The Cretaceous-Tertiary tectonic evolution of the Lhasa Terrane, Tibet

A thorough understanding of Tibetan Plateau growth requires knowledge of the geological evolution of the Tibetan terranes as they were accreted to the Eurasian margin during the Phanerozoic. This dissertation research addresses the tectonic evolution of the southernmost of these, the Lhasa terrane of Tibet from the Late Jurassic to Eocene. The data and insights presented herein are the result of extensive geologic fieldwork in the northern and central Lhasa terrane of Tibet. In this work I present new geologic mapping and thermochronologic data that reveals a terrane scale passive roof thrust belt in the northern Lhasa terrane that accommodates significant upper crustal shortening without exhuming basement rocks. Through the development of a geospatially referenced database of igneous crystallization ages, I show that Cretaceous magmatism on the Lhasa terrane was not static, but exhibited significant temporal-spatial migrations. I interpret these movements as the result of variations in Neo-Tethyan slab dip and suggest that these variations are a major factor in shaping the Cretaceous tectonics of the Lhasa terrane. Finally, I present the Cretaceous-Eocene tectonic evolution of the Lhasa terrane that shows that the Lhasa terrane was above sea level and likely had attained significant elevation prior to the accretion of India to Eurasia and that the development of the high elevation Plateau developed outward from a central core, rather than from south to north as is commonly thought. These insights refute the widely held view that the Tibetan Plateau is the result of the Cenozoic Indo-Asian collision.