Tectono-morphological evolution of the Minxin-Wudu area on the northeastern margin of the Qinghai-Tibet Plateau and plateau uplift

Abstract：Located on the northeastern margin of the Qinghai-Tibet Plateau, the Minxian-Wudu area in the West Qinling is tectonically a transition zone between two major tectono-morphological units in China. Tectono-morphological study shows that four planation surfaces are developed in this area; they are planation surfaces I (mountain top surface), II (main planation surface) and III and IV (erosional surface), which formed before the Middle Cretaceous-late Paleocene and at 3.6, 2.5 and 1.8 Ma respectively. Four to seven terraces are developed for main rivers in this area, and terrace IV and those of still smaller orders in these rivers have similar characteristics. The variations in attitude of these planation surfaces and terraces indicate that the crustal uplift in the area occurred in several stages and heterogeneously：the average uplift rate has been 0.42–0.57 mm/a and the 3.6–1.8 Ma period was a stage of rapid crustal uplift; the uplift rate became low at 1.8 Ma but the uplift accelerated markedly since the late Pleistocene (0.15 Ma), suggesting that the plateau is now in a new stage of uplift acceleration.