西藏的构造演化历史及其特点

<正> 西藏位于我国西南边陲、北起唐古拉山,南至喜马拉雅山,自然条件较差,但地质位置重要,是研究大陆上板块构造和多旋回构造运动的良好场所。笔者有幸参加中国地质科学院组织的几个研究项目工作,工作中一直得到黄汲清老师的指导和关心,现将这些实地考察结果和同行的部分资料综合在一起,讨论一下西藏的构造演化历史及其多旋回构造运动特点。

THE TECTONIC DEVELOPMENT OF XIZANG AND ITS CHARACTERISTICS

Crystalline basements of the Precambrian and glaciomarine sediments of the Gondwana facies of the Carboniferous-Permian system are widely spread in the Xizang Plateau, suggesting that the Xizang Block was part of Gondwanaland. In the Early Mesozoic or at the end of Paleozoic, the Xizang Block began to be separated from the Gondwanaland. Then the large scale seafloor spreading or rift extension occurred in the continental basement. In the Mid-Late Mesozoic, the trench-arc system of the Yarlung Zangbo River and the Xainza-Nagqu Rift system of the mantle type in northern Xizang were formed. Both the Yarlung Zangbo River subduction zone and Dongqian-Deng-qen zone came into being due to the subduction and collision of plates. During the collision, the first uplifting of the Xizang Plateau took place from the Late Cretaceous to the Eocene. It ended the transgression history of Xizang. At the same time, it caused the regression in an all-round way. The second rising took place from the Eocene to the Oligocene. And the thirth took place from the Pliocene to the Pleistocene. The last one was the largest among the three in scale. The embryo of the Xizang Plateau was formed. After that, the Xizang Plateau rose again at the end of Early and Middle Pleistocene to form the present pattern of the Xizang Plateau.