Active Faulting Pattern, Present‐day Tectonic Stress Field and Block Kinematics in the East Tibetan Plateau

Abstract

Abstract:This paper examines major active faults and the present‐day tectonic stress field in the East Tibetan Plateau by integrating available data from published literature and proposes a block kinematics model of the region. It shows that the East Tibetan Plateau is dominated by strike‐slip and reverse faulting stress regimes and that the maximum horizontal stress is roughly consistent with the contemporary velocity field, except for the west Qinling range where it parallels the striking of the major strike‐slip faults. Active tectonics in the East Tibetan Plateau is characterized by three faulting systems. The left‐slip Kunlun‐Qinling faulting system combines the east Kunlun fault zone, sinistral oblique reverse faults along the Minshan range and two major NEE‐striking faults cutting the west Qinling range, which accommodates eastward motion, at 10–14 mm/a, of the Chuan‐Qing block. The left‐slip Xianshuihe faulting system accommodated clockwise rotation of the Chuan‐Dian block. The Longmenshan thrust faulting system forms the eastern margin of the East Tibetan Plateau and has been propagated to the SW of the Sichuan basin. Crustal shortening across the Longmenshan range seems low (2–4 mm/a) and absorbed only a small part of the eastward motion of the Chuan‐Qing block. Most of this eastward motion has been transmitted to South China, which is moving SEE‐ward at 7–9 mm/a. It is suggested from geophysical data interpretation that the crust and lithosphere of the East Tibetan Plateau is considerably thickened and rheologically layered. The upper crust seems to be decoupled from the lower crust through a décollement zone at a depth of 15–20 km, which involved the Longmenshan fault belt and propagated eastward to the SW of the Sichuan basin. The Wenchuan earthquake was just formed at the bifurcated point of this décollement system. A rheological boundary should exist beneath the Longmenshan fault belt where the lower crust of the East Tibetan Plateau and the lithospheric mantle of the Yangze block are juxtaposed.