Eocene to Pliocene exhumation history of the Tianshui-Huicheng region determined by Apatite fission track thermochronology: Implications for evolution of the northeastern Tibetan Plateau margin

This study presents new apatite fission-track (AFT) data from the Tianshui-Huicheng region, which is situated in the northeastern margin of the Tibetan Plateau. AFT results (including 19 detrital and 13 bedrock samples) show that deposition in the Tianshui-Huicheng basin range from early Eocene to late Miocene– Pliocene and most of the apatites derived from the Western Qinling orogenic belt, reflecting one rapid exhumation episode (at 34–29 Ma) and two phases of volcanism (at 23–18 Ma and ca. 13 Ma). The exhumation history of the Tianshui-Huicheng region is likely related to episodic tectonic activity and directly linked to the kinematics of active deformation of the Tibetan Plateau. Active processes deciphered from the detritus indicate that deformation reached the northeastern Tibetan Plateau margin as early as ca. 49 Ma, which is manifested by the initiation of the Tianshui-Huicheng basin. The 23–18 Ma event, linked to the lithosphere deformation of the Western Qinling and the Neogene basin formation along the Tianshui-Huicheng region. By modeling the bedrock samples, an 8–4 Ma event was revealed which resulted from the intense deformation of the Tianshui-Huicheng region.