Thesis (M.S.) in Earth Sciences--University of Maine, 2009. / Includes vita. Includes bibliographical references (leaves 105-111).

Thesis (Masters) -- California Institute of Technology, 1939. / Title from home page (viewed 04/29/2010). Includes bibliographic references.

A dissertation submitted in fulfilment of the requirements for the degree of Master of Science in Geology to the Faculty of Science, at the University of the Witwatersrand, 2019 / The Palaeoproterozoic Baoulé-Mossi domain of the West African Craton in north-central Ivory Coast is crosscut by a north-northeast trending Ferké Batholith, confined by first-order crustal-scale Ferké Shear Zone (FSZ). To present a geodynamic evolution of the FSZ, incorporation of strato-tectonic, geophysical, geochemical, geochronological revisions is pivotal. In the study region, crosscutting relationship resolved that the oldest unit is formed by gneiss that is uncomfortably overlain by volcano-sedimentary sequences which are intruded by post-basin granitoids, i.e. Ferké Batholith. Volcano-sedimentary sequences consist of conglomeratesandstone-siltstone-mudstone succession and meta-volcaniclastic greywacke unit. Intrusive units making up Ferké Batholith include granodioritic gneiss, granodiorite, granite, tonalite, diorite and pegmatite. U-Pb zircon analysis of samples from the orthogneiss gave a crystallization age of the orthogneiss at 2282 ± 4 Ma, and these were affected by Dext extensional phase around 2132 ± 12 Ma that resulted in basin formation. Fining-upwards volcano-sedimentary sequences were deposited in the extensional-subsiding setting between 2109–2079 Ma. At 2097 Ma, Ferké Batholith emplacement was coeval with the formation of the FSZ. Four main deformational events were recognised crosscutting these rock units. D1 is a progressive deformation event that is dominated by ductile-brittle structures that formed at ~2097 Ma, and is responsible for development of north-northeast trending sinistral shear zones, steeply dipping foliation (S1 and S1-C), sub-horizontal L1 lineation and tight F1 folds. Ferké Batholith emplacement is constrained between 2097 and 1842 Ma U-Pb ages supported by crosscutting relationships. U-Pb age of 2097 Ma constrains D1 and minimum age for deposition of metasedimentary units. Late D1 structures are defined by northwest trending sub-vertical displaced fractures. Northwest trending dilational jogs and sigmoidal en-echelon fractures were formed during late D1. D1 event is related to north-northwest and south-southeast directed principal compressive strain axis. The D2 structures comprise northwest trending F2 folds and foliation (S2) from refolding of D1 structures S1 and F1. Dextral sense of displacement from north-northeast trending shear zones and L2 lineation along the Ferké-Bandama branch developed during D2. West, northwest and west-northwest trending veins (V2) are associated with D2 deformation. Kinematic analysis indicated that the principal compressive strain axis was northnortheast or northeast directed during D2 deformation. iii Brittle fractures, including the northwest to west trending fractures and faults formed the third generation of structure (D3). The traces of D3 structures crosscut those of D1 and D2 features throughout the study area. Northwest sinistral en echelon structures and northeast trending displaced fractures correlate with D3 characteristics i.e. overall north-northeast to northeast maximum shortening direction. Geochemical data show that various granitoids making up the Ferké Batholith are true granites. These intrusive units geochemical character shows calc-alkaline affinities with a very high-K character, mostly I-type and peraluminous composition. Tectonic discrimination diagrams confine the batholith within syn-collision fields. Gold mineralisation associated with FSZ occurs in the metasedimentary units to the southwest (Tortiya region) and northeast (north of Kouloukorosso) of the Ferké Batholith. These regions are structurally controlled and spatially associated with FSZ and hydrothermal veins that formed in response to the regional extensional stress field. The shape of the batholith and/or shear zone sense of displacement permits releasing bends (normal faults) to develop in the regions of Tortiya and Kouloukorosso. / TL (2020)

While the bulk of topography on Earth is generated and maintained by variations in the thickness and density of crust and lithosphere, a significant time-variable contribution is expected as a result of convective flow in the underlying mantle. For over three decades, this dynamic topography has been calculated numerically from inferred density structure and radial viscosity profiles. Resulting models predict ±2 km of long wavelength (i.e., ~ 20,000 km) dynamic topography with minor contributions at wavelengths shorter than ~ 5,000 km. Recently, observational studies have revealed that, at the longest wavelengths, dynamic topography variation is ~ 30% that predicted, with ±1 km amplitudes recovered at shorter wavelengths. Here, the existing database of water-loaded basement depths is streamlined, revised and augmented. By fitting increasingly sophisticated thermal models to a combined database of these oceanic basement depths and corrected heat flow measurements, the average thermal structure of oceanic lithosphere is constrained. Significantly, optimal models are consistent with invariable geochemical and seismological constraints whilst yielding similar values of mantle potential temperature and plate thickness, irrespective of whether heat flow, subsidence or both are fit. After recalculating residual depth anomalies relative to optimal age-depth subsidence and combining them with continental constraints from gravity anomalies, a global spherical harmonic representation is generated. Although, long wavelength dynamic topography increases by ~ 40% in the revised observation-based model, spectral analysis confirms that a fundamental discrepancy between observations and predictions remains. Significantly, residual depth anomalies reveal a ~4,000 km-scale eastward tilt across the Indian Peninsula. This asymmetry extends onshore from the high-elevation Western Ghats in the west to the Krishna-Godavari floodplains in the east. Calibrated inverse modelling of drainage networks suggest that the tilt of the peninsula grew principally in Neogene times with vertical motions linked to asthenospheric temperature anomalies. Uplift rates of up to 0.1 mm a⁻¹ place important constraints on the spatio-temporal evolution of dynamic topography and suggest that rates of transient vertical motion exceed those predicted by many modelling studies. Most numerical models excise the upper ~ 300 km of Earth's mantle and are unable to reconstruct the wavelength and rate of uplift observed across Peninsular India. By contrast, through conversion of upper mantle shear wave velocities to density using a calibrated anelastic parameterisation, it is shown that shorter wavelength (i.e., ≤ 5,000 km) dynamic topography, can mostly be explained by ±150°C asthenospheric temperature anomalies. Inclusion of anelastically corrected density structure in whole-mantle instantaneous flow models also serves to reduce discrepancy between predictions and observations of dynamic topography at long wavelengths. Residual mismatch between observations and predictions is further improved if the basal 300-600 km of large low shear wave velocity regions in the deep mantle are geochemically distinct and negatively buoyant. Finally, inverse modelling of geoid, dynamic topography, gravity and core-mantle boundary topography observations using adapted density structure suggests that geodynamic constraints can be acceptably fit using plausible radial viscosity profiles, contradicting a long-standing assertion that modest long wavelength dynamic topography is incompatible with geoid observations.

The widespread recognition of (ultra)high-pressure ((U)HP) metamorphic rocks in orogens worldwide suggests that subduction and exhumation of crustal rocks from mantle depths are normal processes at convergent plate margins. However, the dynamics of these processes, in particular the comparative roles of erosion and crustal extension, and the driving forces of extension during (U)HP rock exhumation, remain controversial. This thesis presents numerical modeling and field/analytical studies that address the geodynamics of crustal subduction and exhumation in two intensely studied orogens, the Alps and the Caledonides. The 2D numerical models show how different scales and durations of orogeny and plate motions can lead to marked contrasts in the style of orogenic growth, crustal subduction, and (U)HP exhumation. In the Western Alps, rapid exhumation (1-3 cm/a) can be explained by local, syn-orogenic extension driven by the buoyant ascent of deforming (U)HP crust from the subduction channel. Later trans-crustal exhumation probably resulted from the combined effects of syn-convergent thrusting, local extension, and erosion. The low temperatures (500-700°C) of Alpine (U)HP metamorphism are attributable to the small size of the orogen and short duration of subduction/exhumation. Contrary to recent suggestions, neither erosion nor absolute extension is required to explain (U)HP exhumation in the Alps. The Western Gneiss Region (WGR) (Norwegian Caledonides), in contrast, can be explained by subduction to (U)HP conditions followed by plate divergence. Gravitational spreading of a thick, hot orogenic wedge leads to a short period of coeval thrusting and extension. Exhumation of (U)HP crust from the subduction channel is achieved by normal-sense shearing along the top of the (U)HP terrane, with minor associated shortening. Trans-crustal exhumation by vertical thinning of the orogenic wedge results from continued absolute extension and erosion. The comparatively high temperatures (700-800°C) achieved by Caledonian (U)HP rocks reflect the orogen's greater size, slower exhumation rates, and possible stalling of the (U)HP terrane at depth. These contrasting models underscore the variety of possible mechanisms responsible for (U)HP exhumation, and represent new benchmarks in the understanding of Alpine and Caledonian tectonics and (U)HP rock exhumation in general.

This thesis attempts to construct an integrated model for the tectonothermal evolution of the Suru valley region of the High Himalayan Crystalline unit of north-west India, and combines detailed field mapping, petrographic and microstructural analysis, thermobarometric techniques and metamorphic modelling. This work confirms that the metasedimentary lithologies of the Suru valley correspond to the Palaeozoic-Mesozoic Tethyan shelf sediments found in Kashmir and Zanskar and that the meta-igneous bodies correlate with Permian rift-related igneous units. This demonstrates that all the metamorphism in the Suru valley is Himalayan in age. Subsequent to India-Asia collision at ~54 Ma the units of the Suru valley underwent a polyphase deformational and metamorphic history. The large scale structure of the area is that of kilometre-scale, SWvergent recumbent folds that are domed by a later structure, the Suru Dome. Barrovian metamorphism resulting from collision and burial reached a maximum of kyanite grade, and is believed to be syn- to post-kinematic with respect to the formation of the large folds. Thermobarometric analysis indicates that peak conditions relating to this Barrovian event were of the order of 9.5-10.5 kbar and 620-650 ⁰C. A later metamorphic event associated with doming throughout the Zanskar Himalaya and crustal anatexis in the core of the High Himalaya caused re-equilibration of deeper Suru Dome rocks to conditions of 8.7-9.7 kbar and 630-640 ⁰C. Metamorphic modelling, involving phase diagram construction and P-T path determination using Gibbs method calculations, suggests that metamorphic garnets grew under conditions of burial and heating. Rapid exhumation of the High Himalayan Crystallines on the Main Central Thrust and the Zanskar Shear Zone occurred shortly after peak metamorphism. The results suggest that phase diagram construction and P-T path calculation should be used in conjunction in order to confidently model metamorphic rocks.

The Vera Basin is used as a case study to examine the structural evolution and sedimentary response of a basin undergoing uplift and inversion during the Plio-Pleistocene. Particular emphasis is placed on the drainage evolution during that period. Located within the Internal zone of the Betic Cordilleras, the Vera Basin is defined within a large left-lateral shear zone and has evolved as a reponse to isostatic uplift from nappe emplacement during the Oligocene, and by regional compressive tectonics. Since basin formation during the Seravallian, sedimentary fill has been dominantly marine. During the Plio-Pleistocene a switch from marine to continental conditions occurred. These sediments (Cuevas, Espiritu Santo and Salmerbn Formations) represent the final stages of basin fill and form the focus of this study. The Cuevas Formation represents an early Pliocene marine transgression within the Vera Basin. Early sedimentation mulled a pronounced submarine topography produced by a rapid late Miocene fall in sealevel. A broad, shallow shelf platform area existed which opened out to the Pliocene Mediterranean Sea towards the east. Along the northern and western basin margins, wave dominated shorelines were formed. Structural activity was confined to low amounts of basin subsidence and limited left lateral strike-slip movement along the Palomares Fault Zone. The Espiritu Santo Formation marks a major palaeogeographic reorganisation and the final marine phases of the Vera Basin during the mid to late Pliocene. Unsteady strike-slip movement along the Palomares fault zone on the eastern basin margin partially enclosed the Vera Basin by northwards movement of a structurally detached landmass. Gilbert-type fan-delta bodies prograded westwards from the landmass (Sierra Almagrera), infilling the central region of the basin. Early fan-delta sediments were reworked into shoreline areas along the western and northern basin margins. Western margin shorelines retreated northwards as a response to partial enclosure and a gradual lowering of sea-level. Late stages of the Espiritu Santo Formation, saw a fan-delta body prograde from the northern basin margins. Interaction between the basinal and marginal fan-delta bodies enclosed the northern region of the Vera Basin. A swamp/mangrove environment developed within the enclosed northern basin area suggesting a humid, sub-tropical climate. Continental conditions were established during Salmerön Formation times in the late Pliocene. Along the western and northern basin margins, the retreating Pliocene shorelines provided a topography onto which the primary consequent drainage network developed. Three separate drainage systems can be identified on the basis of clast assemblages, palaeocurrents, depositional style and morphological expression. Early deposition was characterised by the progradation of alluvial fans of two drainage systems (Cuevas & Jauro), sourced from the northern and western basin margins. Distal areas of the northern fan system intercalated with an evaporitic playa lake. A third drainage system in the northwest of the basin (Salmerbn) developed within a topographic low between the two fan systems. An increase in structural activity towards the end of the Salmerbn Formation was characterised by a basin wide phase of north-south compression. Uplift and extensional faulting lead to abandonment of the primary drainage network. Fan entrenchment and minor rerouting of sediment supplies marked the establishment of a new secondary consequent drainage network during the Pleistocene. The Pleistocene drainage network records the progressive dissection of the Vera Basin as a response to ongoing regional epeirogenic uplift. During this post-inversion phase the Rios Antas, Almanzora and Aguas developed respectively along the western, northern and southern basin margins as- a series of braided streams. Distal, coastal areas of this drainage network are recorded by a series of Pleistocene shoreline sequences which developed as a response to fluctuating sea-level during the Pleistocene glacial and interglacial periods. Early Pleistocene proximal parts of the drainage network are well preserved. Distal parts of the Pleistocene fluvial system display limited evidence for interaction between the drainage network and shoreline sequences. This lack of preservation relates to the high energy, wave dominated depositional setting of the Pleistocene shoreline areas which reworked fluvial sediment inputs into the shoreline environment. The Plio-Pleistocene evolution of the Vera Basin, and in particular the development of the fluvial during system this period has been highly complex. Despite the importance of sea-level and climatic controls, tectonic activity during this period of basin inversion has been the dominant control on the positioning of the drainage networks, depositional styles and sediment supply.

Thesis (M.S.)--Ohio State University, 2008. / Title from first page of PDF file. Includes bibliographical references (p. 38-43).

Thesis (Ph.D.)--University of Wyoming, 2007. / Title from PDF title page (viewed on July 26, 2010). Includes bibliographical references.

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