Uplift of the Emei Shan, western Sichuan Basin: Implication for eastward propagation of the Tibetan Plateau in Early Miocene

Abstract

The Emei Shan stands on the southeast side of the Longmen Shan. It marks the southeastern most edge of the eastern margin of the Tibetan Plateau (EMTP) and towers above the Sichuan Basin to its east, with the highest peak being 3099m. A large number of structural and thermo-chronological studies have been published focused on the Longmen Shan orogen, which is considered to be the northern part of the EMTP. However, for the southern part of the EMTP where the Emei Shan lies, its tectonics and uplift history are still poorly understood. This paper dates five granite samples from the Emei Shan batholith using the apatite fission track (AFT) method. The boundary faults of the Emei Shan and structural deformation in adjacent region are also investigated and mapped in detail. (1) In Miocene time, compressional stress from the eastward extrusion of the EMTP caused large-scale thrusting and mountain uplift along narrow Longmen Shan in northern EMTP, in contrast to southern EMTP where a broad and gentle Yaan−Emei Shan fold belt absorbed most of the stress. By Pliocene time, the southeastward extrusion of the Tibetan Plateau caused the transpressional stress and rotated the Chuandian fragment along the Xianshuihe−Xiaojiang fault belt. As a consequence, the Emei Shan region was intended northeastwards into the Sichuan Basin, bounded by two strike-slip faults on its north and southeast sides. (2) The AFT results show the Emei Shan uplifted since ∼25–20Ma ago. The threshold and main stage of uplift of the Emei Shan possibly lagged behind the Longmen Shan of approximately 5Myr. As the leading edge of fold belt, uplift of the Emei Shan indicated the eastward propagation of the EMTP was time-transgressive from Late Oligocene to Middle Miocene.