Abstract: Based on deep geophysical data,the geodynamic features of the upper mantle and possible driving mechanism are dicussed through a description of the basic structure of the upper mantle in the Tianshan seismic belt. It is supposed that horizontal squeezing deformation is one of main causes to make the upper mantle lithosphere shortened and thickened in the western Tianshan and the southern Tianshan adjacent to the western Kunlun; whereas in the central Tianshan and parts of the eastern Tianshan next to the southern edge of the Zhungeer basin,besides horizontal squeezing force caused by the plate movement,hot materials in the upper mantle perhaps flow upward to uppermost mantle,even intrude into the lower crust. As horizontal movement,they will influence the teconic activity of brittle medium in crust,in particular,a detachment layer with low velocity near the Moho under lower crust has become an important feature of the deep tectonics of the seismic region. In addition,since the India-Asia continental collision,the cool and solid root in parts of the Tianshan probably departed from original position and fell into upper mantle due to multiple squeezing deformation and thermal convection of small scales.

Key words: Tianshan, Upper mantle, Tectonic movement, Deep structure, Low-velocity zone

摘要： 以深部地球物理资料为基础,介绍了天山地震带上地幔的基本结构,讨论了天山不同地区上地幔介质的动力学性质和可能的驱动机制。认为水平挤压形变是造成西天山和天山毗邻西昆仑附近区域上地幔岩石圈缩短和增厚的主要原因;而在中天山和东天山靠近准噶尔盆地南缘一带,除了板块运动造成的水平挤压力之外,上地幔热物质有可能上浮甚至侵入到地壳之中。它们与水平运动一样,对壳内脆性介质的构造活动起到非常重要的作用,特别是地壳底部莫霍面附近的低速滑脱层成为震源区深部构造的一个明显标志。此外,自从印度 亚洲大陆碰撞以来,天山部分地区固结冷却的山根有可能在多重挤压变形和小尺度热对流的共同作用下,脱离它们的原有的层位而沉入上地幔。

关键词: 天山, 上地幔, 构造运动, 深部构造, 低波速带