Neotectonics of the Bailongjiang and Hanan faults: New insights into late Cenozoic deformation along the eastern margin of the Tibetan Plateau

Abstract

AbstractThe way that far-field stresses and deformation propagated eastward in response to the growth and extrusion of the northeastern Tibetan Plateau remains a crucial scientific issue. This paper focuses on the Bailongjiang and Hanan faults, which are the easternmost part of the East Kunlun fault in northeast Tibet. Based on new field geological investigations, structural data, satellite imagery interpretation, and optically stimulated luminescence and 14C dating results, this paper presents the structural geometry and neotectonic activities of the two faults. The ∼200-km-long Bailongjiang fault, bounding the Bayan Har block in northeast Tibet, consists of two segments. Along the western segment, late Pleistocene lacustrine-facies deposits and Holocene activities were discovered in a great fault scarp. The left-slip rate of the fault is estimated to be ∼1.73–2.61 mm/yr, with an elapsed time of ∼2205 yr after a catastrophic paleoseismic event greater than M 7.2 ruptured the fault. The eastern segment splits into two branches and shows a positive flower structure where a pull-apart basin developed, filled with ∼200-m-thick mudstone and argillaceous siltstone, which record the mid-late Miocene deformation of the Bailongjiang fault. The Hanan fault features reverse faulting caused by NNW-SSE compression in the late Cenozoic. The two faults, together with the Maqên-Maqu-Tazang fault, confine the area of a strip block, the eastward extrusion of which was accommodated by thrusting due to the resistance of the stable Bikou massif since the late Cenozoic, which led to decreasing slip rates along the easternmost part of the Kunlun fault.