Late Cenozoic Systematic Left-Lateral Stream Deflections along the Ganzi-Yushu Fault, Xianshuihe Fault System, Eastern Tibet

Abstract

The Xianshuihe fault system (XSF) is one of the most active faults in eastern Tibet, China. In this study, we document the distribution of stream deflections along the Ganzi-Yushu segment of the XSF at scales of 2.5 m to 80 km. The total offset along this fault suggests that left-lateral movement began at ~8-5.6 Ma if the Holocene slip rate has remained steady over this time interval. From Dengke in the southeast to Dangjiang in the northwest along the Ganzi-Yushu fault, the documented total geological offset decreases from ~80 to ~39 km, whereas the deflections of the Yalong, Batang, Jielong, and Dangjiang rivers, almost all of which initiated around early Quaternary time, show gradually decreasing offsets from 30 ± 2 km to 16 ± 1 km in the same direction. This implies that about 41 km and 14 km offset are accommodated by transtensional and transpresional structures such as pullapart basins and thrust faults along different parts of the fault at different times; this is also consistent with a northwestward decrease in the Holocene slip rate along the XSF, from 10 to 14 mm/yr around Dengke to ~7 mm/yr around Dangjiang. Thus the spatial and temporal evolution of stream patterns along the XSF supports the hypothesis that the tectonic evolution of eastern Tibet is largely characterized by distributed deformation.