Episodic cooling of the Hannan-Micangshan Dome at the northern margin of the Yangtze Block, Central China: Response to progressive convergence in the eastern Tethys since the Mesozoic

Abstract

The Hannan-Micangshan Dome (HMD) is a Meso-Cenozoic intra-continental compressional tectonic belt that provides an excellent natural laboratory to study intra-continental deformation processes and geodynamic mechanisms in Central China. Although many low-temperature thermochronological studies have been conducted in the HMD, the timing of initial cooling/exhumation, rapid exhumation phases and their relationship to progressive convergence in the eastern Tethys are still poorly constrained. In this study, we present new multiple thermochronological analyses of apatite (AFT) and zircon fission track (ZFT), hornblende and muscovite Ar-Ar, and zircon U-Pb dating of granitoid and sedimentary rocks from the HMD. Granitoids from the HMD yield Proterozoic zircon U-Pb ages and slightly younger hornblende and muscovite Ar-Ar ages, indicating rapid cooling after emplacement. ZFT dating of granitoids yielded apparent ages of ∼208–140 Ma. AFT dating of Triassic-Cretaceous sandstones and Proterozoic granitoids yielded apparent ages between ∼117 and ∼58 Ma. Thermal modeling results suggest that the HMD has experienced the onset of cooling and exhumation since the Early Jurassic followed by three phases of rapid cooling/exhumation during the Late Jurassic-Early Cretaceous (∼160–100 Ma), Middle Eocene (∼40 Ma) and since the Late Oligocene-Early Miocene (∼23–15 Ma). The initial exhumation in the HMD by the Early Jurassic may be related to the closure of the Paleo-Tethys Ocean between the Kunlun and Qiangtang terranes. The Late Jurassic-Early Cretaceous rapid exhumation in the HMD can be related to the basement-involved thrusting triggered by the far-field effects of the ongoing collision between the Qiangtang and Lhasa terranes following the closure of the Meso-Tethys since the Late Jurassic. Two phases of rapid Cenozoic exhumation by the Middle Eocene and since the Late Oligocene-Early Miocene in the HMD were attributed to the far-field stress effects of the collision between the India and Asian plates and the lateral growth of the Tibetan Plateau. Therefore, we proposed that the episodic cooling since the Early Jurassic of the HMD at the northern margin of the Yangtze Block can be interpreted as being related to the progressive convergence in the eastern Tethys since the Mesozoic.