Doctor of Philosophy (PhD)
Geology and Geophysics
This dissertation focuses on the kinematic evolution of contractional tectonics: the Himalayan fold-thrust belt along the collisional orogenic belts, and growth of the basement-cored monoclines in Colorado Plateau. Ongoing Himalayan growth is generally thought to be dominated by duplexing and/or extrusion processes. Duplexing models highlight accretion of material from the subducting plate to the over-riding orogenic wedge, whereas extrusion models focus on up-dip translation of a block bounded by out-of-sequence faults. Here, a primary outstanding question involves the uncertain relationship of the Berinag thrust and the Tons thrust, structures with displacements of >80 km and >40 km, respectively. The uncertainty allows the complete range of duplexing and extrusion processes for the integrated kinematic history since the Middle Miocene. To address this issue, field mapping, kinematic analysis, and analysis of quartz recrystallization textures were performed. Our results reveal a new discovery: a ~ 450 m thick top-to-southwest shear zone, termed the Pabbar thrust. The Pabbar thrust placed the Outer Lesser Himalayan Sequence (the Tons thrust hanging wall) directly on the Berinag Group (the Berinag thrust hanging wall). This discovery requires that the Pabbar thrust developed first, followed by footwall accretion of the Berinag-Tons thrust sheet, operating as a single structure. The Berinag thrust and Tons thrust are in fact the same structure. Low temperature thermochronological data, and a line-length balanced palinspastic reconstruction across the NW Indian Himalaya place robust constraint on Himalayan mountain building process: (1) Late Oligocene–Middle Miocene emplacement of the Great Himalayan Crystalline Complex (GHC) and juxtaposing of the THS atop the Lesser Himalayan Sequence (LHS). (2) Middle–Late Miocene accretion of the Berinag-Tons thrust sheet; and (3) subsequent growth via a hinterland-dipping upper crustal duplexing and an antiformal stack of mid-crustal horses developed simultaneously. Trishear provides an alternative model of fault-propagation. It is successfully applied to create balanced cross sections for the monoclines in Uncompahgre Uplift. Forward modeling of strains around the fault tip zone demonstrates excellent agreement with field-based strain calculated from deformation bands, and can explain distribution and orientation of deformation bands in eolian sandstone.
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Yu, Hongjiao, "Contractional Tectonics: Investigations of Ongoing Construction of the Himalaya Fold-thrust Belt and the Trishear Model of Fault-propagation Folding" (2014). LSU Doctoral Dissertations. 2683.
Webb, A. Alexander