青藏高原东部地壳流可能分布范围的探讨

The Possible Distribution Range of Crustal Flow in the Eastern Tibetan Plateau

青藏高原拥有巨厚的地壳,在足够的温压条件下,其中、下地壳可能发生塑性变形,在地质时间尺度上表现为类似流体的运动,从而形成中下地壳流。诸多研究表明,地壳流在青藏高原内部可能大范围存在,并在高原演化过程中扮演着极为重要的角色,然而地壳流存在的范围、连通情况,及其是如何与其他构造作用一起调节青藏高原的动力学演化,还有待更深入研究。青藏高原东部是青藏高原向外扩展的前缘,对其现有的地球物理研究成果进行梳理,探讨地壳流分布特征,能够更好地讨论其在高原东向扩展中的作用,为进一步开展有针对性的地质和地球物理研究提供重要参考。本文以地震波速度结构探明的低速层分布为主要资料,同时综合电性结构和地震波各向异性特征,深入讨论了青藏高原东部地壳流可能的分布范围及其对高原演化的贡献,认为地壳流在青藏高原东南缘、东缘和东北缘具有不同的分布特点,且三个区域的变形特征存在显著差异性。

Tibetan Plateau,with its highest elevation and thickest crust,is the result from the convergence and collision between the Indian and Eurasian plates over the past 70-50 Ma.When the temperature and pressure are in a certain condition,the material of middle-lower crust can start to flow as crustal flow or lower-crust flow.Numerous studies have shown that crustal flow may exist on a large region within the Tibetan Plateau,and it should play an important role in the evolution of the plateau.However,it is still far to have a consensus on the extent and connectivity of crustal flow,and its interaction with other tectonic deformation processes to regulate the evolution of the Tibetan Plateau.Tibetan Plateau is expanding along its eastern margin,hence it is necessary to make a summary review of all available geophysical results at eastern Tibet,and then discuss the distribution of crustal flow and its contribution to the evolution,which may provide good guidance for geological and geophysical studies in the future.In this paper,we summarized the distribution of the low-velocity zone in middle-lower crust based on different seismological studies.Combined with the results from magnetotelluric and seismic anisotropy analysis,we discussed the extent and scale of crustal flow in the eastern Tibetan Plateau,and its contribution to the evolution of the plateau.We suggested that the crustal flow has various distribution characteristics among the southeastern margin,eastern margin and northeastern margin of the Tibetan Plateau,where the deformation pattern is significantly different.