羌塘中部后中新世叠瓦式逆冲推覆构造

Post-Miocene Imbricate Thrust Structures in Middle Qiangtang, Western China

对青藏高原地壳缩短率 (量 )的测量是诠释青藏高原巨厚地壳成因的关键 .以前的研究认为青藏内部新生代的地壳缩短不超过 4 0 % .通过在羌塘地体中部达卓玛盆地内细致的地层测量 ,我们发现了形成于中新世之后的、典型的叠瓦式逆冲推覆构造 .断层均以高角度向北倾斜 ,累计缩短率在 6 7%以上 .此种变形及其强度在南羌塘地区具有代表性 ,显示青藏内部的地壳缩短对青藏高原巨厚地壳的形成可能起着重要的作用 。

There are two radically different interpretations of the development of the Tibetan plateau: doubling the continental crust by replacement of the Tibetan upper mantle by underthrust Indian continental crust, or by the interior shortening of the Tibetan crust due to the India/Eurasian convergence. Although the Indian continent could indeed be underthrust beneath the Tibetan plateau, the underthrusting is limited to the south of the Bangonghu_Nüjiang suture. And former investigations proposed that Cenozoic crustal shortening of the plateau generally is less than 40%. Therefore, the mechanism of the Tibetan plateau still is a focal point of considerable debate and the magnitude of Cenozoic crustal shortening within the Tibetan plateau is of key importance to the models for its development. Recently, we conducted detailed measurement twice at a scale of 1∶ 2 000 on the Dazhuoma structural section in middle Qiangtang. Our fieldwork, together with seismic and boring exploration in another structural section of nearby area, shows that the late Cenozoic crustal shortening within southern Qiangtang is more than 50%. This indicates that the interior crustal shortening within the plateau can play a crucial role in the doubling of the Tibetan crust.