新近纪以来东帕米尔与西南天山对接过程的沉积学限定

Affected by collision of India and Asia in the early Cenozoic and the following continuous convergence, large-scale northward extension happened in the Pamir and the South Tian Shan started to uplift since Neogene. They interacted in the western Tarim Basin. The remarkable interaction process influenced Cenozoic tectonic, sedimentary and climatic evolution of southwestern Tarim Basin, have great scientific significance and research value.. This project chooses the East Pamir-Southwest Tian Shan convergent zone as study object, taking spatial-temporal evolution of sedimentary features and provenance of late Cenozoic succession in the convergent zone as the line and conduct researches about sedimentary response in the convergent zone. Our project takes the late Cenozoic Wuheshalu profile in the eastern convergent zone, west of Wuqia County in Xinjiang Province as the key, combine detrital zircon provenance analysis, paleocurrent measurement, conglomerate counting with sedimentary facies analysis and compare with previous researches in representative profiles in foreland of Pamir and South Tian Shan. Based on comprehensive analysis of spatial-temporal evolution of sedimentary features and provenance of late Cenozoic succession in the convergent zone, to constraint the interaction process of East Pamir and Southwest Tian Shan since Neogene.

受印度板块和欧亚板块在新生代早期的碰撞和后续的持续汇聚作用影响，新近纪以来帕米尔构造带发生大规模向北扩展，南天山开始造山抬升。两者在塔里木盆地西缘发生对接。这一对接过程对塔西南地区的新生代构造、沉积和气候的演化都产生了重要的影响，具有重大的科学意义和研究价值。. 该项目选择东帕米尔与西南天山对接带作为研究对象，以对接带地区晚新生代层系的沉积学特征和物源的时空变化为主线，开展东帕米尔与西南天山对接过程的沉积响应研究。项目拟选择对接带东部新疆乌恰县以西的吾合沙鲁乡晚新生代剖面作为重点，将碎屑锆石物源分析、古水流向统计、砾石统计等手段与沉积相分析方法相结合，并与南天山山前和帕米尔山前代表性剖面的前人成果进行对比，综合分析对接带区域的晚新生代地层沉积特征与物源变化的时空规律，来限定东帕米尔与西南天山新近纪以来的对接过程。

本项目通过对帕米尔北缘和东北缘山前地区和喀什凹陷12条古近纪沉积序列的沉积相对比和对帕米尔-南天山对接带地区吾合沙鲁剖面晚新生代沉积序列的沉积学与物源分析，研究了帕米尔构造带的古近纪构造活动特征及其在早中新世以来与南天山的汇聚过程。主要得出了以下结论：.一、喀什凹陷、帕米尔北缘和东北缘山前地区古近纪沉积序列的沉积相对比表明，古近纪时期就已经存在的帕米尔弧形特征比新近纪以来帕米尔逐渐变形形成弧形特征的模型更为合理。前人所认为的帕米尔在中新世之前其北缘与西昆仑齐平并在新近纪以来才发生向北推进并不合理。帕米尔内部的先存岩石圈薄弱带使得印度板块和亚洲板块碰撞的应力能在碰撞发生之后快速传递到其北缘和东北缘。.二、吾合沙鲁剖面晚新生代沉积序列和锆石U-Pb年龄表明北帕米尔的三叠系火成岩在早中新世（约19 Ma）以来一直是吾合沙鲁剖面的主要物源区。上新世沉积的碎屑锆石和砾岩的砾石统计结果表明北帕米尔依然是其主要物源区，而南天山在上新世早期（约5 Ma）向帕米尔-南天山对接带地区提供了少量物源。在约3 Ma，吾合沙鲁剖面的物源再次被北帕米尔物源所主导。