Thesis (Ph. D.)--University of Texas at Austin, 2003. / Vita. Includes bibliographical references. Available also from UMI Company.

Thesis (Ph. D.)--University of Texas at Austin, 2003. / Available also in an electronic version.

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Extensive new trackline coverage of the Chile Trench between 23°S and 34°S, including more than 60 bathymetric and seismic reflection profiles across the trench axis, allows a much more detailed study of the tectonics and sedimentation of this feature than previously possible. Sediment distribution along the axis shows a remarkable variation from over a kilometer of turbidites in the axis south of 33°S to a barren axis in places north of 27°S. Turbidity currents originating on the outer continental margin in the south carry sediment northward along the axis. Ponding behind structural barriers created by plate convergence restricts the amount of sediment reaching northern trench sections. Horst and graben blocks are the dominant structural features on the seaward trench slope, with fault offsets of 500 to 1000 meters. Grabens range in width from 4 to 8 km, while the faulting probably extends down into oceanic layer three. Faulting is most pronounced in the deeper northern parts of the trench, but can also be seen in the basement beneath undeformed axial sediments in the south. This crustal rupture can be related to extensional stress in the upper oceanic crust due to the downbending of the Nazca Plate prior to subduction. Most of the active normal faulting occurs soon after the plate begins its descent into the trench, and not within the trench axis. Using structure, sediment distribution, bathymetry, and morphology, the trench and outer continental margin can be divided into three provinces (Northern, 23°-27°S; Central 27°-33°S; and Southern, 33°-34°S) separated by distinct tectonic transition zones at 27°S and 33°S. These boundaries coincide with breaks in onshore geologic trends and correlate less well with seismic zone segmentation. An analysis of potential strain due to subduction along a non-arcuate trench concludes that segmentation in the trench is probably controlled more by continental block structure than by the linearity of the trench. A narrow, continuous pond of sediment partially fills the Central Province trench axis between 32°30'S and 27°S. Trench axis morphology and piston core samples indicate there is transport of terrigenous sediment down the axis from the abundant sediment supply regions of the Southern Province. A model is formulated from this data which accounts for the sediment wedge in the Central Province by supply of turbidites from the south. A steady-state of axial fill can be maintained by one typical flow every 14 to 27 years. Uplifted axial turbidites are present on the seaward trench slope at 30°35'S, elevated 350 meters above the axis. Radiocarbon dating puts the age of initial uplift at 5380 ± 350 years B.P., which results in a minimum vertical movement rate of 6.5 cm/yr. Reversed faulting due to compressive stresses generated by plate convergence is the presumed mechanism of uplift. A model is proposed to explain the differences in the Chilean continental margin morphology in each of the three provinces. The radical differences in the amount of sediment available to the trench axis appears to be a prime influence in the development of the margin. An abundance of axial sediments provides a buffer zone along the major interplate contact (slip) zone, plus material to be accreted into the lower continental slope. If the amount of axial sediments is limited, excessive frictional resistance to slippage between the converging plates may tectonically erode the margin by slowly wearing away the underside of the continental slope. / Graduation date: 1976

In the Ordovician-Silurian Caledonian orogenic belt of northern Scotland, two major thrust nappes, the Moine and Naver nappes, contain a series of granitic plutons. The Rogart, Strath Halladale and Helmsdale granites have been studied using field and microstructural fabric analysis. Their emplacement mechanisms and pre, syn or post-tectonic status with respect to phases of Caledonian ductile deformation have been detailed. The petrogenesis of the Strath Halladale and Helmsdale granites has been examined within the framework of a regional geochemical study involving nine Caledonian high Ba-Sr granitoids. The foliated Strath Halladale Granite comprises a series of easterly-dipping sheets that were intruded into structurally high parts of the Naver Nappe in northeastern Sutherland. The granite contains magmatic-state shear zones that consistently show top-to-the- W-to- NW sense of movement; it was emplaced during Caledonian (02) west-directed thrusting. The Rogart Granite was emplaced into the footwall of the Naver Thrust in southeastern Sutherland. It comprises early, sheeted quartz diorites that carry magmatic to solid-state fabrics formed by thrust-related, west-directed ductile deformation and a central igneous quartz monzodiorite-granodiorite-granite complex that ballooned into a tectonically created void formed along the Strath Fleet Lineament after D2 thrusting. The emplacement of the Rogart Granite encompassed the switchover from west-directed thrusting to strike-slip tectonics in this area. The Helmsdale Granite was emplaced into the highest parts of the Naver Nappe in eastern Sutherland. It does not contain any emplacement-related or tectonically-induced fabrics and is post-tectonic with respect to Caledonian deformation. Its emplacement mechanism and hence the Caledonian significance of the adjacent Helmsdale Fault remain speculative. Geochemistry confirms that the Strath Halladale and Helmsdale granites are part of the Caledonian high Ba-Sr granites (sensu Tarney & Jones 1994) and indicates melt evolution by assimilation fractional crystallization (AFC) involving Moine metasediment. Associated mafic rocks do not form parents to the granites but represent a variety of genetically-related cumulates. Nine Caledonian high Ba-Sr plutons in northern Scotland show a systematic isotopic variability. Plutons with the highest 87Sr/86Sr(i)have the lowest ENd(i) and the highest 8180, whereas plutons with lower 87Sr/86Sr(i)have complementary higher ENd(i) and lower 8180. Syenite-dominated complexes evolved by assimilation fractional crystallization (AFC) involving depleted granulite-facies basement whereas the granites assimilated Moine metasediment. Combining available age data with the observed isotope systematics suggests, that the syenites recorded progressive (source) enrichment over c. 30 Ma followed by a short-lived, isotopically-diverse, magmatic pulse at c. 425 Ma.

Thesis (M.S.) in Earth Sciences--University of Maine, 2007. / Includes vita. Includes bibliographical references (leaves 138-145).

Thesis (M.S.)--Oregon State University, 1997. / Typescript (photocopy). Includes bibliographical references (leaves 47-51). Also available on the World Wide Web.

Thesis--University of Wisconsin--Madison. / Typescript. Vita. Description based on print version record. Includes bibliographical references (leaves 575-599).