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Abstract

The Tibetan Plateau is the greatest concentration of continental crust on Earth, and intimately linked to the quintessential example of continent-continent collision: India and Eurasia. The overarching goal of this thesis is to investigate the distribution of exceptionally thick continental crust and high altitude surfaces from the latest Cretaceous—just prior to,onset of collision—to modern day in order to better understand how Earth accommodates continental crustal mass during continental collisions. This goal is achieved by employing stable isotope paleoaltimetry methodology to four Cenozoic sedimentary basins: three just north of the Indus Yarlung Suture within the Linzizhong arc, and one near the boundary of the Lhasa and Qiangtang tectonic blocks. Carbonate `clumped'-isotope paleothermometry substantially improves traditional stable isotope paleoaltimetry techniques by providing critical constraints on carbonate formation temperature, and thus, the isotopic composition of ancient meteoric water. The paleoelevation reconstructions presented in this work reflect the existence of an Andean-type high elevation Linzizhong arc just prior to the onset of collision, and the maintenance of a high altitude land surface throughout the Cenozoic. The northern margin of the Lhasa block has been high since at least the Oligocene, but quite likely much earlier. These paleoelevation reconstructions together require revision of past tectonic models arguing for a Miocene to Pliocene rapid uplift of the southern Tibetan Plateau, and the,paleoclimate and tectonic implications these long-standing models invoke.,Mass balance of the continental crust within the India-Asia domain has been debated for more than thirty years. In this work, I revisit mass balance calculations using our new knowledge of a thick Linzizhong arc prior to onset of collision, and the most up-to-date constraints on paleogeography, plate kinematics, and the age of collision onset. The mass balance calculations yield a 50% loss of continental crust from within the collisional domain boundaries at the Earth's surface. We suggest that subduction of continental crust into the mantle beneath Eurasia has been equally important as crustal thickening in accommodating continental mass during India-Asia collision.,Paleoclimatology and paleoaltimetry employ the carbonate oxygen stable isotope record to reconstruct the composition of ancient meteoric water. As such, these techniques require the retention of primary isotopic compositions within authigenic minerals through variably complex thermal histories. The objective of the last section of this work is to identify the effects of shallow-to-deep burial and exhumation|thermal conditions common to areas of geologic interest and exposed strata|on carbonate 18O and 47 compositions. I use isotopic, geochemical, and optical techniques to identify cryptic recrystallization within marine carbonate that has been pervasively altered in oxygen isotope space but appear otherwise texturally pristine. I propose future work to strengthen our understanding of the eects of cryptic carbonate diagenesis on marine and terrestrial carbonates and to increase our ability to recognize the diagenetic ngerprint of cryptic alteration. Our ability to screen for such cryptic diagenesis is critical for the future use of the carbonate proxy record in geological applications. However, the possibility remains that we may not be able to place sufficient constraints on the thermal and diagenetic histories of terrestrial carbonates to robustly use their stable isotopic values for paleoclimatology and tectonics.

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