东喜马拉雅构造结东缘地壳物质流的连续性研究

Collision of Indian plate with Eurasian plate created the growing of the Himalaya and Tibetan plateau.The deformation mechanism of the lithosphere is one of the key for understanding the growth of the plateau.GPS studies show that the surface motion has been going on in a clockwise rotation around the Eastern Himalayan Syntaxis(EHS),while the knowledge of the deep backgound associated with the rotation is still poor.In the Phase I of the EHS3D project,two low resistivity anormalous channels,which were inferred to as the crustal flows in the mid-lower crust around the EHS, have been defined by MT+LMT measurements.But due to the large space between the lines, the continuity of the flow can not be confirmed by the present data. Additionally, seismic sduties show a Low velocity zone(LVZ) in the north and northeast of EHS that is coincident with our MT results.But the LVZ goes to disappear in the west of Yunan. And the SKS fast direction of the same data indicated that the mantle flow changes its direction from NS to WE in the same area. This seems to imply the discontinuity of the crustal flow around the EHS.This project is to conduct MT+LMT measuremtns along two lines to exam the above point. One line (EHS3D-6) goes WE between the EHS3D-1 and the CZMT-WE,the other(EHS3D-8) lays NS crossing the EHS3D-6 in the middle.The fluidity and continuity of the crustal materials are significant to the study of the mechanism of growth of the Tibetan plateau.

岩石圈的变形方式是研究青藏高原生长动力学机制中的关键问题之一。GPS观测发现青藏高原东部环绕东构造结作顺时针旋转运动，但人们对其深部机制了解不够。EHS3D项目第一阶段的研究结果揭示出青藏高原东部存在两条环绕东构造结的中下地壳物质流,由于原来测线之间距离太大，不能确认上述地壳流在滇西地区是否连续分布。地震层析成像研究表明上述地区中地壳存在低速层，但在滇西地区不连续，同一资料的SKS快方向在东构造结北缘和东北缘与地面运动方向基本一致，而在滇西地区突然发生了近90度的转折，也预示了地幔流的不连续性。因此，本项目提出在EHS3D项目第一阶段工作的基础上，在EHS3D-1和CZMT-WE测线之间增加一条东西向和南北向的MT+LMT测线，求证地壳流在滇西地区是否连续分布。地壳流是关于青藏高原生长机制的一种新观点，地壳物质的流动性和连续性是检验该模型是否成立的重要指标。

岩石圈的变形方式是研究青藏高原生长动力学机制中的关键问题之一。GPS观测发现青藏高原东部环绕东构造结作顺时针旋转运动，但人们对其深部机制了解不够。EHS3D项目第一阶段的研究结果揭示出青藏高原东部存在两条环绕东构造结的中下地壳物质流,由于原来测线之间距离太大，不能确认上述地壳流在滇西地区是否连续分布。地震层析成像研究表明上述地区中地壳存在低速层，但在滇西地区不连续，同一资料的SKS快方向在东构造结北缘和东北缘与地面运动方向基本一致，而在滇西地区突然发生了近90度的转折，也预示了地幔流的不连续性。因此，本项目在EHS3D项目第一阶段工作的基础上，在EHS3D-1和CZMT-WE测线之间增加一条东西向和南北向的MT+LMT测线，求证地壳流在滇西地区是否连续分布。目前，该项目的野外观测已经完成，初步成果显示出，滇西地区的岩石圈结构具有很强的不均匀性和各向异性，地壳流的分布具有网络状或串珠状的特点，深大断裂对地壳流的分布具有强烈的控制作用，但在大范围区域分布上具有连续性。