Initiation and Evolution of the Shanxi Rift System in North China: Evidence From Low-Temperature Thermochronology in a Plate Reconstruction Framework

摘要

The Shanxi Rift System (SRS) is a prominent intracontinental rift in eastern Eurasia. However, its tectonic origin remains enigmatic, as the timing of rift initiation and its subsequent evolution is not well constrained. To evaluate the cooling history of rift flanks, we present joint apatite fission track (n = 15) and apatite (U-Th-Sm)/He (n = 62) thermochronological study across the Huo Shan and the Zhongtiao Shan in the central and southern SRS, respectively. Inverse modeling of the thermochronological data yields two episodes of enhanced exhumation during the Cenozoic. Both ranges record rapid cooling circa 50-35 Ma, coeval with a phase of widespread rifting across entire North China. Data from the Zhongtiao Shan record renewed cooling from similar to 8 Ma to the present, following a protracted near-isothermal condition. Considering the SRS in the context of plate reconstructions, we propose that the Eocene rift initiation is triggered by the subduction of the trench-parallel Izanagi-Pacific mid-ocean ridge followed by subduction of the Pacific plate. Tectonic quiescence along the Shanxi rift during Oligocene and Miocene time reflects slow thermal subsidence as the Pacific subduction regime was established. In late Miocene, faults associated with the SRS were reactivated in dextral transtension linked to fault systems that extend outward from the northeastern Tibetan Plateau. This kinematic reorganization implies a fundamental change in force balance throughout North China. Overall, our results reflect the changing influence of tectonic regimes along the eastern Eurasian plate boundary and intracontinental deformation associated with the India-Eurasia collision.