藏北羌塘地区的地壳电性结构及其意义

羌塘地区地壳的电性层可分为上、中、下 3层。中电性层为一连续的低阻层 ,厚度平均 2 0km左右。上、下电性层块断作用强烈 ,而中电性层韧性好 ,表现为褶皱弯曲。如果上层高阻高密体发育 ,则中层顶界面埋深增大 ;如果下层高阻层发育 ,则中层的顶界面抬升。中电性层在北羌塘平缓 ,厚度均匀 ;而在南羌塘此层连续性较差 ,埋藏深。壳幔层对下地壳与中地壳的增厚起制约作用 ,而中地壳对上地壳的增厚起调节作用 ,不同规模的断裂又是各层增厚不可缺的条件。

ELECTRICAL STRUCTURE OF CRUST IN THE QIANGTANG REGION, NORTHERN TIBET AND ITS GEOLOGICAL SIGNIFICANCE

The crust of the Qiangtang region in northern Tibet could be divided into three parts, i.e., the upper, middle and lower ones, as shown by magnetotelluric sounding prospecting results. The continuous middle part is about 20km thick, showing lower electric resistance, good tenacity and more foldings; while the upper and lower ones are more brittle, consisting of many more fault blocks. Among the three parts, a good corresponding relation has been recognized, that is, if the resistance and density of the geological bodies in the upper part both are high, the depth of the middle part is deep; if there are more resistance bodies in the lower part, the top boundary of the middle part will rise. The thickness of the middle one is nearly constant at northern Qiangtang; whereas at southern Qiangtang the depth of the middle part is deeper, and with poor consistence. The crust-mantle mixed layer could restrict the thickening of the middle and lower crusts; while the middle crust could adjust the thickness of the upper crust. Faults with different dimension are necessary for the thickening of the three parts.