Strike-Slip Rate of the Kangding Fault System: Implications for Regional Tectonic Evolution of the Tibetan Plateau

Intensive field investigation on the Kangding fault system in 1997-1998 revealed that: 1) strike-slip rates along the Anninghe, Zemuhe, and Xiaojiang faults are about 6-10 mm/yr, 5.8-8.5 mm/yr, and 13.0-16.5 mm/yr, respectively; 2) the central part of the Kangding fault includes not only the Anninghe and Zemuhe faults, but also the Puxionghe-Butuo fault, located to the east of the Anninghe fault; and 3) total offset along the Kangding fault system is about 160 km, of which 90 km are accommodated by the Anninghe and Zemuhe faults and the remaining 70 km by the Puxionghe-Butuo fault. These results suggest that the Late Quaternary strike-slip rate of about 15+/-2 mm/yr is approximately uniform along the entire length of the fault system. By approximating the geometry of the arc-shaped Kangding fault system as a segment of a small circle on the Earth's surface, the fault system's approximately uniform strike-slip rate of 15+/-2 mm/yr corresponds to clockwise rotation of the Southeastern Tibetan Block relative to the Northeastern Tibetan Block at an angular velocity of 0.431-0.563 deg/Myr around a pole at (21° N, 88° E). Moreover, the total offset along the Kangding fault system suggests that the extent of lateral extrusion of the Southeastern Tibetan Block is about 160 km relative to the Northeastern Tibetan Block, and 200-240 km relative to the Tarim-North China block. If a uniform slip rate of 15+/-2 mm/yr has been maintained throughout the entire history of the Kangding fault system, it would have taken 11+/-1.5 Myr for the Kangding fault system to attain a total offset of 160 km. This implies that left-lateral movement on the Kangding fault system, and other strike-slip faulting in eastern Tibet, started at 11+/-1.5 Myr. Also, the approximately uniform strike-slip rate along the Kangding fault system implies that the Longmenshan thrust zone is not active, or at least that its activity has been very weak since the Late Pleistocene.