abstract: The Himalaya are the archetypal example of a continental collision belt, formed by the ongoing convergence between India and Eurasia. Boasting some of the highest and most rugged topography on Earth, there is currently no consensus on how climatic and tectonic processes have combined to shape its topographic evolution. The Kingdom of Bhutan in the eastern Himalaya provides a unique opportunity to study the interconnections among Himalayan climate, topography, erosion, and tectonics. The eastern Himalaya are remarkably different from the rest of the orogen, most strikingly due to the presence of the Shillong Plateau to the south of the Himalayan rangefront. The tectonic structures associated with the Shillong Plateau have accommodated convergence between India and Eurasia and created a natural experiment to test the possible response of the Himalaya to a reduction in local shortening. In addition, the position and orientation of the plateau topography has intercepted moisture once bound for the Himalaya and created a natural experiment to test the possible response of the range to a reduction in rainfall. I focused this study around the gently rolling landscapes found in the middle of the otherwise extremely rugged Bhutan Himalaya, with the understanding that these landscapes likely record a recent change in the evolution of the range. I have used geochronometric, thermochronometric, and cosmogenic nuclide techniques, combined with thermal-kinematic and landscape evolution models to draw three primary conclusions. 1) The cooling histories of bedrock samples from the hinterland of the Bhutan Himalaya show a protracted decrease in erosion rate from the Middle Miocene toward the Pliocene. I have attributed this change to a reduction in shortening rates across the Himalayan mountain belt, due to increased accommodation of shortening across the Shillong Plateau. 2) The low-relief landscapes of Bhutan were likely created by backtilting and surface uplift produced by an active, blind, hinterland duplex. These landscapes were formed during surface uplift, which initiated ca. 1.5 Ma and has totaled 800 m. 3) Millennial-scale erosion rates are coupled with modern rainfall rates. Non-linear relationships between topographic metrics and erosion rates, suggest a fundamental difference in the mode of river incision within the drier interior of Bhutan and the wetter foothills. / Dissertation/Thesis / Ph.D. Geological Sciences 2014

Des études récentes menées dans la région de Sarpang au sud du centre du Bhoutan estiment un taux de glissement Holocène de 20,8 +/- 8,8 mm/an sur le chevauchement frontal himalayen (TFT). Cette valeur est basée sur un taux de surrection moyen mesuré de 8,8 +/- 2,1 mm/an et en supposant pour ce chevauchement un pendage constant de 25° +/- 5°. La géométrie des failles est un paramètre clé dans l’estimation de la vitesse de glissement et donc dans l’évaluation de l’aléa sismique. Dans le cadre de ce travail, nous avons utilisé une approche géophysique de proche surface afin d’estimer précisément la géométrie de ce chevauchement.Nous avons déployé des profils géophysiques dans trois sites clés le long de la frontière sud du Bhoutan. La première zone d'étude se trouve à Sarpang, une petite ville située au centre du Bhoutan où nous avons effectué des mesures gravimétriques, sismiques et électriques. Le deuxième site est situé à Phuentsholing dans le sud-ouest du Bhoutan, où nous avons effectué des mesures gravimétriques et de résistivité électrique. Le troisième site est situé entre Sarpang et Phuentsholing, à Lhamoizingkha dans le district de Dagana.Excepté pour la région de Lhamoizingkha, une approche d'inversion stochastique a été adoptée pour analyser des données géophysiques collectées. Contrairement aux approches couramment utilisées basées sur la recherche du modèle le plus simple, les principaux avantages de cette approche sont sa capacité (1) à mieux estimer la géométrie des zones de discontinuité car aucun lissage n'est appliqué, (2) à fournir une mesure des incertitudes sur le pendage obtenu et (3) à permettre une analyse des relations possibles entre les propriétés géométriques et celles du milieu (résistivité électrique, vitesse ou densité).Les résultats d'inversion stochastique du site de Sarpang montrent un TFT qui se caractérise par une géométrie en plat-rampe-plat avec un pendage vers le nord d'environ 20°-30° dans la partie la plus superficielle (profondeur < 5 m), un pendage fort de 70° entre 5 m et 40 m de profondeur et un l'aplatissement avec un pendage de 20° au-delà de 40 m. Ces nouveaux résultats nous permettent d'estimer un taux minimal de glissement de 10 +/- 2 mm/an sur le TFT, soit environ 60% des 17 mm/an associés au taux de convergence GPS moyen obtenu en champ lointain. Sur la base de ces contraintes, il apparait donc qu’on ne puisse pas exclure la possibilité que la déformation soit distribuée sur plusieurs failles, comprenant le TFT, mais également d’autres chevauchements comme le MBT (au nord) ou le FBT (au sud). De plus, en supposant un taux de glissement constant, les variations de pendage obtenues induisent des variations du taux de surrection en fonction de la distance au TFT. Cela souligne les faiblesses des hypothèses couramment faites pour estimer les taux de glissement Holocène sur les failles sismogènes : (1) pendage constant estimé uniquement à partir des observations de surface et (2) estimations du taux de surrection en supposant une surrection identique pour une terrasse fluviale donnée.Contrairement à Sarpang, à Phuentsholing le TFT correspond au chevauchement frontal himalayen (MFT). Sur ce site, l’étude préliminaire que nous avons menée suggère un MFT ayant une géométrie de faille listrique. Des mesures de datations doivent maintenant être effectuées pour estimer le taux de glissement sur le MFT dans cette zone. Dans la région de Lhamoizingkha, l'emplacement exact du MFT n'est pas connu. Nos résultats préliminaires suggèrent une géométrie complexe de la trace de la faille en surface et indiquent que le MFT est situé plus au nord de la ligne de résistivité déployée dans cette zone. À l'instar du site de Phuentsholing (mais contrairement à Sarpang), nous avons observé que le MFT était la structure la plus frontale et que l’essentiel de la convergence dans cette zone pouvait être accommodé par le MFT, comme semble le suggérer les observations GPS. / Recent studies based on surface observations from Sarpang area in southern-central Bhutan have estimated the Holocene slip rate of 20.8+/-8.8 mm/year. This value is based on a mean vertical uplift rate of 8.8+/-2.1 mm/year and assuming a constant frontal thrust dip angle of 25°+/-5° extrapolated from structural measurements. Since geometry of the fault is a key parameter for discerning the slip rate and its associated seismic hazard assessment, we employed near-surface geophysical approach to accurately constrain the Topographic Frontal Thrust (TFT) geometry at shallow depth. Based on proven effectiveness of near-surface geophysical techniques for studying active faults, we adopted gravity, seismic and electrical resistivity tomography.We deployed geophysical profiles at three key sites along the southern frontal areas of the Bhutan Himalayas. The first study area is in Sarpang, a small town located in southern-central Bhutan where we performed all three geophysical methods adopted. The second site is located in Phuentsholing in the south-western Bhutan, where we performed gravity and electrical resistivity survey. The third site is located between Sarpang and Phuentsholing, in the sub-district of Lhamoizingkha under Dagana district.A stochastic inversion approach was adopted to perform analysis of geophysical data collected from the above sites expect for Lhamoizingkha area. Unlike commonly used approaches based on search for the simplest model, the main advantages of this approach include its ability (1) to assess the fault geometry because no smoothing is applied, (2) to provide a measurement of the uncertainties on the obtained dip angle and (3) to allow trade-off analysis between geometric and either electrical resistivity, velocity or density properties.The stochastic inversion results from Sarpang site show a TFT that is characterized by a flat and listric-ramp geometry with a north dipping dip angle of ca 20°-30° at the upper depth of 0-5 m, steeply dipping angle of 70° in the middle 5-40 m depth and flattening with a dip angle of 20° at deeper depths. These new results allow us to estimate a minimum overthrusting slip rate of 10+/-2 mm/year on the TFT, which is about 60% of the far-field GPS convergence rate of ca 17 mm/year. Based on these constraints we propose that, in Sarpang site, significant deformation partitioning on different faults including the TFT, the Main Boundary Thrust (MBT) and the Frontal Back Thrust (FBT) cannot be ruled out. More importantly, assuming a constant slip rate, the dip angle variations constrained from the present study, corresponds to variations in the uplift rate with distance from the TFT. This, therefore, emphasizes the drawbacks in assuming constant dip angle measured from surface observations and uplift rate estimates based on terrace dating only at the front, which may significantly bias the slip rate estimation.Unlike in Sarpang, the TFT corresponds to the Main Frontal Thrust (MFT) in Phuentsholing. At this site a preliminary study suggests a MFT characterized by a flat and listric-ramp geometry. With additional terrace dating information, slip rate for the Phuentsholing area will be performed in a near future. Overall based on the stochastic inversion results, we propose a MFT geometry similar to that observed in Sarpang but with possible lateral variations in terms of deformation partitioning. In Lhamoizingkha area, the exact location of the MFT is not known. Our preliminary results suggest a complex fault trace and indicate that the MFT is located further north of the current resistivity line deployed in this area. Similar to Phuentsholing site (but contrary to Sarpang), we observed that the MFT is the most frontal structure and therefore most of the convergence in the area could be accommodated by the MFT, which is also in agreement with GPS observations.

This dissertation investigates the evolution of continental orogenic systems in Central Asia during and between pre-collisional plate convergence (Cordilleran-style orogenesis), syn-collisional plate convergence (collisional orogenesis), and post-collisional tectonic processes within the scope of closing Paleo-Asian and Tethyan ocean basins. A brief introductory chapter outlines the scope and context of the research. Appendix A focuses on the Late Paleozoic closure of the Turkestan ocean basin and subsequent collision between the Karakum–Tarim and Kazakh–Kyrgyz terranes in the South Tian Shan, within the scope of the final amalgamation of the Mesoproterozoic–Permian Central Asian Orogenic Belt. Appendix B focuses on late Cenozoic syn-collisional exhumation of gneiss domes in the India–Asia collision, which is a component of the Triassic–recent Alpine–Himalayan orogenic belt. Abstracts of the results are provided in the respective appendices.

Identifying tectonically active faults and quantifying rates of movement is a key challenge in the Earth Sciences, in addition to this the interactions between active faulting and the landscape, specifically involving the fluvial network, is a relatively new area of study. Previous work has highlighted the value of understanding how the fluvial network responds to active tectonics, showing that a comprehensive understanding of the dynamic relationship between fluvial geomorphology and active tectonics is an important next step in geological research. This study presents new information about the poorly constrained Quaternary tectonic history of the Gediz Graben, Turkey, providing the first quantification of rates of movement of the key fault array that presently controlling graben topography. The fluvial network has been investigated and the data has been used in order to add resolution to the tectonic history for the fault array, allowing for the quantification of post-linkage throw rates. The study then investigates the key controls on the behaviour of the fluvial network that cross the active topography building fault array in the Gediz Graben. This study shows that there has been a linkage event occurring between 0.6 – 1 Ma, involving the three segments of the graben bounding fault array. The pre- and post-linkage throw rates are then extrapolated using data derived from the fluvial network, showing a faulting enhancement factor of 3 at the centre of the fault array, with the throw rate at the centre of the array predicted to have increased from a pre-linkage rate of 0.6 ± 0.1 mm/yr to a rate of 2 ± 0.2 mm/yr. This research provides evidence that the fluvial network can be used in conjunction with other types of evidence to provide a greater resolution tectonic history. Using both digital data and field studies this research presents an examination of the factors that influence the behaviour of bedrock rivers undergoing perturbation due to tectonics. Factors such as drainage area, tectonic throw rates and lithology have been investigated and the complicated interactions of these variables with the fluvial system have been quantified. This study shows that the bedrock rivers are a significant source of information about tectonics, but further work is needed to resolve quantitatively how various factors influence how rivers adjust to tectonic perturbation, in a variety of tectonic situations, in order to enable river to be used as a primary tool for deriving information about tectonics.

Magister Scientiae - MSc / Following successful discovery and production of hydrocarbons, Gabon is one of the key hydrocarbon target countries in Africa. Located in the Lower Congo Basin, the study area is based in Etame Marin Permit (EMP), which is licensed to VAALCO Energy Inc., and has been producing hydrocarbons since 2002. The currently explored and producing reservoirs are in the pre-salt sandstones of the Aptian Gamba Formation, charged with hydrocarbons sourced from the syn-rift lacustrine shale of the pre-Aptian Melania Formation. With the aim of finding potential petroleum plays in the post-salt successions and by using 3D prestack depth migration (PSDM) seismic sections and wireline logs, a detailed study of the post-Aptian stratigraphy and salt tectonics of the EMP was undertaken. Eight distinct reflectors were identified based on gamma ray signatures, stratal terminations and isopach trends. Sediment distribution patterns and the relative sea level history of the succession were determined by applying principles of sequence stratigraphy and salt tectonics. Furthermore, two potential plays have been outlined in the post-salt carbonates of the Albian Madiela Formation as well as in sandstones of the Turonian Azile Formation. These reservoirs might have been charged with hydrocarbons from the pre-salt shale of the Melania Formation and/or potentially also enriched from the Albian and Cenomanian shales. For these post-salt hydrocarbon reservoirs to be charged by the pre-salt source rocks, windows within the extensive evaporitic sealing of the Aptian Ezanga Formation were required. 3D PSDM seismic sections attest that diapirism of the Aptian salt unit generated ample hydrocarbon migration pathways from the pre-salt source rocks to post-salt reservoirs. Five well-developed potential salt windows have been identified, two of which have good probability to have facilitated the upward migration of hydrocarbons, because these salt windows are located up dip of oil producing wells. However, even if hydrocarbons are found in the post-salt reservoirs, similarly to the Yombo Field (located offshore Congo, south of the EMP), these shallow reservoirs in the EMP are likely to produce heavy oils due to biodegradation.

The method of magnetotellurics (MT) uses surface measurements of naturally-occurring electromagnetic fields to investigate the conductivity distribution within the Earth. In many interpretations it is adequate to represent the conductivity structure by a one-dimensional (1-D) model. Inferring information about this model from surface field measurements is a non-linear inverse problem. In this thesis, linearized construction and appraisal algorithms are developed for the 1-D MT inverse problem. To formulate a linearized approach, the forward operator is expanded in a generalized Taylor series and second-order terms are neglected. The resulting linear problem may be solved using techniques of linear inverse theory. Since higher-order terms are neglected, the linear problem is only approximate, and this process is repeated iteratively until an acceptable model is achieved. Linearized methods have the advantage that, with an appropriate transformation, a solution may be found which minimizes a particular functional of the model known as a model norm. By explicitly minimizing the model norm at each iteration, it is hypothesized that the final constructed model represents the global minimum of this functional; however, in practice, it is difficult to verify that a global (rather than local) minimum has been found. The linearization of the MT problem is considered in detail in this thesis by deriving complete expansions in terms of Fréchet differential series for several choices of response functional, and verifying that the responses are indeed Fréchet differentiable. The relative linearity of these responses is quantified by examining the ratio of non-linear to linear terms in order to determine the best choice for a linearized approach. In addition, the similitude equation for MT is considered as an alternative formulation to linearization and found to be inadequate in that it implicitly neglects first-order terms. Appropriate choices of the model norm allow linearized inversion algorithms to be formulated which minimize a measure of the model structure or of the deviation from a (known) base model. These inversions construct the minimum-structure and smallest-deviatoric model, respectively. In addition, minimizing I₂ model norms lead to smooth solutions which represent structure in terms of continuous gradients, whereas minimizing I₁ norms yield layered conductivity models with structural variations occurring discontinuously. These two formulations offer complementary representations of the Earth, and in practice, a complete interpretation should consider both. The algorithms developed here consider the model to be either conductivity or log conductivity, include an arbitrary weighting function in the model norm, and fit the data to a specified level of misfit: this provides considerable flexibility in constructing 1-D models from MT responses. Linearized inversions may also be formulated to construct extremal models which minimize or maximize localized conductivity averages of the model. These extremal models provide bounds for the average conductivity over the region of interest, and thus may be used to appraise model features. An efficient, robust appraisal algorithm has been developed using linear programming to extremize the conductivity averages. For optimal results, the extremal models must be geophysically reasonable, and bounding the total variation in order to limit unrealistic structure is an important constraint. Since the extremal models are constructed via linearized inversion, the possibility always exists that the computed bounds represent local rather than global extrema. In order to corroborate the results, extremal models are also computed using simulated annealing optimization. Simulated annealing makes no approximations and is well known for its inherent ability to avoid unfavourable local minima. Although the method is considerably slower than linearized analysis, it represents a general and interesting new appraisal technique. The construction and appraisal methods developed here are illustrated using synthetic test cases and MT field data collected as part of the LITHOPROBE project. In addition, the model construction techniques are used to analyze MT responses measured at a number of sites on Vancouver Island, Canada, to investigate the monitoring of local changes in conductivity as a precursor for earthquakes. MT responses measured at the same site over a period of four years are analyzed and indicate no significant changes in the conductivity (no earthquakes of magnitude greater than 3.0 occurred in this period). Conductivity profiles at a number of sites are also considered in an attempt to infer the regional structure. Finally, a method of correcting linearized inversions is developed. The corrections consist of successively approximating an analytic expression for the linearization error. The method would seem to represent a novel and practical approach that can significantly reduce the number of linearized iterations. In addition, a correspondence between the correction steps and iterations of the modified Newton's method for operators is established. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

A study of the dispersion of long-period Rayleigh waves was proposed in order to acquire additional knowledge about the lithospheric structure of the Vancouver Island region. Three portable, long-period seismographs were designed and built to operate in field conditions. An array was established with stations at Victoria, Vancouver and Quadra Island; during six weeks of operation, several earthquakes were recorded, of which two were aligned conveniently with the array. Another network with stations at Ucluelet, Quadra Island and Victoria was set up later; no usable data were recorded. the earthquake record was chosen for analysis, and group-velocity dispersion calculations were begun. Echo resolution on these data and a lack of ether usable records prevented the continuation of the data processing. No conclusions are drawn about the lithospheric structure; however, recommendations are made regarding possible future experimentation with the existing apparatus. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Published paleomagnetic studies have shown that the Oregon Coast Range has rotated 60° clockwise since middle Eocene time, probably by pivoting either during collision of a seamount terrane or during an episode of asymmetric extension within western North America. Eocene sedimentary deposits within the Oregon Coast Range basin, in particular the Tyee Formation, document changes in basin evolution that provide geologic constraints for proposed rotation models. The Tyee Formation comprises an arkosic petrofacies which is different from underlying lithic sandstones that were derived from the adjacent Klamath Mountains. Isotopic study of sandstones of the arkosic petrofacies, including Sm-Nd, Rb-Sr, K-Ar, and ¹⁸O analyses, indicate that much of the sandstone was not derived from the Klamath Mountains or nearby Sierra Nevada. The source area most likely included S-type granites of the Idaho Batholith. Lithofacies within the Tyee Formation include a sandy deltaic system to the south, a thin muddy shelf/slope sequence farther north, and a thick basinal sequence of sandy high-density turbidites that grade northward into low-density turbidites. Absence of facies segregation within the turbidite sequence precludes application of classical deep-sea fan depositional models and forms the basis for the delta-fed submarine ramp model introduced here. Delta-fed submarine ramps are short-lived sandy systems that result from rapid rates of progradation as well as aggradation. Synchronous changes in depositional style, structural deformation, sandstone composition, and rates of tectonic subsidence of the Oregon Coast Range basin are interpreted to record the transition from collisional trench-fill deposition to a subsiding forearc basin. The Tyee Formation was deposited after collision was complete and yet is rotated as much as the seamounts on which it lies; therefore, rotation must have occurred subsequent to collision. Since these sediments were partially derived from the Idaho Batholith region, the Oregon Coast Range probably lay much farther east during deposition and subsequently rotated westward to its present position. Tectonic rotation of the Oregon Coast Range may have resulted from continental extension that began in the Pacific Northwest about 50 Ma. Paleogeographic reconstructions show that basin development was synchronous with regional extension, arc migration, and tectonic rotation throughout the Pacific Northwest.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第22029号 / 理博第4533号 / 新制||理||1651(附属図書館) / 京都大学大学院理学研究科地球惑星科学専攻 / (主査)教授 橋本 学, 教授 福田 洋一, 准教授 深畑 幸俊 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

The present-day kinematics and deformation of the Arabian plate and the southern Red Sea region involves interaction of tectonic and non-tectonic processes including plate subduction, continental collision, seafloor spreading, intraplate magmatism, continental transform faulting, microplate rotation, hydrological loading cycles, and anthropogenic activity. Therefore, good constraints on the rates and directions of relative plate motion, plate boundary locations, and rheological properties in the area are essential to assess seismic and volcanic hazards in the region. In this thesis, I combine Global Navigation Satellite System (GNSS) measurements from over 200 stations with kinematic block modeling to provide updated estimates of the present-day motions of the Arabian plate and the southern Red Sea region. Using the non-rigid residual motions and changes in GNSS station baselines, I provide quantitative constraints on the internal deformation for the Arabian plate at different spatial scales. In addition, I use the GNSS station response to seasonal water exchange in the Red Sea to make inferences of the lithospheric elastic properties beneath Arabia. The GNSS-derived velocity field indicates coherent motion of both the Danakil block in the southern Red Sea and the Arabian plate at present. Current motions in the southern Red Sea region, however, are inconsistent with previous interpretations and require an additional plate boundary in the area. My updated fault slip rates improved earlier estimates limited by the number and spatial distribution of GNSS stations, particularly for the Arabian-Indian plate pair, for which slower right-lateral strike-slip motions are predicted. Non-rigid residual velocities within the Arabian plate interior indicate that large-scale internal deformations are compensated internally. However, at a smaller scale, I identify several localities accommodating significant strain, mostly related to anthropogenic activity. Ground response to surface mass loading associated with water transport in the Red Sea suggests that the Earth’s elastic structure beneath the Arabian plate is 20% to 30% less stiff than global averaged (i.e., AK135-F planetary model). Still, the lithosphere beneath both the Danakil block and the Arabian plate remains strong despite being affected by significant faulting and magmatism associated with the Nubian-Arabian-Eurasian plate interaction.