HR: 14:15h
AN: T32E-04
TI: Crustal and upper mantle structure beneath Northern Tibet and the Kunlun Shan : initial results of 1999 INDEPTH MT fieldwork
AU: * Unsworth, M J
EM: unsworth@geophys.washington.edu
AF: University of Washington, Geophysics Program Box 351650, Seattle, WA 98195 United States
AU: Li, S
AF: University of Washington, Geophysics Program Box 351650, Seattle, WA 98195 United States
AU: Bedrosian, P
AF: University of Washington, Geophysics Program Box 351650, Seattle, WA 98195 United States
AU: Booker, J R
AF: Chinese University of Geosciences, Dept. of Applied Geophysics,29, Xueyuan Road, Beijing, 100083 China
AU: Wei, W
AF: Chinese University of Geosciences, Dept. of Applied Geophysics,29, Xueyuan Road, Beijing, 100083 China
AU: Tan, H
EM: thd@cugb.edu.cn
AF: Chinese University of Geosciences, Dept. of Applied Geophysics,29, Xueyuan Road, Beijing, 100083 China
AU: Jin, S
AF: Chinese University of Geosciences, Dept. of Applied Geophysics,29, Xueyuan Road, Beijing, 100083 China
AU: Deng, M
AF: Chinese University of Geosciences, Dept. of Applied Geophysics,29, Xueyuan Road, Beijing, 100083 China
AU: Jones, A G
EM: ajones@cg.nrcan.gc.ca
AF: Geological Survey of Canada, 615 Booth Street, Ottawa, ON Canada
AB: INDEPTH magnetotelluric (MT) exploration in Southern and Central Tibet in 1995 and 1998 detected an extensive mid-crustal layer of anomalously low resistivity that was present both inside and outside the Yadong-Gulu rift system. This zone is may be due to either saline fluids, interconnected partial melt. In April-June 1999 this study was extended to cover the Northern part of the Tibetan plateau where competing models for the formation of the Tibetan plateau predict very different crustal and mantle structure. Long period MT data were collected at 25 sites on the Lhasa-Golmud highway from Tangula Shan to the Quaidam Basin. These data have been inverted to generate an electrical resistivity model of the crust and mantle beneath the northern margin of the plateau. The principal features of the model are:- \begin{itemize} \item{1. The mid-crustal conductive layer extends beneath the entire Qiangtang terrane and across the Jinsha suture into the Songpan Ganz terrane with a conductance $\sim$ 4000 S. It terminates south of the Kunlun Fault.} \item{2. A zone of extremely low resistivity is imaged in the crust and upper mantle, centered just south of Toutouhe at 34$^\circ$ north. The conductance of this layer is in excess of 10,000 S and is most probably due to partial melt. The zone may have been produced by the asthenospheric upwelling that may have resulted in crustal delamination as the plateau formed.} \item{3. The Kunlun Shan is characterized by a resistive crust that is bounded by sediment filled basins on both the north and south. The data suggest that the resistive zone beneath the Kunlun Shan may dip southward.} \end{itemize}
DE: 8015 Local crustal structure
DE: 8045 Role of fluids
DE: 8102 Continental contractional orogenic belts
DE: 8110 Continental tectonics--general (0905)
SC: T
MN: 1999 AGU Fall Meeting