du Nord de Hawke's Bay au Sud du BCE ; la région de TePuia est un cas particulier, peut-être influencée par le complexe volcanique de Matakaoa. / In 2004 and 2007, nine areas of fluids escapes structures (FES) with mud volcanoes (MVs), gas seeps (GSs) and springs, were sampled in the East Coast Basin (ECB) emerged part of New Zealand's north island.The grain size study indicates that the mud emitted by MVs, like surrounding rocks and decollement layers in the vicinity, is mainly composed of clays and silts. Clay fraction and whole rock XRD study revealed many similarities. Mud volcanoes, surrounding rocks and decollement layers have exactly the same mineral assemblage, i.e. smectite/illite, chlorite, kaolinite, quartz and feldspars. The proportions vary from one sample to another but the couple smectite/illite is always majority.The geochemical study of the solid fraction indicates that the samples are rich in Si02, low in Fe2O3, MgO, MnO and alkaline, with a few exceptions. The major element composition is organized between a pole and a pole clay alkaline carbonate. The REE patterns are similar and characteristics of clays They also have a low degree of fractionation, due to the formation of carbonates. So these are the same minerals that control the chemistry of samples.The liquid phase geochemical study shows that water involved in the MVs is mainly of marine origin, that water/rock reactions are similar, including weathering of illite in smectite, allowed us to obtain an estimate of the water equilibrium temperature between 60 and 110°C, implying an origin depth of 2-3 km.The geophysical study indicates that directly above the MVs and the two hot springs studied, the continental crust has substantially the same thickness and the depth of the subducting oceanic crust is around 20 km. At this depth, the melting of the peridotite is not possible and the resulting fusion of continental crust, responsible of arc volcanism, neither. The geothermal gradient measured at TePuia is influenced by another phenomenon, but the modeling of the lithosphere does not allow us to find which one.These studies show geochemical, petrographical and mineralogical characteristics common to mud volcanoes in New Zealand. Fluids involved in these structures therefore come from the same parent bed, covered with the same sedimentary package. The geophysical study gives us no information about it but nevertheless allows us to establish with certainty that the thermal regime is the same from Northern Hawke's Bay to the south of the ECB; TePuia region is a special case, perhaps influenced by the Matakaoa volcanic complex.

This study shows that remote sensing and GIS are powerful tools in identifying geologically induced lineaments from digitally enhanced ETM+ satellite imageries and the digital elevation model (DEM) in remote areas such as the Makran accretionary prism, southeast Iran. The presence of the conjugate shear fractures in the eastern part, along with the extensional, and the presence of reidal sets associated with the subsidiary fractures of the Minab-Zendal fault system in the western part, suggests that the structural pattern changes from pure shear to simple shear from east to the west across the prism. Moreover, the gradual increase in the value of the angle between the two conjugate shear fractures, from south (coastal Makran) to north across the prism, and the presence of high-angle north-dipping reverse faults, with few south-dipping normal faults, suggest that deformation changes from brittle, in the south, to ductile in the northern part of the prism.

La transition d’un comportement séismique/instable à un comportement aséismique/stable est observée dans la partie en aval des zones sismogéniques (12-15 km de profondeur). Cette transition est supposée être contrôlée par l’activation de la plasticité de basse température du quartz à ~350°C. À cause de la grande profondeur à laquelle cette transition a lieu, le seul moyen pour étudier les processus physiques qui agissent en ces contestés, est l’étude des anciens prismes d’accrétion exhumés actuellement dans des chaines de montagnes. Le mélange tectonique de Hyuga et l’unité de Morotsuka appartiennent au prisme fossile de Shimanto et sont des unités metasédimentaires déformées à des températures peu inférieures ou égales à la limite fragile/ductile (~250 et ~340°C respectivement). Les résultats des observations de microstructures en microscopie optique et en microscopie électronique à balayage (diffraction des électrons rétrodiffusés) confirment que 1) la pression dissolution et une intense microfracturation sont les mécanismes de déformation principaux du quartz dans le mélange de Hyuga et localement l’activation de la plasticité du quartz est aussi observée; 2) dans l’unité de Morotsuka la recristallisation dynamique du quartz est pleinement active. Ces considérations indiquent que la température n’est pas le seul paramètre qui control l’activation de la plasticité du quartz, et laisse supposer la participation de l’effet adoucissant de l’eau. Avec le but de mieux comprendre le rôle de l’eau sur la rhéologie quartz, des expériences en Presse Griggs ont été menées, le matériel du départ étant de porphyroclasts de quartz (immergés dans une matrice sec) à la fois très riches en eau (provenant du mélange tectonique de Hyuga) et secs (quartz du Brésil). Ces expériences montrent l’effet très adoucissant de l’eau, qui à parité de conditions de déformation, favorise la migration de joint des grains dans le quartz de Hyuga tandis que le quartz du Brésil reste indéformé à exceptions de ses bordures extérieures. L’eau « en excès » est expulsée dans la matrice pour le quartz de Hyuga et stockée dans des bandes de cisaillement C’; l’eau incorporée par le quartz de Brésil n’est pas suffisantes pour favoriser la recristallisation dynamique. / The trasition from instable seismic to stable aseismic behaviour is observed in at the lower limit of the seismogenic zones in subduction zones (12-15 km). This transition is supposed to be controlled by the onset of quartz low grade plasticity at about 350°C. Due to inaccessibility of these geodynamic contests, the only way to study the physical processes acting at these depth are exhumed accretionary prisms exposed in mountain chains. The Hyuga tectonic mélange and the Foliated Morotsuka are metasedimentary units constituting the Shimanto accretionary prism (Japan). They were deformed at temperatures of ~250°C and ~340°C respectively, so slightly lower or equal to the temperature transition. Results by optical microscopy and EBSD reveal that 1) quartz deformation mechanisms active in Hyuga Tectonic Mélange are pressure solution and microfracturation accompanied by local quartz low grade plasticity; 2) dynamic recrystallization is totally active in quartz of the Foliated Morotsuka. These considerations allow to consider the role of water in triggering quartz plasticity especially in such water-rich contest as subduction zones. With the aim to better understand the role played by water on quartz rheology, we deformed high hydrated (from Hyuga unit) and dry (classic Brazil) quartz porphyroclasts within a quartz matrix, with the Griggs apparatus. These experiments show the weakening water effect on quartz strength. At the same deformation conditions, the high hydrated Hyuga quartz show recrystallization by grain boundary migration while the dry Brazil porphyroclasts are mostly undeformed, at exception of the outer recrystallized rims. The exceeding water expulsed from Hyuga quartz is stored in C’ shear bands in the matrix; water absorbed by dry Brazil porphyroclasts is not enough to promote dynamic recrystallization.