Late Cenozoic orogenic history of Western Qinling inferred from sedimentation of Tianshui basin, northeastern margin of Tibetan Plateau

摘要

The Western Qinling orogenic belt marks the northeastern margin of the Tibetan Plateau. Its late Ceno-zoic orogenic history is recorded in an excellent sedimen-tary sequence exposed in the Tianshui sub-basin of the Longzhong basin. According to the magnetostratigraphic analysis from the Yaodian and Lamashan sections, we speculate that the late Cenozoic Tianshui basin accumulated lacustrine/floodplain deposits from — 14.8 to ～2.6 Ma. In addition, detrital apatite fission-track thermochronologic and paleocurrent data reveal that the detritus of the Tianshui basin mostly derived from the Western Qinling and that the youngest population age represents a ～14Ma volcanic intrusion, which can be related to the lithospheric defor-mation and uplift of the Tibetan Plateau. Furthermore, two stages of variations in depositional facies and average accumulation rates were attributed to the pulse uplift and deformation of the Western Qinling at 9.2-7.4 and ～3.6 Ma.