Late Quaternary deformation features along the Anninghe Fault on the eastern margin of the Tibetan Plateau

Abstract

On the eastern margin of the Tibetan Plateau, the Anninghe, Zemuhe and Xiaojiang faults comprise a N–S-trending active left-lateral fault system extending more than 700km. The northernmost Anninghe Fault extends for ∼200km, consisting of two sub-parallel N–S trending strands. Along the western strand, the fault traces occur almost strictly along the broad and flat Anninghe valley, displacing high terraces, alluvial fans and tributary channels of the Anninghe River. The eastern strand, on the other hand, cuts through the steep mountain slopes, with prominent rectilinear upslope-facing scarps and shutter ridges against pounded fluvial sediments from the east. The displacements along the eastern strand are much larger than that along the western strand, indicating the eastern strand is the major fault absorbing the E–W shortening. This study demonstrates that the Anninghe Fault is now acting as a relief-building boundary fault and absorbing the E–W compression under the eastwards motion of the Tibetan Plateau. Accordingly, the Anninghe region is a topographic transition area from steep relief to low gradient topography. The variation in topographic gradient is consistent with the differing tectonic regime between southern and northern parts of the Tibetan Plateau.