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Stypula, Merril J.

Geology

2012

M.S.

The East Gobi Fault Zone (EGFZ) is a NE-striking structural corridor located in southeastern Mongolia that records a complex, polyphase history of Mesozoic-Cenozoic intracontinental deformation. The lithologies within and adjacent to the EGFZ record the geologic history of the amalgamation of Asia, and have been mapped as Precambrian in age. Recent studies along the EGFZ have found these lithologies are in many instances Mesozoic tectonites and Paleozoic volcanic and sedimentary protoliths, and comprise a vast Late Triassic sinistral shear zone. The primary focus of this study is to reveal new age data from migmatite, mylonite and pegmatite units sampled at Tavan Har, southeast Mongolia, via V-Pb zircon geochronology in order to better constrain the timing of partial melting and associated high-grade metamorphism documented throughout this region.
²⁰⁶Pb/²³⁸U apparent ages obtained from an in situ analysis of zircon grains separated from these units indicate at least five tectonic events responsible for zircon crystallization and/or modification, generally resulting from the presence ofa metamorphically derived fluid or a partial melt. U-Pb zircon age data is combined with microstructural analyses, cathodoluminescence and backscattered images, and a detailed evaluation of individual zircon textures as a means to better understand and constrain the tectonic history of southeastern Mongolia. Through correlation of age data and the deformation history at Tavan Har with the history of collisional orogenesis and plate boundary evolution in Asia, this study contributes to our understanding of the processes that govern continental deformation as well as the role of structural inheritance.