La chaîne hercynienne construite à la fin du Paléozoïque résulte de la convergence entre deux plaques majeures Laurussia et Gondwana. L'objectif de ce travail est d'étudier le potentiel des bassins sédimentaires à enregistrer la naissance des reliefs et l'exhumation des roches au cours des stades précoces de cette orogène. Les séries sédimentaires étudiées (Ordovicien à Carbonifère de l'Unité des Mauges, Domaine-Sud Armoricain, France), bien que localisées dans les zones internes de la chaîne, sont faiblement déformées. Une approche pluridisciplinaire (structurale, sédimentologique, géochronologique) a été développée pour contraindre la paléogéographie de la chaîne et la nature du matériel en cours d'érosion durant sa construction. Les séries sédimentaires ordoviciennes à dévoniennes enregistrent un rifting Dévonien inférieur marqué par une discordance (formation d'épaulements de rift). Cet évènement pourrait être lié à l'ouverture d'un bassin arrière-arc (St-Georges-sur-Loire). L'existence de l'arc magmatique est enregistrée par des zircons détritiques à ca. 400 Ma dans la Fm de Sainte-Anne. La lacune de sédimentation du Dévonien moyen pourrait être liée à une période d'émersion. Le retour de la mer après une destruction des premiers reliefs a lieu au Dévonien supérieur. La collision intervient à la transition Dévonien/Carbonifère. Les séries carbonifères (Fm d'Ancenis) sont préservées dans un bassin grâce à une réactivation de la zone de suture du bassin arrière-arc. La méga-séquence régressive identifiée enregistre une surrection des reliefs et l'exhumation progressive du matériel hercynien (roches magmatiques et métamorphiques).

La thèse porte sur les mécanismes de déformation des couvertures sédimentaires des massifs cristallins de Belledonne, Grandes Rousses et Pelvoux. Elle consiste en une analyse des marqueurs de la déformation : plis, schistosité, fractures, failles et fossiles déformés qui permet d'évaluer les valeurs de la déformation finie dans l'objectif de mieux comprendre la cinématique des déformations alpines. Celle-ci se décline en une succession d'épisodes de déformation dans un contexte de chevauchement des massifs, influencé par le bâti structural préexistant. Une étude des inclusions fluides des cristaux de colmatage des fractures a permis également d'obtenir des informations sur l'évolution des conditions thermodynamiques de cette déformation à travers la croûte supérieure.

This thesis presents elastic finite difference simulations of two dimensional wavefield propagation for line-9, recorded during the 1993 part of the multi-institutional, multi-year Mendocino Triple Junction (MTJ) Seismic Experiment. Line-9 is a high-resolution, large-aperture seismic profile oriented in north-south direction, extending from the subduction regime north of the MTJ to the transform regime south of the MTJ. Snapshots of the wavefield are recorded during the simulation to create a movie which assists with the analysis of the synthetic seismograms. The simulations are computed on a 64 processor CM-5 parallel supercomputer. First a velocity model obtained by the Mendocino Working Group is examined. The model is based on information from depth-migrated single-fold reflection profiles and tomographic inversion of first arrivals. The synthetic seismic sections show acceptable first arrival traveltime fit but fail to correctly model secondary arrivals and amplitude variations of the wavefield. Based on the shortcomings of the initial model an alternative model for the north-south line is proposed. The new model introduces several distinct structures, like a subducted Gorda plate, a slabless window, and a wedge shaped low velocity zone between Franciscan material and Gorda plate. The big difference between the two models is that the initial model is too smooth to contain any discontinuities and cannot account for any reflection arrivals. In addition all structures in the lower crust of the alternative models are located about 4 km deeper than the equivalent velocities in the initial model. The seismic sections of the alternative model show much improved traveltime and amplitude fit. Also, some characteristics of the wavefield observed in the field data (e.g. traveltime oscillations, amplitude variations, and discontinuous arrivals) are also observed in the synthetic seismograms.. The position of the southern end of the Gorda plate (SEDGE) is at 80 km in the model (39.7°N). Because of the limited resolution it is not possible to resolve whether the Gorda plate just north of the SEDGE is fragmented or continuous. To add attenuation by scattering or coda waves generation to the model, the effects of a stochastic velocity description for Franciscan rocks on the wavefield are explored. The best velocity contrast between sandstones and melange units in a bimodal, seifaffine, sinuous connected model is determined as 0.5 km/s. Stochastic models of this kind successfully model background noise and coda waves and to some degree discontinuous phases, amplitude variations, and traveltime oscillations. They cannot, however, account for the full range of characteristics observed in the field data. For this, additional large scale velocity variations must be added to the model. For the final model, the (deterministic) alternative model and the statistical description of Franciscan rocks are combined. The resulting wavefield shows good amplitude and traveltime fit and the observed wavefield characteristics are similar to the characteristics of the field data. / Graduation date: 1997 / Best scan available for figures.

Two examples of Pacific rim plate boundary deformation are presented. In the first part of the thesis crustal models are derived for the northwestern part of the Vizcaino block in California using marine seismic and gravity data collected by the Mendocino Triple Junction Seismic Experiment. A northwest-southeast trending kink in the Moho is imaged and interpreted to have formed under compression by reactivation of preexisting thrust faults in the paleoaccretionary prism at the seaward margin of the Vizcaino block. The study suggests that the deformation resulted from mainly north-south compression between the Pacific-Juan de Fuca plates across the Mendocino transform fault and predates late Pliocene Pacific-North America plate convergence. In the second part, 195 earthquakes recorded during the duration of the Southern Alps Passive Seismic Experiment (SAPSE) are analysed. Precise earthquake locations and focal mechanisms provide unprecedented detail of the seismotectonics in the central South Island. The short term (6 month) SAPSE seismicity is compared with long term (8 years) seismicity recorded by the New Zealand National Seismic network and the Lake Pukaki network. The seismicity rate of the Alpine fault is low, but comparable to locked sections of the San Andreas fault, with large earthquakes expected. Changes of the depth of the seismogenic zone, generally uniform at about 10-12 km, occur only localised over distances smaller than 30 km, suggesting that thermal perturbations must be of similar scale. This implies that the thermal effects of the uplift of the Southern Alps do not change the seismogenic depth significantly and are not in accordance with most of the present thermal models. Both the Hope and Porters Pass fault zones are seismically active and deformation is accommodated near the fault zones and in the adjacent crust. North of Mt Cook, a triangular shaped region along the Alpine fault is characterised by absence of earthquakes. We interpret this as the result of the plate boundary shift from the Alpine fault to the Hope and Porters Pass fault zones. The study region shows distributed deformation in a 60-100 km wide zone on NNE-SSW trending thrust faults and strike-slip mechanisms on transfer faults. / Graduation date: 2000 / Best scan available for black and white figures.

The anisotropy of magnetic susceptibility (AMS) was investigated in three Chinese Loess Plateau sedimentary sections along a W–E transect. Previously published models assumed that winter monsoons were responsible for the magnetic fabric formation of loess sequences. In our new interpretation, the stronger summer monsoons from the southeast played the major role in magnetic fabric orientation in the studied west and central parts of the Chinese Loess Plateau. The AMS was generated during the rainy summer monsoon when the sedimentary particles including magnetite were rearranged, settled, and fixed. We reconstruct the summer paleomonsoon routes for the last 130 kyr. These winds prevail from SE to NW but appear to be affected by regional topographic factors. Evidence in the world’s ocean current system indicates an abrupt cooling from 34.1 to 33.6 Ma across the Eocene-Oligocene boundary (EOB) at 33.9 Ma. I describe and date with magnetostratigraphy a section from the north Junggar Basin (Burqin section). Three fossil assemblages revealed through the EOB (34.8, 33.7, and 30.4 Ma) demonstrate that perissodactyl faunas were abruptly replaced by rodent/lagomorph-dominant faunas during climate cooling, and the changes in mammalian communities were accelerated by aridification in central Asia. Paleomagnetic studies of two sections of the northern Junggar Basin, China, are presented from Burqin and Tieersihabahe. Our paleomagnetic results demonstrate counterclockwise tectonic rotations in Burqin and Tieersihabahe (–17.2 ± 9.6° and –11.8 ± 6.1°, respectively) as well as considerable northward latitudinal displacement (12.2 ± 6.5° and 9.7 ± 4.1°, respectively) with respect to Europe. These results are consistent with the motions of contiguous blocks in the same geological time intervals (India, north and south China, Tarim, Amuria, and Kazakhstan). No significant intracontinental shortening or vertical-axis rotation is observed for the Junggar block from 40 Ma to 20 Ma. Our results reveal that the major compression and rotation between Junggar and northern Europe occurred after 20 Ma due to continuous penetration of India into Asia. We interpret the uplift of the Altay Mountains and the formation of the Lake Baikal rift system to be due to such intracontinental compression and relative rotations. / Geophysics

I use Synthetic Aperture Radar Interferometry (InSAR) to study the present deformation in the Western Basin and Range and Basin and Range - Sierra Nevada transition. I process 350 SAR data over 190·103 km2 for the period 1992 to 2002. Both stacking and time series processing were applied to produce precise (mm/yr) and high-resolution velocity map for the area. Two new processing techniques have been developed. The first technique solves for the long wavelength ambiguities of the InSAR derived velocity map that arise due to uncertainty in the orbital parameter of the satellite. The technique assimilates continuous GPS data into the InSAR time-series processing. The second technique extracts the horizontal and vertical components of the deformation field from two adjacent radar tracks. I applied stacking to study the transient deformation across the Central Nevada Seismic Belt and interseismic strain accumulation across the Eastern California Shear Zone. I show that the current deformation across the Central Nevada Seismic Belt can be explained by a combination of inter-seismic, post-seismic and anthropogenic deformation. The Post-Seismic deformation is associated with visco-elastic relaxation of the Earth's mantle in response to a centennial earthquake sequence of five ~M7 earthquakes along the Central Nevada Seismic Belt. The anthropogenic deformation is a response of the bedrock to water withdrawal in support of mining activity. A more evolved time-series approach that solves for orbital errors is applied across the Eastern California Shear Zone. The study shows that the Hunter Mountain - Panamint Valley fault system accommodates ~5 mm/yr, a faster rate than geological averages. The region of strain accumulation is a narrow band of ~10 km centered on the Hunter mountain fault, and indicates a very shallow locking depth in agreement with an active low angle normal fault system.

The southern and central Appalachian foreland fold-thrust belt comprises a series of orogen -scale curves that extend from Alabama to New York. One of these is the Tennessee salient, a foreland-convex curve that extends from Cartersville, Georgia, to Roanoke, Virginia. Development of a kinematic model for deformation in the salient has been hindered by a paucity of penetrative deformation in this generally low temperature, low volume-loss portion of the orogen. Industry seismic reflection lines provide greater resolution of subsurface geometry of both the basement surface and the overlying fold-thrust belt, confirming some previous interpretations and changing others. A series of cross sections based on the seismic reflection data incorporates the improved understanding of basement geometry, as well as new interpretations of fold-thrust belt structures such as a sub-thrust detachment fold along the western margin of the Valley and Ridge, a smaller detachment fold along the Cumberland Escarpment, and a duplex below the Knoxville sheet in southeastern Tennessee. The cross sections, combined with recently published analyses of calcite twin strain and paleomagnetic data around the salient, provide sufficient data to develop a new palinspastic reconstruction method and to propose a kinematic model for development of the salient. The basis of the reconstruction method is, in areas where the front of the indenter is oriented oblique to transport, the maximum shortening direction and particle displacement paths are also oblique to the bulk transport direction. Cross sections, kinematic indicators, and palinspastic reconstructions suggest that the Tennessee salient is a primary arc formed by a combination of uniform displacement in a single direction and transport-parallel simple shear (plane strain), that most major faults formed initially curved in front of the irregularly shaped Blue Ridge-Inner Piedmont indenter, and that transport in the fold-thrust belt may have occurred by plan view movement on networks of minor faults, which permitted forelandward propagation of the curved faults without significant rotation. Although the technique does not provide a unique solution, the resulting palinspastic restoration is kinematically admissible and geometrically reasonable. So, it may improve palinspastic restorations of facies in basins with no vertical axis rotations and minimal penetrative strain. Attachments are in PDF format and may be opened with Adobe Reader™.

Kinematic analysis and field mapping of the Homestake shear zone (HSZ) and Slide Lake shear zone (SLSZ) in central Colorado provide new evidence for strain partitioning in the mid-crust at ~1.4 Ga. The northeast-striking, steeply dipping HSZ comprises a ~10-km-wide set of anastomosing ductile shear zones and pseudotachylyte-bearing faults. Approximately 3-km south of the HSZ, the north-northeast-striking, shallowly dipping mylonites of the SLSZ form three 1-10-m-thick shear zone splays. Both top-up-to-the-northwest and top-down-to-the-southeast shear sense are recorded in the SLSZ and HSZ. Oblique stretching lineations in both shear zones show vertical (top-down-to-the-southeast and top-up-to-the-northwest) and dextral movement occurred during mylonite development. Quartz and feldspar deformation mechanisms and quartz [c] axis lattice preferred orientation (LPO) patterns are consistent with deformation temperatures ranging from ~280-500°C in the HSZ to ~280-600°C in the SLSZ. Mean kinematic vorticity and quartz [c] axis LPOs for parts of each shear zone suggest plane and non-plane strain general shear with contributions of 47-69% pure shear and 31-53% simple shear. Based on micro- and mesoscale kinematics along with mean kinematic vorticity values and deformation temperature estimates, we propose that HSZ and SLSZ formed during strain localization and partitioning within a mid-crustal transpressional shear zone system that involved subvertical shuffling at ~1.4 Ga.

Thesis (Ph. D.)--Ohio State University, 2006. / Title from first page of PDF file. Includes bibliographical references (p. 162-176).

Ce travail a consisté à restaurer deux chaînes d'avant-pays arquées imbriquées situées dans la partie frontale des Alpes franco-suisses: les Chaînes Subalpines Septentrionales (CSS) et le Jura à leur front. Le Jura a été rétrodéformé à l'aide d'un logiciel de restauration en 3D UNFOLD et les CSS sur la base de coupes sériées. La restauration 3D du Jura indique champ de déplacement vers le front de l'arc. Nous montrons que le décollement du Jura doit s'enraciner dans des chevauchements crustaux supposés ou dans le décollement des CSS. Les données sur la chronologie des déformations ne permettant pas de distinguer les deux hypothèses, nous utilisons les résultats de la restauration des CSS pour proposer un nouveau modèle pour la propagation des déformations dans les Alpes Externes franco-suisses entre l'Oligocène et le Pliocène.