塔里木盆地西北缘志留纪至二叠纪碎屑岩源区及其对天山古生代洋盆关闭时限的约束

Tiashan Mountains is located within central Asian continent and its occurrence is originated from the latest Paleozoic collisional orogeny following the closure of the Paleozoic ocean as its precursor and Cenozoic intracontinental orogeny related to collision of Eurasian with Indian plates. When the colsure of the ocean occurred has been a hot-debated and key issue in the geological field as it is of significance for renconstruction of both the earlier collisional orogenic process of the Mountians and ocean-continent framework within and amalgamation of Asian and Eurasian continents. Up to now, there are very contrative viewpoints on the issue among difirent geologists who are based mainly on data from investigations and researches into stratigraphy, magmatism and ancient oceanic remains exposed within the Mountains. This project plans to study sedimentary structures such as crossing bedding and ripple marks, compositions and ratios of detrital minerals and rocks, detrital zircons and structural deformation of the Silurian through Permian sedimentary sequences in the northwestern Tarim basin which are deposited in the Passive margin of Tarim continent south of the Paleozoic ocean as the precursor of the Tianshan Mountains, attempt to search for and determine the oldest layer of the sequences containing the debris come from the Tianshan Mountains, to discuss and ascertain the timing of closure of the ocean and collisional orogeny between the Paleozoic accretional margin within Tianshan Mountains with Tarim continents, and to provide scientific evidence for reconstruction of Paleozoic global ocean-continental framework and amalgamation of Aisian continent.

天山山脉位于亚洲大陆腹地，其形成演化经历了继古生代洋盆关闭发生的塔里木古陆与北部增生陆缘的碰撞造山和新生代陆内造山。其前身古生代洋盆关闭的时限，不仅与天山山脉早期的碰撞造山密切相关，也与亚洲乃至欧亚大陆古洋陆格局和大陆聚合过程的重建密切相关。基于对天山内部地层建造、岩浆岩和古洋岩石圈残片的研究，地质界产生了对天山前身古洋盆关闭时限截然不同的认识。本项申请基于塔里木古陆与天山之间在古生代期间被天山前身的古洋盆分隔这一事实，拟通过对塔里木盆地西北缘志留纪至二叠纪碎屑岩沉积构造、碎屑组分、碎屑锆石和构造变形特征开展研究，寻找和确定其中含有来自天山古活动陆缘和增生碰撞杂岩碎屑的最古老层位，探讨和确定天山造山带前身的古生代洋盆的关闭和碰撞造山的时限，为中亚地区古洋陆格局结束时限的确定及亚洲大陆聚合过程的重建，提供科学依据。

经过4年的研究，完成了计划的各项研究任务。从塔里木盆地西北缘古生代地层中获得了一批碎屑锆石和沉积作用方面的新资料。这些新资料揭示出，来自天山的碎屑物质，直到二叠纪早期才到达塔里木古陆北缘，柯坪地区夹有两套玄武岩的二叠纪地层是在早二叠世晚期至晚二叠世期间沉积的，即该区玄武岩是分别在早二叠世晚期和晚二叠世喷发的。这项研究表明塔里木古陆北缘面向的古生代洋盆是在石炭纪末期才关闭的。