Subduction of an oceanic plate under the Pacific margin of South America has heen prevalent since Jurassic times. Magmatic and deformation centres have migrated eastward since suhduction began. Northern Chile houses two north-south trench linked strike-slip fault systems, the Atacama Fault Zone and the Domeyko Fault System (DFS). The DFS lies within the Chilean Precordillera from 2 10 to 28°S. Lateral movement began on the DFS in the Eocene. The DFS can be divided into three segments which have apparently undergone differing deformation histories. This study has focused on the central segment of the DFS, to determine fault kinematics and to establish a relative chronology of deformation. Observations have been made in more detail than previous investigations and have heen used to infer the deformation history . Shallow level faulting has resulted in heavily fractured zones with occasional slickenline surfaces. It is difficult to infer kinematics of faulting from these. Much effort has been expended in developing techniques to analyse fracture patterns associated with brittle faulting under conditions of plane strain, simple shear. A novel approach of analysing the shapes of clasts of rock defined by secondary fractures within a fault zone has been used. The clasts approximate ellipses when viewed in 2 dimensions. Combining ellipse orientation and aspect ratio from mutually perpendicular sections through the fault zone allowed calculation of an ellipsoid representative of the clasts of rock in 3 dimensions. Independent determination of the fault kinematics using stratigraphic relationships across the fault, fracture distribution, incremental strain axes and palaeomagnetic analysis has all owed evaluation of the new technique. The shapes of rock clasts are found to be related to the kinematics of the fault system. Up to a critical stage of development of the fault zone the axes of the rock clasts parallel the slip direction, intermediate strain axis and pole to the boundary faults. Which rock clast axis parallels which structural feature depends upon the spacing and curvature of fractures and stage of development of the fault zone. Analysis of the shapcs or rock clasts defined by fractures can avoid bias of the data set towards thicker fractures or against irregular fractures, which can occur when measuring fracture orientations directly. The degree of development of the fault zone varies laterally along the fault over short distances. This causes the shape.: fabric of the rock clasts to change, so predictions of connectivity within a fault zone are limited. The history of the central segment of the DFS determined from this study is found to occur with earlier workers. The complementary deformation histories produced from two scales of ohservation verifies the reliability of the chronology. Lateral movements along the DFS are thought to begin in the Eocene with a sinistral transpressive event which occurred along all three segments of the DFS. En echelon folds, east and west verging thrusts and clockwise rotations associated with sinistral faulting along the master fault of the segment are documented. Later, in the Oligocene, dextral faulting occurred. large clockwise palaeomagnetic rotations, determined from Palaeozoic samples beside the master fault, indicate sinistral displacements have been larger than dextral disp acements. It is inferred that only one episode of large lateral transport occurred. This is the Eocene sinistral event. Normal faulting associated with sinistral displ acements along the western side of the system are documented. This later sinistral faulting has not been documented before in the central segment of the DFS. After Oligocene age dextral faulting, the three segments of the DFS underwent separate deformation histories, as the main Andean deformation foci had moved eastward.

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The southern Patagonian Andes record the Late Cretaceous closure and inversion of the Late Jurassic – Early Cretaceous Rocas Verdes marginal basin, subsequent development of the Patagonian retroarc fold-thrust belt and the Neogene to present tectonic superposition of a left-lateral strike-slip plate margin defined by the Magallanes- Fagnano fault zone. In this dissertation, I present new geologic maps, cross sections and detailed macro- and microscopic structural analyses that describe the geometry and kinematic evolution of the fold-thrust belt and superposed strike-slip deformation over ~200 km along-strike between 53° and 55° S latitude. Results are discussed in the context of the regional tectonic development of the southernmost Andes and are relevant to the understanding of important tectonic processes including the development of a retroarc fold-thrust belt, the formation of a basal décollement below and toward the hinterland of a fold-thrust belt and the spatial distribution of deformation along a strike-slip plate margin. New maps and balanced cross-sections of the Patagonian fold-thrust belt show that it developed during two main phases of Late Cretaceous to Paleogene shortening that were partly controlled by the antecedent geology and mechanical stratigraphy of the Rocas Verdes basin. During the Late Cretaceous, a thin-skinned thrust belt developed above a décollement that formed first in relatively weak shale deposits of the Rocas Verdes basin and later deepened to <1 km below the basement-cover contact. Ramps that cut mechanically rigid volcanic rocks of the marginal basin link the two décollements. Basement-involved reverse faults that cut the early décollements and probably reactivate Jurassic normal faults reflect Paleogene shortening. Shortening estimates increase northwest to southeast from 26 to 37% over 100 km along-strike and are consistent with regional models of the fold-thrust belt. Structural data, kinematic analyses, and microstructural observations from the lower décollement show that it is defined by transposition of several generations of northeast-vergent noncylindrical folds, shear bands, and a quartz stretching lineation that are kinematically compatible with first-generation structures of the fold-thrust belt. Quartz microstructural data from the décollement are consistent with deformation temperatures that decrease from ~500-650° C to ~400-550° C over ~75 km in the transport direction, indicating that the décollement dipped shallowly (~6°) toward the hinterland. The décollement decoupled the underthrust continental margin from the fold- thrust belt and exemplifies the kinematic relationship between shortening that occurs coevally in a retroarc fold thrust-belt and its polydeformed metamorphic ‘basement’. Fault kinematic data and crosscutting relationships show kinematic and temporal relationships between populations of thrust, strike-slip and normal faults that occur in the study area. Thrust faults form an internally compatible population that shows subhorizontal northeast-trending shortening of the fold-thrust belt and is kinematically distinct from populations of normal and strike-slip faults. Both strike-slip and normal faults crosscut the fold-thrust belt, are localized near segments of the Magallanes- Fagnano fault zone, have mutually compatible kinematic axes and are interpreted to be coeval. Strike-slip faults form Riedel and P-shear geometries that are compatible with left-lateral slip on the Magallanes-Fagnano fault-zone. Strike-slip and normal faults occur in a releasing step-over between two overlapping left-lateral, left-stepping segments of the Magallanes fault zone and record a tectonic event defined by sinistral transtension that probably reflects changing plate dynamics associated with the opening of the Drake Passage during the Early Miocene. / text

Le but de cette étude est de caractériser par une approche multi-disciplinaire les déformations tectoniques Plio-Quaternaire associées au système de failles de Belledonne (Alpes de l'Ouest).Ce système de faille est composé de plusieurs décrochements qui sont des Bauges au Vercors, la faille dextre NE-SW de l'Arcalod, la faille bordière de Belledonne, dextre et NE-SW, la faille sénestre NW-SE du Brion et la faille NE-SW dextre du Jasneuf.La détermination des états de contraintes tardi-Cénozoique montre que le champ de contrainte actuel responsable de la cinématique en décrochement le long du système de faille de Belledonne date de la fin du Pliocène supérieur/début du Pléistocène et a succédé au champ de contrainte causé par la collision alpine.Les failles de l'Arcalod et du Brion présentent des marqueurs morphologiques décalés mais ambiguës et d'âge incertain (probablement anté-Rissiens). La trace de la faille bordière de Belledonne n'a pu être déterminée, suggérant que la déformation associée à cette dernière soit accommodée dans une large bande de cisaillement.La faille du Jasneuf décale des morphologies d'âges supposés messiniens et anté-Rissiens. La vitesse de cette faille intégrée depuis le messinien serait de 0,13±0,03 mm/an. Considérant que cette faille est limitée à la couverture elle pourrait générer des séismes de magnitude 5,7 tous les ~500 ans.L’accommodation de la déformation actuelle dans l'avant-pays a été étudié dans la vallée de Toulaud (SW de Valence) où une faille tardi-hercynienne recoupe le canyon messinien du Rhône. Les premiers résultats indiquent que la faille décale verticalement le canyon, attestant d'une tectonique Plio-Quaternaire. / The aim of this study is to characterize the Plio-Quaternary tectonic deformations related to the Belledonne fault system (western Alps). The low deformation rates and high erosion rates in the study area imply that a multi-disciplinary approach.From the Bauges to the Vercors massif this fault system is composed of strike-slip faults that are the NE trending right-lateral strike-slip Arcalod fault, the NE trending right-lateral strike-slip Belledonne border fault, the NW trending left-lateral strike-slip Brion fault and the NE trending right-lateral strike-slip Jasneuf fault.The determination of the late Cenozoic stress states revealed that the modern stress field responsible for the Belledonne fault system strike-slip kinematics dates from late upper Pliocene/early Pleistocene and came after the stress field caused by alpine collision.Unclear and undated (but probably pre Rissian) offset morphologic markers are described along the Arcalod and Brion faults. Belledonne border fault trace is not determined suggesting that deformation is accommodated in a wide shearing band.The Jasneuf fault offset morphologies whom ages are supposed Messinian and pre Rissian. Fault slip rate integrated since Messinian would be of 0.13±0.03 mm/yr. Considering that this fault appears limited to the sedimentary cover and excluding an aseismic behavior, she can generate 5.7 Mw earthquake each ~500 years.Modern deformation in the foreland is studied in the Toulaud valley (SW of Valence city) where a late Hercinian fault cross-cut the Messinian canyon of the Rhône river. First results show that the fault offset vertically the canyon, attesting aof Plio-Quaternary tectonics along it.