| Abstract: | Geoelectrical investigations in Tibetan Plateau show that there are two high conductivity layers (HCLs) in the crust of southern Tibetan Plateau. The first HCL is at a depth of 15～20km, and the second at 45～60km. In the central region of the Plateau, such as north Qiangtang and Bayan Har, there is only one HCL in crust at the depth about 15～20km.The origin of HCL in upper crust of southern Tibet is mainly caused by free saline aqueous fluids. The seismic investigation by project INDEPTH in southern Tibet demonstrates that the bright spot reflection at about 15km depth is caused by 10% volume of free aqueous fluids (Makovsky and Klemperer, 1999). Seismic and heat flow research indicates the temperature in 15km depth of Tibet is from 400℃ to 650℃. The high concentration of Cl - in water of geothermal spring in southern Tibet means that the aqueous fluid in crust is saline water. The experiment on conductivity of NaCl solution shows that the conductivity is more than 4.5 S·m -1 under 400MPa and 300～650℃ condition (Quist and Marshall, 1968). This p\|T condition corresponds to the pressure and temperature range at 15～20km depth of Tibet. |
