北祁连—阿拉善地块南缘的地壳精细结构及古生代构造对新生代青藏高原向北扩展的约束

North Qilian Orogen-Hexi Corridor - the southern margin of the Alashan block (SAB) is located on the northern margin of the Qinghai-Tibet Plateau. It is the key region to studying the the uplift and the northward propagation of the plateau, and understanding the ongoing collision between India and Eurasia. The northern Qilian, as a Paleozoic orogen as well, has experienced a complete "trench-arc-basin" system, and preserved the Paleozoic framework well. Since the Cenozoic, the collision between India and Eurasia has led to the uplift and outward growth of the northern margin of the Qinghai-Tibet Plateau. The Cenozoic igneous rocks, which is not developed in the north Qilian and the region to the north, reflects the constraint of the Paleozoic framework of the North Qilian and the peripheral to the northward propagation of the plateau in Cenozoic. In this proposal, we are intending to be based on the deep seismic reflection and wide-angle reflection & refraction data collected from the North Qilian-Hexi Corridor-the SAB, then via the joint processing and interpretation to obtain the whole detailed crust structure. Then an alternative quantitative approach for distinguishing among plateau construction models is going to be used to evaluate the spatial and temporal variations in the magnitude and style of Cenozoic crustal shortening strain via balanced cross-section construction and restoration. Then we will figure out the model of the uplift and the northward propagation will be revealed. The deep geophysical data, combining with the other data will reveal the subduction polarity of the North Qilian Ocean in early Paleozoic and evolution history of the Qilian orogenic belt. Ultimately, the constraints of the Paleozoic framework of the Qilian orogen and peripheral tectonic units to the uplift and outward propagation of the Qinghai - Tibet Plateau in Cenozoic will be unfolded.

北祁连-河西走廊--阿拉善地块南缘位于青藏高原北缘，是研究高原隆升和北缘向北扩展，理解进行中的印度与欧亚大陆碰撞的大陆动力学的关键部位。同时，北祁连作为古生代缝合带，经历了完整的“沟弧盆”体系，并完好的保留了古生代的构造特征。新生代以来印度和欧亚两大板块碰撞挤压导致了青藏高原北缘的隆升和向外扩展。北祁连及其以北未发育新生代的岩浆，反映了北祁连及周缘古生代构造对新生代高原向北扩展的约束作用。本项目拟以穿越北祁连-河西走廊-阿拉善地块南缘联合采集的深地震反射和宽角反射与折射数据为基础资料，进行约束处理解释，获得北祁连-阿拉善地块南缘的全地壳精细结构。并进行平衡剖面构建和恢复，定量化揭示青藏高原北缘的缩短量，揭示其隆升机制和向北扩展的行为方式；通过深部地球物理数据和其他数据揭示北祁连洋早古生代的俯冲极性和祁连造山带古生代构造演化，揭示祁连山古生代构造对新生代青藏高原隆升和向外扩展的约束。

新生代以来，欧亚与印度两大板块间的碰撞拼合及后续的汇聚挤压塑造了现今青藏高原的高海拔地形地貌和巨厚地壳。北祁连-河西走廊--阿拉善地块南缘位于青藏高原最北缘及其以北地区，其内部构造变形的几何学和运动学特征记录了地球最新演化历史过程中，构造、剥蚀和气候变化之间的复杂关系，是研究高原隆升和北缘向北扩展，理解进行中的印度与欧亚大陆碰撞的大陆动力学的关键部位。同时，北祁连作为古生代缝合带，经历了完整的“沟弧盆”体系，并完好的保留了古生代的构造特征。新生代以来印度和欧亚两大板块碰撞挤压导致了青藏高原北缘的隆升和向外扩展。北祁连及其以北未发育新生代的岩浆，反映了北祁连及周缘古生代构造对新生代高原向北扩展的约束作用。项目研究过程中，我们以穿越北祁连-河西走廊-阿拉善地块南缘联合采集的200km长的深地震反射和450km长的宽角反射与折射数据为基础资料，通过联合处理解释，获得了北祁连-阿拉善地块南缘的全地壳精细结构。结果显示研究区莫霍面整体由阿拉善地块南缘向南加深，由42-48 km加深48-54 km，同时在走廊盆地之下有一条明显北倾的地幔反射体，同时，宽角反射&折射地震剖面显示在河西走廊盆地之下有明显异于两侧的加厚的壳幔过渡带，可能代表了早古生代祁连洋闭合的地幔板片残留。结合其他地质地球物理资料，我们认为这揭示了北祁连洋早古生代向北的俯冲极性；深反射和地表层析速度成像结果显示北祁连下方存在明显的反射透明区、高速异常体，结合地表地质调查，推测其可能为花岗岩体，且其隆升受控于两条背向逆冲断裂带的控制。在祁连山下方上下地壳解耦，但不是以一条简单的连续发育的滑脱面为解耦面，而是后期发育的滑脱面截切了早期发育的滑脱面，并控制了祁连山新生代以来以分散缩短机制持续向外扩展，并使河西走廊盆地和阿拉善南缘逐渐成为青藏高原的新的组成部分。