Detection of widespread fluids in the Tibetan crust by magnetotelluric studies

Magnetotelluric exploration has shown that the middle and lower crust is an omalously conductive across most of the north-to-south width of the Tibetan plateau. The integrated conductivity (conductance) of the Tibetan crust ra nges from 3000 to greater than 20,000 siemens. In contrast, stable continen tal regions typically exhibit conductances from 20 to 1000 siemens, averagi ng 100 siemens. Such pervasively high conductance suggests that partial mel t and/or aqueous fluids are widespread within the Tibetan crust. In souther n Tibet, the high-conductivity layer is at a depth of 15 to 20 kilometers a nd is probably due to partial melt and aqueous fluids in the crust. In nort hern Tibet, the conductive layer is at 30 to 40 kilometers and is due to pa rtial melting. Zones of fluid may represent weaker areas that could accommo date deformation a nd lower crustal flow.