Th. doct.--Sci. de la terre et de l'eau--Montpellier 2, 2001. / Mention parallèle de titre ou de responsabilité : [@Contribution à l'étude de la terminaison ouest de la subduction des Ryukyus au niveau de la collision active arc-continent à Taiwan] : apports de la sismique réflexion et de la relocalisation hypocentrale. Bibliogr. p. 271-279. Résumés en français et en anglais.

Dissertation--Fachbereich Geowissenschaften--Mainz--Johannes Gutenberg Universität, 2004. Thèse de doctorat--Terre solide, géodynamique--Montpellier II, 2004. / Mention parallèle de titre ou de responsabilité : Contraindre l'évolution tectonique des systèmes de faille extensive dans les Cyclades (Grèce) en utilisant la thermochronologie de basse température. Thèse soutenue en co-tutelle. Bibliogr. Titre provenant de l'écran-titre.

Thesis (Ph. D.)--University of Washington, 2003. / Vita. Includes bibliographical references (p. 127-141).

The Franciscan Complex and Coast Range Ophiolite (CRO) are juxtaposed along the Coast Range Fault (CRF), which is steeply dipping to near vertical in the Stonyford area. The CRF has been interpreted as a thrust fault and a normal fault but no kinematic data has been presented for the Stonyford region. The CRO locally is internally disrupted and can be described as an ophiolitic mélange. Near Stonyford, serpentinites are in contact with Great Valley sediments to the east and with Franciscan rocks to the west. Mafic volcanics are only found at a few localities with some chert and gabbros. Massive serpentinites form most of the southernmost transect while foliated serpentinite mélange dominates the northern transects. Six structural geologic transects were made in the CRO along National Forest Service roads in the Mendocino National Forest near the Stonyford, California area. Data were collected from 21 road cuts totaling approximately 10 kilometers of CRO exposure. Exposures were typically two meters high with the main exception along Goat Mountain Road where the serpentinite was massive with outcrop heights of 10 to 20 meters. Fault plane orientations and sense of slip (where recognizable) were measured for all faults traceable for more than 10 cm. A total of 1,108 faults were measured, 414 contained lineations, and 326 had lineations with steps which determine sense of slip. Approximately two-thirds of the faults with full kinematics had evidence for normal offset. About 25% recorded reverse offset, mostly steeply dipping surfaces. Strike-slip faulting, both right and left-lateral, accounted for 10% of the data. The ascent of the Franciscan and CRO, and upturning of the Knoxville Formation (Great Valley Group) to near vertical attitude was mostly a result of normal faulting. The Great Valley Group strata, with little internal offset by faulting, indicates the disruption of the CRO near Stonyford predates most of the normal faulting. This is consistent with pre-subduction deformation of the CRO in an oceanic fracture zone. / text

Oxygen isotopes and major and trace element geochemistry have been used to evaluate the geochemical and tectonic history of a Franciscan hornblende-amphibolite and a eclogite block from Ring Mountain, Tiburon and three eclogite/blueschist blocks from Jenner Beach, California, all blocks have experienced varying amounts of retrogression. Relative to the presumed basaltic protolith, enrichments in large ion lithophile elements (LILEs) indicate interaction with sediment derived fluids in the retrograde eclogite and retrograde blueschist samples and high Mg, Cr, and Ni in actinolite rind indicate interaction with ultramafic rock. The [delta]¹⁸O values of chlorite from the Ring Mountain hornblende-amphibolite and the eclogite block have a narrow range of [delta]¹⁸O values (+7.7-8.2%₀, n=8) and actinolite from actinolite rind on the eclogite block from Ring Mountain and the blueschist/eclogite blocks from Jenner Beach are (+7.8-8.5%₀, n=5). Chlorite-actinolite geothermometry yields temperatures of 200-280°C for actinolite rind formation. Additionally, the [delta]¹⁸O values of both chlorite and actinolite at these temperatures indicates equilibrium with the measured value of Tiburon serpentinites, (7.6 to 8.1%₀, n = 3 Wenner and Taylor, 1974). Oxygen isotope analyses of garnet mineral separates from the eclogite and hornblende-amphibolite from Ring Mountain have [delta]¹⁸O values of +6.8±0.3%₀ (n=7), and +8.2±0.2%₀ (n=7), respectively. Garnets from the three eclogite/blueschist blocks at Jenner Beach have a [delta]¹⁸O value of +9.8±0.7%₀, (n=23). The difference in [delta]¹⁸O values of garnets between the high-grade blocks is likely due to in situ hydrothermal alteration of the seafloor basalt prior to subduction. The geochemical trends can be explained by a model in which during the early stages of subduction pieces of altered oceanic crust are detached from the downgoing slab and incorporated into the mantle wedge soon after reaching peak eclogite or amphibolite facies conditions. As subduction continues, the hanging wall cools and fluids released from subducted sediments infiltrate the overlying mantle wedge. As the blocks cool they develop a retrograde blueschist facies overprint under relatively static conditions. With cooling of the hanging wall and infiltration of sedimentary fluids, serpentinization induces reaction between the blocks and surrounding mantle wedge and Mg-rich actinolite rind is formed. The blocks are then plucked from the mantle wedge and incorporated into the subduction channel where they flow back to the surface via corner flow. / text

No description available.

This dissertation explores subduction zone-related deformation both on short time scales in the form of subduction zone earthquakes and over larger time and geographical scales in the form of subduction rollback or detachment of the subducting lithosphere. The study presented here is composed of two parts. First, we analyzed the source-rupture processes of the April 1, 2007 Solomon Islands Earthquake (Mw=8.1) using a body-wave inversion technique. Our analysis indicated that the earthquake ruptured approximately 240 km of the southeast Pacific subduction zone in two sub-events.In the second part of this study, we used shear-wave splitting analysis to investigate the effects of the subducting African lithosphere on the upper-mantle flow field beneath the Anatolian Plate in the Eastern Mediterranean region. Our shear-wave splitting results are consistent with relatively uniform southwest-directed flow towards the actively southwestward-retreating Aegean slab. Based on spatial variations in observed delay times we identified varying flow speeds beneath Anatolia and we attribute this variation to the differential retreat rates of the Aegean and the Cyprean trenches.Finally, we used teleseismic P-wave travel-time tomography to image the geometry of the subducting African lithosphere beneath the Anatolia region. Our tomograms show that the subducting African lithosphere is partitioned into at least two segments along the Cyprean and the Aegean trenches. We observed a gap between the two segments through which hot asthenosphere ascends beneath the volcanic fields of western Anatolia. Our results show that the Cyprean slab is steeper than the Aegean slab. We inferred that this steep geometry, in part, controls the flow regime of asthenosphere beneath Anatolia causing variations in flow speeds inferred from shear-wave splitting analysis.

This dissertation explores the uses for data collected at broadband seismic stations to investigate upper mantle structures. In the Barents Sea region, we use seismic waveform modeling on data collected from arrays in Norway and Finland to investigate the nature of the Hales discontinuity in this area. We find that the unusually high velocities required by the move-out of the diffracted first arrival requires a discontinuity below the Moho, which we believe is probably caused by a phase transition from spinel to garnet peridotite. In Chile and Argentina, we use data collected during the Chile Argentina Geophysical Experiment to perform a regional travel time tomography in order to investigate the nature of the mantle above this unusual subduction zone. The northern half of the study area (between 30° and 33°S) is characterized by the central Chilean flat slab segment, where the descending Nazca slab dives to 100 km depth and then flattens, traveling horizontally for hundreds of kilometers before resuming its descent into the mantle. The Nazca plate in the southern half of the study area has a relatively constant dip of about 30°. The southern half exhibits normal arc volcanism roughly above the 100 - 125 km contours of the downgoing slab. The northern half has had no active volcanism in the past 2 Ma, and underwent an eastward displacement of arc volcanism beginning ~10 Ma. The northern half is also remarkable for the basement-cored uplifts of the Sierras Pampeanas. Our study of the upper mantle above the southern half indicates low P wave velocities, low S wave velocities, and high Vp/Vs ratios below the arc, consistent with partial melt. Above the flat slab segment we find low Vp, high Vs, and low Vp/Vs ratios. While the nature of the material responsible for these velocities cannot be uniquely determined, the velocities indicate it must be dry, cold, and depleted. In the transition from flat to normal subduction geometries, we find velocities consistent with frozen asthenosphere, which may have been displaced by the advancing flat slab during the Miocene.

Au travers de l'étude pétrologique, géochronologique et structurale du dôme éclogitique du Tso Morari (E-Ladakh, Himalaya), les processus d'exhumation des roches de HP-BT sont discutés. La découverte d'éclogites à glaucophane, de métasédiments à jadéite-chloritoïde et de métagranites éclogitisés, implique la subduction du dôme du Tso Morari à plus de 70 km de profondeur (20 ± 3 kbar ; 580 ± 50°C). Son exhumation s'accompagne d'une décompression quasi-isothermale jusqu'à 40-30 km. Puis elle est associée à une augmentation de température (630 ± 30°C), et s'achève dans le faciès des Schistes Verts. Les unités adjacentes au dôme du Tso Morari sont peu métarmorphiques (faciès Schistes Verts ) et de nature différente. La chimie des basaltes montre une origine d'avant arc pour l'ophiolite de Nidar et d'OIB pour les unités de Drakkarpo et Ribil ; les roches basiques du Tso Morari sont au contraire des tholéiites continentales. L'origine indienne du Tso Morari est confirmée par les âges des orthogneisses à 458-457 Ma en Sm/Nd et Rb/Sr. La subduction de la marge indienne, est datée à 60-55 Ma par U-Pb et Lu-Hf. L'exhumation débute rapidement (≥ 4mm.an-1) entre 55 ± 7 Ma (Sm-Nd sur Grt-Gln-RT) et 48-45 Ma (Rb/Sr et 39Ar/40Ar sur des métapélites rétromorphosées), en contexte de subduction. L'exhumation se poursuit plus lentement (≈ 2 mm.an-1) de 48-45 Ma à 30 ± 1 Ma (âges 39Ar/40Ar sur micas), en contexte de collisions. Les structures (D1-D2), liées à l'extrusion verticale du dôme, sont indépendantes de celles des unités adjacentes. La transition entre D1, témoin d'un raccourcissement horizontal, et de D3 associé à du raccourcissement vertical , passe par un régime de déformation en constriction (D2). Les changements pétrologiques, structuraux et géochronologiques sont corrélés à des changements de géométrie à l'échelle des plaques. L'exhumation du Tso Morari débute par extrusion verticale à travers le coin mantéllique serpentinisé, en contexte de subduction continentale oblique. Puis le dôme est exhumé plus lentement à travers la croûte, à la faveur du sous-plaquage du cristallin du Haut Himalaya sous le Tso Morari, provoquant un épaississement crustal important, en contexte de collision. A partir de cette évolution, defférents modèles d'exhymations sont discutés

The development and activity of submarine canyons on continental margins is strongly influenced by temporal and spatial changes in sediment distribution associated with orbitally-forced sea-level cyclicity. On active margins, canyons are also strongly influenced by tectonic processes such as faulting, uplift and earthquakes. Within this framework the role of mass-wasting processes, including sediment failures, bedrock landslides and sediment gravity flows, are to: 1) transport material across the slope; 2) act as intra-slope sediment sources; and 3) shape seafloor morphology. In this project the seafloor-landscape signatures of tectonic and geomorphic processes are analysed to interpret the development of submarine canyon morphology on active margins. Datasets include high-resolution bathymetry data (Simrad EM300), multichannel seismic reflection data (MCS), high-resolution 3.5 kHz seismic reflection data, sediment cores, and dated seafloor samples. High-resolution bathymetric grids are analysed using techniques developed for terrain-roughness analysis in terrestrial landscapes to objectively map and interpret features related to seafloor mass-wasting processes. The Hikurangi subduction margin of New Zealand provides world-class examples of the control of tectonic and sedimentary processes on margin development, hosting multiple examples of deeply-incised canyon systems across a range of scales. Two main study sites, in Poverty Bay and Cook Strait, provide examples of canyon formation. From these examples conceptual and representative models are developed for the spatial and temporal relationships between active tectonic structures, geology, sediment supply, slope- and shelf-incised canyons, slope gully systems, and bedrock mass failures. The Poverty Bay site occurs on the subduction-dominated northern Hikurangi Margin, where the ~3000 km² Poverty re-entrant hosts the large Poverty Canyon system, the only shelf-break-to-subduction-trough canyon on the northern margin. The geomorphic development of the re-entrant is affected by gully development on the upper slope, and multi-cubic-kilometre-scale submarine landslides. From this site the study focuses on the initiation and development of upper-slope gullies and the role of deep-seated slope failure in upper-slope evolution. The Cook Strait site occurs on the southern Hikurangi Margin in the subduction-to-strike-slip transition zone. The 1800 km² Cook Strait Canyon incises almost 50 km into the continental shelf, with a multi-branching canyon head converging to a deeply slope-incised meandering main channel fed by multiple contributing slope canyons. Other medium-sized canyons are incised into the adjacent continental slope. Fluvial sediment supply to the coast is relatively low on the southern margin, but Cook Strait is subject to large diurnal tidal currents that mobilise sediment through the main strait area. Prior to the morphostructural analysis of the Cook Strait and Poverty study sites a revision of the tectonic structure was undertaken. In Cook Strait a revision of the available fault maps was undertaken as part of a wider, related tectonic study of the central New Zealand region. In Poverty Bay very limited prior information was available, and as part of this study the structure and stratigraphy of the entire shelf and upper slope has been interpreted. On active tectonic margins submarine canyons respond to tectonics at: 1) margin-setting scales relating to their ability to become shelf incised; 2) regional scales relating to canyon-incision response to base-level perturbations; and 3) local scales relating to propagating structures affecting canyon location and geometry. Interpretation of the spatial distribution of fluid vent sites, gully development and landslide scars leads to the conclusion that seepage-driven failure is not a primary control on the widespread instances of gully formation and landslide erosion affecting structurally-generated relief across the margin. Rather, the erosion of tectonic ridges is dominated by tectonics by: slope oversteepening; weakening of the rockmass in fault-damage zones; and triggering of slope failure by earthquake-generated cyclic loading. Deep-seated mass failures affect numerous aspects of submarine landscapes and play a major role in the enlargement of canyon systems. They enable the development of slope gully systems and represent a major intra-slope sediment source. Quantitative morphometric analysis together with MCS data indicate that landslides may evolve to be active complexes where landslide debris is remobilized repeatedly, analogous to terrestrial-earthflow processes. This process has not previously been documented on submarine slopes. A model is presented for the evolution of active margin canyons that contrasts highstand and lowstand canyon activity in terms of channel incision, sedimentary processes and slope-erosion processes. During sea-level highstand intervals, canyons become decoupled from their terrestrial/coastal sediment-supply source areas, while during sea-level lowstand intervals, canyons are coupled to fluvial and littoral sediment-supply sources, and top-down (i.e. shelf-to-lower-slope) sediment transport and channel incision is active. Canyon-head areas are incision dominated during the lowstand while mid to lower canyon reaches experience both a transient increase in sediment in storage and canyon-fill degradation and incision into bedrock. Tectonics influences the canyon landscape through both uplift-controlled perturbations to canyon base-levels and earthquake-triggering of mass movement. Following sea-level rise the sediment supply to canyon heads will be switched off at a certain threshold sea level. From this point canyon heads become aggradational. Mid to lower canyon reaches continue to incise due to continuing tectonic uplift and earthquake-triggered slope instability. Knickpoints are propagated up channel and excavate canyon and sub-canyon channels from the bottom up. Thus, while top-down infilling of non-coupled canyons occurs during sea-level highstands, the lower reaches of active margin canyons continue to incise due the influence of tectonic processes.