Relation between the components of Quaternary molasse and uplift of the Qinghai-Tibet Plateau--Preliminary understanding of the results of measurements of the Quaternary pebble composition at the Kokyar section, Yecheng, Xinjiang

Quaternary molasse deposits on the northern margin of the Qinghai-Tibet Plateau indicate the processes of uplift and erosion of the plateau.Pebbles of Quaternary conglomerate at the Kokyar section in the front of the western Kunlun Mountains.,southern Xinjiang,have been measured and calculated.The results show that the components of the pebbles are mainly sedimentary rocks and especially the pebbles in the lower part of the section consist dominantly of sandstone and other clastic rocks.Upward,there are more pebbles of carbonate rocks,of which pebbles of metamorphic rocks are scarce and pebbles of gneiss are in the main absent.This result indicates that the provenances were mainly made up of Meso -and Neoproterozoic,Paleozoic and Mesozoic sedimentary rocks,which is notably inconsistent with widespread outcropping of metamorphic rocks in Tekilik and the western Kunlun Mountains now.So the authors come to the conclusion that there were no features of modern surface geological structure in Tekilik and the western Kunlun area during the early Quaternary;in other words,the mountains had not attained the present height then.The extensively exposed ancient metamorphic series that we see in Tekilik and the western Kunlun area today resulted from tectonic uplift after2.4Ma.