拉萨地块与相邻地块二叠纪古生物地理对比研究

Tethys is the cradle for geology. Its evolution of land and sea, the landscape of the continents and geological activities are predominant factors on the tectonic evolution of continents. A series of oceans have appeared and closed between the northern and southern continents. The Qinghai-Tibet Plateau has recorded all the complex orogeny of the Tethys, which serves as an ideal place to study geodynamics. However, due to the complexity of the evolution and formation of the Qinghai-Tibet Plateau, the rifting time and process of the Tibetan blocks, and the opening time of both the Bangong-Nujiang and the Neotethys Ocean have been the contentious issues that deserves an intensive study.. This project aims to provide a detailed study on the Permian strata and faunas from many sections in the Lhasa Block as well as other sections in the South Qiangtang Block, Shan Plateau of Myanmar (Sibumasu Block) and Salt Range of Pakistan (Indian Plate). The key objectives of the project are: (1) Correlating the Permian paleobiogeography within the Lhasa Block in order to check if the evolution of paleobiogeography is synchronous in the whole Lhasa Block; (2) Knowing the evolution patterns of the Permian paleobiogeography in the Lhasa Block; (3) Correlating of Permian paleobiogeography between the Lhasa Block and the South Qiangtang-Baoshan-Sibumasu blocks in the north as well as the Indian Plate in the south to explore their difference. The ultimate goal of this project is to resolve the significant scientific problems with respect to the opening time for both the Bangong-Nujiang Ocean and the Neotethys Ocean. This will serve as a basis for further paleogeographic and oceanic reconstructions in the Tethyan region.

特提斯构造域的地质演化是地质历史时期的重大事件。青藏高原保存了特提斯最复杂的洋盆演化记录，是研究特提斯地球动力学的窗口。但其演化过程异常复杂，在西藏诸块体如何从冈瓦纳大陆裂解，何时裂解以及班公湖-怒江洋和新特提斯洋何时打开的重大科学问题上争议颇多，亟待深入研究。. 本项目基于申请者多年在青藏高原及其邻区的研究积累，重点选择拉萨地块多个地区的二叠纪地层和动物群为研究对象，并结合南羌塘地块、Sibumasu地块（缅甸掸邦高原）、印度板块（巴基斯坦盐岭地区）的研究。目的是考察拉萨地块内部二叠纪古生物地理变化趋势是否一致、总结拉萨地块二叠纪古生物地理演化的特征、对比拉萨地块和北面南羌塘-保山-Sibumasu地块及南面印度板块北缘的古生物地理演化的差异性。项目的最终目标是用古生物地理学方法推测班公湖-怒江洋和新特提斯洋的开启时间，为进一步开展特提斯地区古地理和洋盆演化重建提供依据。

西藏中特提斯洋和新特提斯洋的打开时间是认识特提斯地球动力学的基础。本项目旨在通过西藏拉萨地块以及相邻地区二叠纪地层、生物群及古生物地理的研究，判断拉萨地块同相邻地块的古地理关系，约束中特提斯洋和新特提斯洋的打开时间。项目针对拉萨地块、南羌塘地块、喜马拉雅地区、腾冲地块、缅甸掸邦高原开展系统地层古生物研究工作。研究证实：（1）西藏拉萨地块是一个非常稳定的地块，整个地块以下二叠统冰碛岩及中上二叠统碳酸盐岩为主；而南羌塘地块存在东西向的差异性，东部多玛地区下二叠统吞龙共巴组和上二叠统吉普日阿群之间存在不整合面，中部双湖地区存在玄武岩和灰岩组成的鲁谷组，两者地块完全不同；再者横向上，拉萨地块的地层显示在古地理上它只和腾冲地块相似，在喀喇昆仑断裂以西没有地块与拉萨地块相似；（2）古生物地理上南羌塘地块至少从早二叠世空谷期开始出现大量特提斯暖水动物群，但整个拉萨地块空谷期仍然是以凉水动物群为主。因此，中特提斯洋的打开时间至少是在空谷期以前；（3）缅甸掸邦高原的地层古生物研究把原来的Sibumasu地块分为两个部分，西部称为Irrawaddy地块，东部称为Sibuma地块，其中Sibuma地块和保山地块及南羌塘地块有古生物地理亲缘性；而Irrawaddy地块和腾冲以及拉萨地块有古生物地理亲缘性，Sibuma地块和Irrawaddy地块之间隐含的Medial-Myanmar 缝合带代表了中特提斯洋在东南亚的遗迹；（4）拉萨地块的古生物地理研究显示从早二叠世至晚二叠世，古生物地理从冷水动物群转变到暖水动物群，但相比之下喜玛拉雅地区古生物地理未变；再者特色有孔虫Shanita-Hemigordiopsis动物群的分布揭示，它的分布受新特提斯洋的洋流控制，因此新特提斯至少从中二叠世以前就已经打开；（5）中特提斯洋和新特提斯洋都在二叠纪的不同时间打开，这种异速打开与俯冲板块拖拽模式较符合。本项目的研究揭示了中特提斯洋和新特提斯洋的古地理演变模式，为理解特提斯地球动力学提供了重要的证据。