Stratigraphic signatures of convergent orogenesis from the plate interior : studies from Tibet and the southern Rocky Mountains




Bush, Meredith Anne

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Fundamental questions remain in geology regarding the growth and development of the continental landscape. The existence of major mountain belts and high plateaus in the plate interior, over a thousand kilometers from a plate boundary, requires a complex combination of tectonic and climatic pre-conditions combined with inherited structures, active tectonics, geodynamic processes, and climatic feedback. Through these studies of the basin records of orogenesis in the Qaidam basin of northern Tibet and the southern Rocky Mountain basins of North America, we provide new constraints on the timing of deformation, the development of proximal basins, and the evolution of continental-scale drainage patterns in two of the most prominent modern mountain belts. Three studies are presented in this dissertation, each investigating a different aspect of continental plate-interior basin development. In Chapter 2, the Cenozoic sedimentary record from the Qaidam basin is investigated through a sedimentological and multi-proxy provenance study. Provenance and stratigraphic analysis reveals syn-collisional exhumation of the Eastern Kunlun Shan and Qilian Shan, marking the early establishment of the borders of the Tibetan plateau. Chapter 3 investigates the record of easternmost Laramide deformation in the southern Rocky Mountains. Detrital zircon U-Pb geochronology of Cretaceous through Eocene sedimentary units in the Raton basin provides new constraints on the uplift and exhumation of the Sangre de Cristo range, revealing initial exhumation of Laramide basement material in the Campanian, the formation of a drainage divide within the Sangre de Cristo range by the Paleocene, and continued exhumation through the Eocene. The final study (Chapter 4) looks at regional patterns of uplift, exhumation, and drainage reorganization during the latest Cretaceous through Eocene in the southern Rocky Mountains. Initial Laramide-style deformation introduced basement material into the basins while maintaining integrated basins, while continued exhumation throughout the Paleogene resulted in partitioning of basins into more localized depocenters. Provenance analysis of strata from the San Juan, Galisteo-El Rito, and Raton basins reveals new depositional ages, as well as patterns of basin filling and drainage integration during Laramide thrusting, pluton emplacement in the San Juan mountains, and the transition to south-directed continental drainage systems that terminate in the Gulf of Mexico. Together, these studies provide a framework for understanding the co-evolution of sedimentary basins and mountain belts in the plate interior based on the recognition of initial deformation, continued exhumation and drainage integration, and partitioning of basins due to the formation of topographic barriers.


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