帕米尔东北缘-西南天山南缘新生代构造旋转时空变化古地磁研究

The block rotation between Western Himalayan Syntaxis and Southwest Tian Shan is a vital point for deciphering the kinematics character of the Tibetan Plateau and adjacent region, process of regional geomorphy evolution, resource reforming, climatic change, etc. Palaeomagnetic researchs indicated that the block rotation had took place in this region during the Mesozoic-Cenozoic intervals, but the spatio-temporal variations of the block rotation between two tectonic systems is omitted. Basing on our previous works, this project using palaomagnetic method to deciphering the Cenozoic spatio-temporal block rotation between the Northeast margin of the Pamir and the South margin of the Southwest Tian Shan. Samples will be collected within the Cenozoic strata in four locations, superconducting magnetometer and other rock magnetic instruments will be used to measure the samples, principle component analysis will be used for calculating natural remanent magnetization directions, magnetic declination statistics will give the spatio-temporal variations of block rotation. The Cenozoic spatio-temporal variations of block rotation between the northeast margin of the Pamir and south margin of the Southwest Tian Shan will be used for deciphering the possible initial India-Erasia collision in this region by the similar value during Cenozoic. Synthesized the previous published results, the Cenozoic evolution history of the entire Tibetan Plateau and adjacent region will be consummated. This project has some innovation for the possible initial collision time in this region by the study of spatio-temporal variation of the block rotation, and discussing the Cenozoic tectonic evolution history of the Tibetan Plateau and adjacent region.

西构造结-西南天山两大体系的构造旋转对认识该区及整个高原运动学特征、地貌演化过程、资源改造、环境变化等至关重要，已有研究表明该区新生代存在一定的构造旋转，但缺乏两大构造体系新生代构造旋转时空变化研究。本次申请以前期研究工作为基础，以帕米尔东北缘和西南天山南缘四个采样地点的新生代地层为研究对象，对上述地区新生代地层进行系统的古地磁采样，应用超导磁力仪及各种磁学仪器进行测量，利用主成份分析、岩石磁学获取测量样品的天然剩磁方向，通过磁偏角统计获得该区新生代构造旋转时空变化，利用两者旋转配套性、旋转量数值近似性来尝试探讨两大构造体系对接的可能时限，综合已有成果完善该区及整个高原新生代构造演化过程。本次申请拟研究帕米尔东北缘-西南天山新生代构造旋转的时空变化，尝试探讨两大体系对接的可能时限，探讨该区及整个高原的新生代构造演化过程，具有一定的创新性。

通过对帕米尔东北缘-西南天山南缘碰撞系塔西南乌恰县城东的中新世乌恰群地层样品的古地磁测试和分析，获得可靠的高温特征剩磁分量，采用主成分分析该高温特征剩磁方向，建立该剖面高精度磁性地层年代学序列，与中新世国际标准极性柱对比获得该剖面时间跨度为~9.9-16.6 Ma。该剖面古水流方向均为较稳定的东西向水流，其与山脉平行，帕米尔东北缘-西南天山山脉处于较稳定的构造隆升期，表明帕米尔东北缘-西南天山南缘碰撞系碰撞对接时间早于~16.6 Ma。磁偏角统计发现无明显变化，表明此时两碰撞系汇聚作用较弱。另外，剖面上部的西域砾岩存在一生长地层，该生长地层表明西域砾岩的沉积是帕米尔东北缘-西南天山南缘碰撞系快速碰撞隆升的产物，据厚度推测其起始年代为~3 Ma。