Browsing by Subject "tectonics"
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Item Evolution of the Galapagos Rise and the Bauer Microplate: implications for the Nazca plate(Texas A&M University, 2006-04-12) Wright, Jennifer Catherine McGuireAnalysis of the satellite altimetry based predicted bathymetry, magnetic anomalies, and earthquake seismic data relating to the geophysical structure on the Nazca plate indicates that the Galapagos Rise system served as the transitional spreading system between Pacific-Farallon spreading and the current East Pacific Rise (EPR) system. First order age/depth relationships for this area indicate that the Galapagos Rise, the most prominent extinct spreading system within the Nazca plate, accommodated most of the Pacific-Nazca plate separation from ~23 million years ago (Ma) to ~8 Ma. After this time, spreading was dominantly along the EPR, with probable ultra slow spreading along the Galapagos Rise continuing until very recent times (0-5 Ma). Magnetic lineations and depth trends across the Bauer Basin suggest that it was captured between the failing Galapagos Rise and the currently active EPR. Anomalously shallow ridge crests along the Galapagos Rise indicate that magmatic activity may have occurred until very recent time (0-5 Ma). Tightly curved (concave southward) fracture zones offsetting Galapagos Rise ridge segments indicate a pole of rotation at the present day position of ~22.5 S and ~99.5 W. The curvature of the fracture zones and the fan-shaped spreading pattern of seafloor structures produced at the Galapagos Rise indicate that the Galapagos Rise initiated parallel to the Menda??a fracture zone. Consistent with the rotation of the Nazca plate after the fragmentation of the Farallon plate, the Galapagos Rise rotated counterclockwise during its active phase. The Galapagos Rise initiated in the vicinity of Gallego fracture zones and propagated southward. Failure of the Galapagos Rise occurred as spreading jumped westward in stages to the East Pacific Rise.Item Motion and evolution of the Chaochou Fault, Southern Taiwan(Texas A&M University, 2005-11-01) Hassler, Lauren E.The Chaochou Fault (CCF) is both an important lithologic boundary and a significant topographic feature in the Taiwan orogenic belt. It is the geologic boundary between the Slate Belt to the east, and the Western Foothills to the west. Although the fault is known to be a high angle oblique sinistral thrust fault in places, both its kinematic history and its current role in the development of the orogen are poorly understood. Field fabric data suggest that structural orientations vary along strike, particularly in the middle segment, the suspected location of the intersection of the on-land Eurasian continent-ocean boundary and the Luzon Island Arc. Foliation/solution cleavage is oriented NE-SW and in the northern and southern sections, but ESE-WNW in the middle segment. Slip lineations also reveal a change in fault motion from dip-parallel in the north to a more scattered pattern in the south. This correlates somewhat with recent GPS results, which indicate that the direction of current horizontal surface motion changes along strike from nearly perpendicular to the fault in the northern field area, to oblique and nearly parallel to the fault in the southern field area. The magnitude of vertical surface motion vectors, relative to Lanyu Island, decreases to the south. Surface morphology parameters, including mountain front sinuosity and valley floor width/valley height ratio indicate higher activity and uplift in the north. These observations correlate well with published apatite/zircon fission track data that indicate un-reset ages in the south, and reset ages in the northern segment. Geodetic and geomorphic data indicate that the northern segment of the CCF and Slate Belt are currently undergoing rapid uplift related to oblique arc-continent collision between the Eurasian continent and the Luzon arc. The southern segment is significantly less active perhaps because the orogen is not yet involved in direct arc-continent collision.Item Thermal and Structural Constraints on the Tectonic Evolution of the Idaho-Wyoming-Utah Thrust Belt(2013-08-09) Chapman, Shay MichaelThe timing of motion on thrust faults in the Idaho-Wyoming-Utah (IWU) thrust belt comes from synorogenic sediments, apatite thermochronology and direct dating of fault rocks coupled with good geometrical constraints of the subsurface structure. The thermal history comes from the analyses of apatite thermochronology, thermal maturation of hydrocarbon source rocks and isotope analysis of fluid inclusions from syntectonic veins. New information from zircon fission track and zircon (U-Th)/He analysis provide constraints on the thermal evolution of the IWU thrust belt over geological time. These analyses demonstrate that the time-temperature pathway of the rocks sampled never reached the required conditions to reset the thermochronometers necessary to provide new timing constraints. Previous thermal constraints for maximum temperatures of IWU thrust belt rocks, place the lower limit at ~110?C and the upper limit at ~328?C. New zircon fission track results suggest an upper limit at ~180?C for million year time scales. ID-TIMS and LA-ICPMS of syntectonic calcite veins suggest that new techniques for dating times of active deformation are viable given that radiogenic isotope concentrations occur at sufficient levels within the vein material.