【摘要】 经过近几十年的研究,人们已经普遍认为青藏高原是由几条近东西向的块体先后拼贴而成,大型的东西向构造是高原内部最明显的构造特征。然而根据最近所获得的有关西藏高原以及附近地区的重力场、地震层析成像、地震活动性、水平位移速度场以及地质等资料,发现整个西藏高原内部存在着明显的两条重要的南北向或近南北向构造和一些小型的南北向构造,它们将西藏高原划分为西、中、东三个有各自构造特点的部分;西侧的南北向构造沿84°～85°E延伸,东侧的近南北向构造位于92°～94°E之间。这两个构造带在上述的多种地球物理资料中均有良好的显示,是重要的重力异常变异带、重要的热结构边界带、重要的地震活动带,也是明显的地貌陡变带,等等。高原西部地形崎岖,剥蚀最深,布格重力异常最高,目前向北北西方向运动;中部地区地表平坦,发育众多的南北向地堑裂谷,东西向伸展活动最明显,海拔最高,集中分布了7座超过8000m的高峰,目前向北东东方向运动;而东部地区地形也比较崎岖,发育许多目前仍在强烈活动的走滑断层,在这些断层之间,地块相对转动,目前向北东甚至南东方向运动。造成西藏高原东西分段的原因现在还不清楚,笔者等倾向认为造成这种现象可能是由于与欧亚板块发生碰撞的印度板块在横向上也是西、中、东分段的,印度更多还原

【Abstract】 After more than 30 years’ research, people have already know that the Tibetan Plateau is formed by several east—west-trending blocks (Lhasa Block, Qiangtang Block, etc. ) colliding with each other during the last tens of million years. However, with many interdisciplinary projects carried out in the Tibetan Plateau and surrounding areas, we find that there are at least two large nearly north—south trending tectonic zones developed in the interior of the Tibetan Plateau, which cut the Plateau into three parts from west to east. These three parts are different in topography, movement direction of crust, Bouguer gravity anomaly, structures in the depth, thickness of the crust and lithosphere, and many other geological characteristics. The Bouguer gravity anomaly is the highest in the western part, and the present crust movement there is directing to the northern northwest, which is different from the other two parts. The central part is a special area and there are many characteristics that can distinguish it from other two parts. There are seven larger north—south-trending rifts and many small east—west extensional faults and glaciers developed in the central part. Most summits over 8000 m above sea level along the Himalayas are located in the central part. Moreover, the movement direction of this part is northern northeast, and most Cenozoic volcanoes also distribute in the central part. In the eastern part, there are several large strike-slip faults cutting into several smaller blocks, which rotate clockwise, so, the movement direction of the crust is also clockwise, from northeast to east. The western boundary (84°E~85° E) between the west part and the central part is tracing one seismic zone (Lazhulong—Amuzhong) that was recently found. The movements across this zone calculated by focal mechanics show transtension between these two parts. The eastern boundary (92°E~94°E) is tracing another large seismic zone (Yadong—Amdo) in the interior of the plateau, which is more than 1000 kilometers long. This seismic zone goes through the Himalayas to India. A largest rift zone (Yadong—Amdo) in the Tibetan Plateau also extends along this boundary. From many CT profiles going through the plateau at the different depth, we can also find that the boundaries between the units can go down for about four hundred kilometers to the upper mantle. These may result from the inhomogenous Indian Plate, which is colliding with the Eurasian Plate. It is the segmented Indian Plate that leads to the different deformations and crust movements between the three parts.更多还原