Tectonic characteristics and formation mechanism of Cenozoic grabens in the source region of the Yangtze River, China

Field mapping reveals that the nearly N-S-trending grabens are the present most prominent structural features in the source region of the Yangtze River, which are also the northernmost grabens ever found on the Qinghai-Tibet Plateau. There are four major grabens distributed in the region, namely the Wenquan graben, Changcuo graben, Danglacuonama graben and Tuotuo River graben. Fault chronology and sedimentation of the downfaulted basins indicate that extensional deformation in the study region was initiated in the late Miocene to early Pliocene at least, which has had a marked controlling effect on the present geomorphologic framework and drainage pattem in the region. The main drainage system in the source region of Yangtze River formed and developed by riverhead erosion along the N-S-trending grabens and normal faults. The Cenozoic extensional grabens on the Qinghai-Tibet Plateau are the product of rapid uplift of the plateau caused by the deep dynamic mechanism after earlier strong crustal shortening.