第四纪磨拉石组分与青藏高原隆升的关系——对新疆叶城柯克亚剖面第四系砾石成分测量结果的认识

青藏高原北缘的第四纪磨拉石沉积反映了高原所经历的隆升和剥蚀过程。本次工作对新疆西昆仑山前柯克亚剖面第四系磨拉石进行了砾石测量和统计。其结果为:砾石成分主要是沉积岩类,尤其在下部,以砂岩等碎屑岩为主;向上有较多的碳酸盐岩砾石,其中变质岩砾石较少,基本未见片麻岩砾石。这一结果表明当时的物源区主要是由中、新元古界、古生界和中生界的沉积岩系组成的,与现代地表在铁克里克及西昆仑出露的大套变质岩系明显不一致。由此可见,该地区在第四纪早期尚未具有现代地表的地质构造面貌特征,或者说尚未达到现今的隆起高度。现在铁克里克和西昆仑地区出露的大面积古老变质岩系是2.4Ma以后的构造隆升造成的。

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.