Crustal thickness and paleo-elevation in SE Tibet during the Eocene-Oligocene: Insights from whole-rock La/Yb ratios.

The topographic evolution of SE Tibet is essential for understanding the growth of this orogenic plateau margin and the mechanism of continental deformation in general. Stable isotopes have been used to construct the paleo-elevation of SE Tibet during the Cenozoic. However, this methodology's reliability for the region is controversial; the results require validation through other independent constraints. The Eocene-Oligocene adakite-like rocks exposed along the Jinshajiang Suture are mostly the production of melts from the lower crust, and thus their geochemical features are used to track ancient crustal thickness and plateau elevation of SE Tibet. The whole-rock [La/Yb] N ratios indicate a thickened SE Tibet. Meanwhile, the paleo-elevation based on the calculated crustal thickness shows that central and southeastern Tibet had reached modern heights by the early Oligocene, corroborating results by stable isotope paleoaltimetry. Synthesizing previous studies and our results, we suppose that the deformation caused by the India-Aisa collision had propagated to and thickened central and southeastern Tibet before the Eocene-Oligocene. The uplifted and low-gradient plateau margin of SE Tibet had already been formed by this time. The lateral extrusion has mainly accommodated the deformation with minor shortening since the late Eocene. • Eocene-Oligocene adakite-like rocks exposed in SE Tibet were derived from melts in the deep crust. • Whole-rock La/Yb ratio-derived Moho depth indicates a thickened SE Tibet during the late Eocene-early Oligocene. • The paleo-elevation of SE Tibet had reached modern heights before the early Oligocene. [ABSTRACT FROM AUTHOR]