青海可可西里大地构造基本特征

BASIC GEOTECTONIC CHARACTERISTICS OF THE HOH XIL REGION OF QINGHAI PROVINCE, CHINA

在可可西里地区发现的晚古生代蛇绿混杂岩及不整合于其上的晚二叠世—早三叠世海滩亚相石英砂岩表明此区曾存在过古特提斯洋,早二叠世末古特提斯基本闭合。晚二叠世—早三叠世为相对稳定阶段。中、晚三叠世海侵,沉积了巨厚复理石。三叠纪末—早侏罗世发生了强烈的造山作用,形成造山带,可可西里地区进入陆内演化阶段。

A set of the Early Carboniferous-Early Permian ophiolitic melanges, unconformably overlain by the Late Permian-Early Triassic beach-subfacies quartzose sandstones, is first discovered in Hoh Xil region, Qinghai Province in 1990, which indicates that Paleotethys existed in the Early Carboniferous-Early Permian. The ocean crust began to subduct beneath the North China Block in Kunlun in the Late Carboniferous, marked by the beginning of Arc-type magrnatic activity and by formation of an arctrench system. At the end of the Early Permian the North Qiangtang Block weakly collided with the southern margin of the North China Block, which is demonstrated by a wide(>100km) preserved accretionary wedge. A land connection established between the North China Block and the North Qiangtang Block, which provided the Dicynodont a direct route from Indochina to Central Asia. The region was relatively stable during the Late Permian-Early Triassic. A thick(5—10km) flyschoid sequence was deposited in a trough during the Mid-Late Triassic. The strong orogenesis occurred during the end of the Triassic to the Early Jurassic. This resulted in the final close of the Paleotethys and the formation of the Indosinide. After this, intracontinental regime characterizes the Yanshanian and Himalayan tectonism. Since the Oligocene, the region has been uplifted as a whole, which resulted in the appearance of the plateau plain.