中文摘要：

基于Airy地壳均衡理论，计算了川西地域（28°～32°N，99°～105°E的范围内）的理论均衡地壳厚度，并与由实际重力资料反演得到的地壳厚度进行对比，从而得到了该区的地壳均衡状态。经过分析研究发现以龙门山、鲜水河、安宁河三大断裂系所组构的“Y”形构造系为界，可将研究区的均衡状态分为东、中、西三部分，对应着3种不同类型的均衡状态：在“Y”形构造系以东的四川盆地内部，理论地壳厚度与实际地壳厚度的差异值△I接近于零，即地壳处于较均衡稳定的状态；在“Y”形构造系以西的巴颜喀拉块体地域，△I均可达到-8km左右，个别地域甚至最高可达-13km，说明该区地壳处于强烈的负均衡异常状态；而在研究区中部的“Y”形构造系部位，主要表现为较复杂的正负相问的均衡异常状态。在此基础上，也对该区产生现今这样复杂而特异的均衡异常格局的动力学机制进行了探讨研究，认为其主要应归结于青藏高原深部壳、幔物质在印度板块与欧亚板块的碰撞下发生的东向流展并在川西地域受到坚硬的四川盆地的阻隔而被迫转向东南，在此过程中导致地壳物质堆积，从而造成了该区复杂而特异的地壳均衡异常格局。

英文摘要：

In this study,the theoretical isostatic thickness of the crust in Western Sichuan（28°- 32°N,99°- 105°E）was calculated according to the Airy crustal isostatic theory. The crustal isostatic state of this area was obtained by comparing the theoretical crustal isostatic thickness with the crustal thickness inversed from the observed gravity data. It was found that the study area could be divided into three parts by the ＂ Y＂ shaped tectonic system consisting of the Longmenshan fault,the Xianshuihe fault,and the Anninghe fault. The three parts correspond to the three isostatic states. In the Sichuan Basin east of the ＂Y＂ shaped tectonic system,the difference between measured and theoretical isostatic crust thickness,AI,is close to zero,which means the crust in this area is in an isostatic and stable state. In the Bayankala block west of the ＂Y＂ shaped tectonic system, the average AI is about-8km,which means the crust in this area is in a obviously negative isostatic anomaly state. In the ＂Y＂ shaped tectonic system, the crust isostatic state is in a special state of alternative positive and negative anomalies. Such a distribution pattern of the crustal isostatic states in the study area can be attributed to the following process： with the collision between Indian and Eurasian plates, the deep materials beneath the Tibet plateau have flowed eastward, but because of the resistance of the rigid Sichuan Basin,they have been forced to flow southeastward. During this process, the crustal materials accumulated and resulted in such a complicated and special crustal isostatic state.