Thesis (Ph. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references.

No description available.

Lithospheric-scale geodynamic processes are interconnected with surface processes such as erosion and tectonic denudation, therefore the integration of geological and geophysical data is valuable when developing geodynamic models. One geodynamic problem that has gained worldwide interest is the contrast in lithospheric properties between the hot and thin Canadian Cordillera and cold and thick North American craton. This thesis focuses on characterizing two aspects of the crust in western Canada: 1) ancient surface and near-surface processes using low-temperature (U-Th)/He thermochronology; and 2) modern geothermal gradients using a wavelet analysis of magnetic anomalies. The first study resolves a differential, tectonically-driven Cretaceous exhumation history in the northern Canadian Cordillera. The second study finds that Curie depths (~580 °C) are shallow throughout the Cordillera, averaging ~15 km, compared to the Canadian Shield, averaging ~33 km. Both studies provide useful constraints for modeling the geodynamic evolution of the Canadian Cordillera.

An imbricated Mesozoic to Palaeogene continental margin sequence is juxtaposed with ophiolitic rocks in the East Arm of Sulawesi, Indonesia. The two tectonic terranes are bounded by the Batui Thrust and Balantak Fault System, which are considered to be the surface expression of the collision zone between the Banggai-Sula Platform and the Eastern Sulawesi Ophiolite Belt. The collision complex contains three distinctive sedimentary sequences : 1) Triassic-Palaeogene continental margin sediments, ii) Cretaceous pelagic sediments and iii) Neogene coarse clastic sediments and volcanogenic turbidites. (i) Late Triassic Lemo Beds consisting largely of carbonate-slope deposits and subsidiary clastics including quartz-rich lithic sandstones and lensoidal pebbly mudstone and conglomeratic breccia. The hemipelagic limestones are rich in micro-fossils. Some beds of the limestone contain bivalves and ammonites, including Misolia, which typifies the Triassic-Jurassic sequence of eastern Indonesia. The Jurassic Kapali Beds are dominated by quartzose arenites containing significant amounts of plant remains and lumps of coal. The Late Jurassic sediments consist of neritic carbonate deposits (Nambo Beds and Sinsidik Beds) containing ammonites and belemnites, including Belemnopsis uhligi Stevens, of Late Jurassic age. The Jurassic sediments are overlain unconformably by Late Cretaceous Luok Beds which are predominantly calcilutite with chert nodules rich in microfossils. The Luok Beds are unconformably overlain by the Palaeogene Salodik Limestones which consist of carbonate platform sediments rich in both benthic and planktonic foraminifera of Eocene to Early Miocene age. These sediments were deposited on the continental margin of the Banggai-Sula Platform. (ii) Deep-sea sediments (Boba Beds) consist largely of chert and subsidiary calcilutite rich in radiolaria of Cretaceous age. These rocks are part of an ophiolite suite. (iii) Coarse clastic sediments (Kolo Beds and Biak Conglomerates) are typical post-orogenic clastic rocks deposited on top of the collision complex. They are composed of material derived from both the continental margin sequence and ophiolite suite. Volcanogenic Lonsuit Turbidites occur in the northern part of the East Arm in Poh Head and unconformably overlie the ophiolite suite. Late Miocene to Pliocene planktonic foraminifera occur in the intercalated marlstone and marly sandstone beds within these rocks. The collision zone is marked by the occurrence of Kolokolo Melange, which contain exotic fragments detached from both the ophiolite suite and the continental margin sequence and a matrix of calcareous mudstone and marlstone rich in planktonic foraminifera of late Middle Miocene to Pliocene age. The melange is believed to have been formed during and after the collision of the Banggai-Sula Platform with the Eastern Sulawesi Ophiolite Belt. Hence, the collision event took place in Middle Miocene time. The occurrence of at least three terraces of Quaternary coraline reefs on the south coast of the East Arm of Sulawesi testifies to the rapid uplift of the region. Seismic data suggest that the collision might still be in progress at the present time.

Masters of Science / 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.

Convergent continental margins are regions of intense deformation caused by the interaction of oceanic plates with continents. The spatial extent of deformation is broadly commensurate with the specific time scale of the causative phenomenon. For example, subduction-related short-term deformation is limited to <200 km from the margin, whereas long-term plate convergence cause deformation over ∼1000 km landward. Deformation is thus manifested in multiple ways, with attributes depending on the scale of measurement. In this thesis we investigate the use of two geophysical approaches in the study of deformation: 1) The analysis of potential-field anomalies to derive estimates of the elastic thickness (Te) of the lithosphere, and 2) The structural study of past and present subduction systems using seismic observations and modelling. Both approaches involve the development of appropriate methodologies for data analysis and modelling, and their application to the western Canadian landmass. Our findings are summarized as follows: 1) We develop a wavelet-based technique to map variations in Te and its anisotropy; 2) We show how a step-wise transition in Te and its anisotropy from the Cordillera to the Craton is a major factor influencing lithospheric deformation; 3) We implement a waveform modelling tool that includes the effects of structural heterogeneity and anisotropy for teleseismic applications, and use it to model the signature of a fossil subduction zone in a Paleoproterozoic terrane; 4) We use teleseismic recordings to map slab edge morphology in northern Cascadia and show how slab window tectonism and slab stretching led to the creation of the oceanic Explorer plate; 5) We use seismic signals from the subducting oceanic crust to calculate elevated Poisson’s ratio and infer high pore-fluid pressures and a low-permeability plate boundary within the forearc region of northern Cascadia. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

The heterogeneity of the continental crust has a first order control on the dynamics of plate tectonic processes and the compositions of the Earth in both time and space. Heterogeneity can be characterized at a variety of scales and in a multitude of tectonic environments, but it is the links between seemingly disparate tectonic settings and crustal levels that are critical in understanding construction of the continents. The focus of this dissertation work is to apply microtextural, microgeochemical, whole rock geochemical and traditional petrographic techniques to study features in both deep and shallow crustal igneous rocks. The goal of these efforts is to better understand the roles that magmatic processes, mafic-felsic magma interaction, and partial melting have on the evolution of continental crust. Two principal field areas were selected, the Gouldsboro pluton in coastal Maine and the Fehr granite in northern Saskatchewan, Canada, because they each represent end-members of the processes involved with the generation, modification, transport, and emplacement of magmas that build continental crust. Evidence for bimodal magmatism preserved in the Silurian age Gouldsboro pluton has led to a refined model for the construction of shallow crustal magma chambers. Research efforts focused on the Neoarchean Fehr granite and Paleoproterozoic Chipman dike swarm have contributed to the current understanding of the links between high temperature metamorphism (migmitization) and the production of new felsic magmas as well as the rheological and chemical influences of mafic-felsic magma interaction in the deep crust. The results of these combined field and laboratory efforts have demonstrated the important role of mafic-felsic magma interaction on the strength and composition of both deep and shallow continental crust and have contributed to the current understanding of the complex links between deep crustal heterogeneity and bimodal magmatism at shallow crustal levels.

Panamá arc activity has been divided into three episodes, the Late Cretaceous to Eocene episode, the Miocene episode, and the Pliocene to recent adakite suite. Rocks from the oldest episode are dominantly hornblende bearing, contain a large negative Nb-Ta anomaly, and exhibit enrichment of large-ion lithophile elements (LILEs). These characteristics are all indicators that the Late Cretaceous-Eocene episode rocks formed from a hydrous mantle wedge derived subduction zone magma. Miocene episode rocks are commonly calc-alkaline throughout Panamá. In contrast, Miocene episode rocks from the Panamá Canal (PC) are strongly tholeiitic, lack hydrous minerals, have a decreased Nb-Ta subduction zone signal, and exhibit LILE depletion relative to older PC volcanism as well as the older Panamá arc episodes. New major element, trace element, and radiogenic isotope data has been analyzed for rocks from the Western Canal Basin (WCB) between El Valle volcano and the PC. The rocks contain both calc-alkaline and tholeiitic signatures, and range from basalt to dacite in composition. In terms of trace elements, the rocks exhibit enriched heavy rare earth element concentrations that are among the highest in all of Panamá. The Ba/Yb values for WCB samples are between the depleted PC samples and fluid rich El Valle samples. The WCB Ta/Yb values are similar to PC samples, with both exhibiting a lesser subduction zone signal than the Cretaceous-Eocene arc. On a V versus Ti tectonic discrimination diagram both PC and WCB samples plot in the MORB/BAB/CFB field. Pb and Sr isotope ratios for the Panamá Canal Basin rocks are similar to the Cordilleran arc, whereas Hf and Nd isotope ratios are the highest measured in all of Panamá and are consistent with the contribution of young asthenospheric mantle. Overall, trace element, isotopic and geophysical data indicate that the western Canal basin volcanic rocks formed due to the influx of young juvenile mantle in an extensional tectonic system. One explanation is the existence of an underlying tear in the subducted slab due to the ongoing collision of Panamá and South America. This is consistent with the fracturing of the Isthmus as proposed by Farris et al. (2011), and a tear in the underlying slab would allow for the influx of young mantle material. To place constraints on the crustal structure of the Canal basin, a series of gravity measurements were conducted. Bouguer gravity models exhibit a series of westward deepening half-grabens filled with low-density volcano-sedimentary material. Such horst and graben systems are interpreted to have formed due to extension in both east-west and north-south directions. Sub-orthogonal normal fault systems reflect the extensional nature of the Panamá Canal Basin. The models also indicate that 3 to 5 km thick volcano-sedimentary basins dominate the shallow subsurface, indicating that observed lavas are likely low in volume. Finally, the gravity models show the existence of a continuous sedimentary basin across the isthmus, which allows for the existence of a narrow strait connecting the Caribbean and Pacific during this time as proposed by Collins et al. (1996). / A Thesis submitted to the Department of Earth, Ocean, and Atmospheric Sciences in partial fulfillment of the requirements for the degree of Master of Science. / Fall Semester 2015. / December 7, 2015. / Arc Geochemistry, Bouguer Anomalies, Caribbean Tectonics, El Valle, Isotope Geochemistry, Panama Canal / Includes bibliographical references. / David W. Farris, Professor Directing Thesis; A. Leroy Odom, Committee Member; Vincent J. M. Salters, Committee Member.

Material and structure, being indivisible, provide the basis for this thesis exploration. The material of choice was concrete, inspired by the use of cast objects made in the studio. Through the act of form making and casting tectonic material integration developed. Intrinsic structural qualities of the material were affirmed with repeated drawing, form making and casting, while exploring the phenomenon of the transferred surface. An open urban site in Washington, DC was chosen before a building type was determined. Neighborhood and site analysis identified the potential need for a Firehouse. This building type allowed the opportunity to explore the use of concrete for vehicles as well as people. Can concrete, maligned for being cold and harsh, hold a building and its uses in comfort and beauty? / Master of Architecture / I struggled to find a direction for my Master of Architecture Thesis, like most, but knew materiality and tectonics would be the focus. After being enthralled with the annual WAAC Concrete competition, and the rampant use of ROCKITE in the Old Town studio I settled on formed concrete as a driver. An urban site was a given, an empty lot at 14th Street and V Street NW that seemed a managable size was perfect. Neigborhood and site analysis revealed the potential need for a Firehouse, in the pull-through style popularized by suburban stations.(1) This building type allowed many opportunities to explore concrete structural tectonics, for the human user and the automobile. Ideas of how concrete holds different materials, and how those relationships create a comfortable and useful space were examined in drawing and model.

No description available.