Paleogene tectonic deformation on the eastern Tibetan Plateau: Evidence from sedimentary sequences and apatite fission track thermochronology in the Nangqian Basin

The tectonic deformation and topographic growth processes of the eastern Tibetan Plateau provide clues for deciphering the geologic history of the Himalaya-Tibet orogenic plateau. The Nangqian Basin is a typical representative of the Paleogene basin group across the eastern Tibetan Plateau. The sedimentary sequences in this basin archive the deformation and growth of the eastern Tibetan Plateau. We investigated and measured the strata sequences of the Paleogene sediments in the Nangqian Basin, and conducted apatite fission track (AFT) analyses within these sediments. The results show three phases of coarse clastic deposition in the basin in the Paleocene, early Eocene, and early Oligocene, indicating simultaneous regional deformation. The detrital AFT ages suggest rapid exhumation of the sedimentary provenance from 52 to 45 Ma. Together with published re-sults, we recognize four major tectonic activities in the Nangqian region during the Paleogene. During the Paleocene, localized crustal deformation was occurred by thrusting immediately in response to the initial collision between the Indian and Asian plates; during the Eocene (52-45 Ma and 41-35 Ma), intense mountain exhumation occurred, making the region attain a certain height (similar to 3 km) because of the reactivated subduction of the Jinsha suture; and during the early Oligocene, tectonic deformation probably caused further spread of high topography in the Nangqian area. The tectonic development history of the Nangqian region indicates that the growth of the Tibetan Plateau is episodic and synchronous but with varying amplitudes.