THE CAUSE OF FORMATION OF THE LAYERS WITH LOW VELOCITY AND HIGH ELECTRICAL CONDUCTIVITY IN WESTERN TIBET

Comprehensive geophysical survey carried out in Western Tibet discovered that there is a layer with low velocity and high electrical conductivity embedded in the depth of 10～25km with a thickness of n km beneath the southern Gandise terrain and the southern Qiangtang terrain respectively. A low velocity body, simultaneously a high electrical conductivity body, exists in the depth of 40km with a thickness of 11～22km, expanding about 100km in NS direction beneath Dongco basin in the northern Gandise.In order to investigate how these layers were formed, more study on deep thermal status is needed.There is neither heat flow values measured on the spot nor thermal parameters measured of the typical rock in Western Tibet. The relations between heat flow values and other geological and geophysical parameters are analyzed. A method to calculate heat flow values and temperature distribution with the depth using the depth of Moho and the depth of the asthenosphere is suggested. In the area where there are both heat flow values measured and the two depths mentioned above, the heat flow values calculated using this method are very similar to the heat flow values measured.