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Geology Club Seminar

Thursday, March 28, 2019
4:00pm to 5:00pm
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Arms 151 (Buwalda Room)
Isotopic and geochemical tracers of crustal thickness in southern Tibetan granites
Ellen Alexander, Graduate Student, Department of Earth, Planetary, and Space Sciences, UCLA,

In southern Tibet, voluminous granitoids of the Gangdese batholith emplaced between ~200 Ma to 20 Ma provide a spatiotemporal window into the geochemical and tectonic evolution of the crust throughout the India-Asia collision. Indirect geochemical proxies for estimating crustal thickness have recently become popularized as a method for reconstructing the crustal evolution of the Tibetan Plateau throughout collision. In this talk I evaluate the validity of isotopic and geochemical tracers for crustal thickness, and present new data for a suite of granitoids along a N-S transect near Lhasa, Tibet. Hf and O isotope geochemistry of whole rocks and constituent zircons together with whole-rock chemistry reveal a coherent magmatic history of Gangdese granitoids. I compare zircon and whole-rock εHf data with previous Nd-based thermoisotopic models, which indicate that the Lhasa block maintained a wedge-shaped crustal geometry from the early Jurassic until the onset of collision. I will also present preliminary findings of coupled quartz and zircon Ti thermobarometry.