Apatite (U-Th)/He Thermochronological Constraints on the Landscape Evolution Linked to the Normal Faulting in Taishan Mountain, Eastern China

Abstract

Taishan Mountain in the eastern China is a normal-fault-controlled range that formed during the Meso-Cenozoic, in response to large-scale extension and lithospheric thinning of the North China Craton. However, constraints on the timing of the polyphase extensional events which formed the Taishan edifice remain poorly resolved, hindering a detailed understanding of the landscape evolution of this prominent mountain. Here, we conducted apatite (U-Th)/He dating on sixteen samples from three profiles perpendicular in the Taishan Mountain, with a major view to control structures in Taishan Mountain and to resolve the Meso-Cenozoic landscape evolution. The newly determined apatite (U-Th)/He ages show a wide variation range of ~113 to 30 Ma, indicating a slow and protracted cooling history. The inverse thermal history modeling results reveal two pulses of enhanced cooling at ~80 to 60 and 55 to 50 Ma, which we interpret as exhumation related to normal fault activity. Furthermore, one-dimensional modeling indicates that the magnitude of tectonic exhumation is constrained at ≥15 m/Myr across the Yunbuqiao, Zhongtianmen, and Taishan Piedmont faults. Integrating this study and published studies, we suggest that Taishan Mountain underwent four-stage evolution since 100 Ma: (1) the whole Taishan Mountain commenced a continuous and slow exhumation under a weaker tensional environment at ~100 to 80 Ma, (2) the joint growth and interactions within a normal fault system resulted in rapid uplift and promoted the formation of the Proto-Taishan Mountain at ~80 to 60 Ma, (3) the Taishan Mountain underwent exhumation at ~55 to 50 Ma, interpreted as a tectonic response to the Taishan Piedmont Fault, and (4) the last stage (~50 to 0 Ma), the Taishan Mountain experienced protracted exhumation related to normal faulting until now. We attribute the extensive normal faulting to the subduction and slab rollback of the Izanagi-Pacific Plates, which shaped the present-day geomorphology of Taishan Mountain.