摘要
青藏高原东北缘处于青藏高原向中国大陆内部扩展的前缘部位,其地质构造复杂,岩石圈变形样式丰富,是探索大陆内部岩石圈构造变形与深部过程的天然实验室。半个多世纪以来,该地区已开展了多期次以揭示壳、幔深部结构为目标的地球物理探测,通过收集前人的研究成果,对青藏高原东北缘的壳、幔深部结构研究进展以及存在的问题作了简要介绍和初步讨论。国内外最新研究成果表明:1)青藏高原东北缘地壳较厚,但普遍缺失高速铁镁质下地壳,其低泊松比属性预示该地区下地壳流不发育;2)高原东北缘大部分区域保留有较厚的岩石圈,且上地幔各向异性快轴方向与地表构造走向基本一致,表明该地区壳、幔耦合变形可能性较大;3)昆仑断层南北两侧壳、幔深部结构存在较大差异,预示其是上地幔变形的转换带。
The northeastern Tibetan plateau is the transition zone from Tibet to the Chinese mainland interiors.The complex tectonics and lithospheric deformation in study area provide a natural laboratory for exploring the lithospheric deformation and deep processes of the intra-continent. Over the past half a century,a range of geophysical surveys have been conducted for studying the deep structure of the northeastern Tibetan plateau. In this paper,these previous studies are reviewed and some controversial issues are discussed. The contents include. 1) The crust of northeastern Tibet has been thickened,but the mafic lower crustal layer is missing,and the low Poisson's ratio suggests no lower crustal flow existing throughout the studying area. 2) The lithosphere beneath the northeastern Tiber is thick,and the anisotropic fast-axis direction is consistent with the surface tectonic trends,which indicate a coherent deformation throughout the crust and the upper mantle. 3) The crustal and upper mantle structure,south of the Kunlun fault,is different from that of north fault,which indicate that the Kunlun fault may be an upper-mantle deformation transition zone.