An immediate response to the Indian-Eurasian collision along the northeastern Tibetan Plateau: Evidence from apatite fission track analysis in the Kuantan Shan-Hei Shan

Abstract

The Tibetan Plateau offers an ideal region for understanding the processes of continental collision and related intracontinental deformation. However, when the Cenozoic deformation was initiated in the present northeastern margin of the plateau, >2000 km north to the Indian-Eurasian collision front, remains an issue in debate. Two competing end-member models have been proposed, involving immediate deformation response and progressive deformation propagation. Solving this problem partly relies on determining whether there was contemporaneous deformation with initial Indian-Eurasian collision along the northeastern margin of the Tibetan Plateau. In this study, we employ apatite fission track (AFT) analysis to shed new light on the exhumation history of the Kuantan Shan-Hei Shan along the northeastern margin of the Tibetan Plateau, with a motivation to determine whether deformation-related exhumation during initial collision stage occurred in the region. The 22 granite samples produce AFT ages ranging from 22.3 ± 2.6 Ma to 175 ± 18 Ma and mean track lengths from 11.17 ± 2.26 μm to 13.63 ± 1.93 μm. Thermal history modeling indicates five episodes of rapid exhumation-related cooling, which took place in the early Jurassic, early Cretaceous and late Cretaceous, during/since the Eocene and since the middle Miocene. The exhumation events prior to the Cenozoic are attributed to far-field responses of successive closure of fossil oceans and assembly of blocks along the southern margin of the Eurasian continent. The Eocene exhumation along the Kuantan Shan-Hei Shan is speculated to represent an immediate response to the initial Indian-Eurasian collision. These results lend support to the immediate deformation response model along the northeastern plateau. The episodic exhumation observed in this study, combined with previous geophysical findings, implies that the Kuantan Shan-Hei Shan represents the southern margin of the Alashan Block, serving as a significant and long-lived lithospheric weak zone susceptible to intracontinental deformation during episodes of far-field tectonic event.