Apatite and zircon (U–Th)/He thermochronological evidence for Mesozoic exhumation of the Central Tibetan Mountain Range

Abstract

The Central Tibetan Mountain Range (CTMR) exposes the oldest strata in the Qiangtang Terrane and may record the most complete exhumation history prior to and post‐collision of India and Asia. This article presents apatite and zircon (U–Th)/He thermochronology data of granites from the CTMR. Zircon (U–Th)/He single grain ages range from 116 to 191 Ma, while apatite (U–Th)/He single grain ages vary from 54 to 94 Ma. Thermal modelling results based on (U–Th)/He ages of apatite and zircon indicate that episodic rapid exhumations occurred at the Middle‐Late Jurassic and the Late Cretaceous, respectively. The Middle‐Late Jurassic exhumation is consistent with the provenance analysis of Jurassic strata in the South (SQT) and North Qiangtang Terrane (NQT) which suggested they were derived from the CTMR. This stage of rapid exhumation might be attributed to the northward ridge subduction of the Bangong‐Nujiang Ocean. The Late Cretaceous relatively rapid exhumation is compatible with the angular unconformity between the Abushan Formation and the underlying marine strata. This stage of exhumation may be caused by the collision between Lhasa and QT. Our results, combined with the crust shortening and adakitic rocks in the SQT during the Late Cretaceous, provide robust evidence for crustal thickening and early uplift of central Tibetan Plateau prior to the India‐Asia collision. The CTMR experienced very low exhumation since the early Eocene, implying that low‐relief topography had been established at high elevation with internal drainage prior to India‐Asia collision.