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《Acta Geologica Sinica》 2004-02
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East-West Segmentation of the Tibetan Plateau and Its Implication

ZHANG Jin, MA Zongjin School of Earth and Space Sciences, Peking University, Beijing, 100871  
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.
【Fund】: 国家自然科学基金(编号4983402)
【CateGory Index】: P542.2
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