HR: 16:20h
AN: T12F-11
TI: East-west variations in the crustal structure of the Southern Tibetan Plateau from magnetotelluric data
AU: * Unsworth, M
EM: unsworth@phys.UAlberta.ca
AF: University of Alberta, Institute for Geophysical Research, Edmonton, AB T6G 2JI Canada
AU: Wei, W
EM: wwb@cugb.edu.cn
AF: China University of Geoscience, Department of Applied Geophysics, 29, Xueyuan Road, Beijing, China
AU: Spratt, J
AU: Spratt, J
AF: Syracuse University, Department of Geological Sciences, Syracuse, NY 13244 United States
AU: Lin, C
AF: China University of Geoscience, Department of Applied Geophysics, 29, Xueyuan Road, Beijing, China
AU: Deng, M
AF: China University of Geoscience, Department of Applied Geophysics, 29, Xueyuan Road, Beijing, China
AU: Clarke, G
AF: University of Alberta, Institute for Geophysical Research, Edmonton, AB T6G 2JI Canada
AU: Jones, A
AU: Nelson, D
AF: Syracuse University, Department of Geological Sciences, Syracuse, NY 13244 United States
AU: Haines, S
AF: Stanford University, Dept. of Geophysics, Stanford, CA United States
AU: Jin, S
AF: China University of Geoscience, Department of Applied Geophysics, 29, Xueyuan Road, Beijing, China
AU: Yao, C
AF: China University of Geoscience, Department of Applied Geophysics, 29, Xueyuan Road, Beijing, China
AB: Magnetotelluric exploration during INDEPTH-II in 1995 revealed that the crust of the southern Tibetan Plateau is characterized by a high conductivity layer with it's top at a depth of 15-20 km. In combination with other geophysical and petrological data, the high conductivity has been attributed to a combination of saline fluids and partial melt. The 1995 magnetotelluric (MT) data were collected in the Yadong-Gulu rift system, and thus may not be representative of the entire east-west extent of the Tibetan Plateau. Additionally, the 1995 data did not image structure below the high conductivity layer, and thus cannot constrain the electrical structure of the lower crust and upper mantle beneath southern Tibet. To address these two questions, additional MT data were collected in Southern Tibet during May-September 2001. Broadband and long-period MT data were collected on two profiles in Southern Tibet. The first profile extended 250 km north-south at 92$^\circ$ E and traversed the Tethyan Himalaya and southern Lhasa Block. The second profile was located at approximately 85$^\circ$E. To obtain constraints on deeper electrical structure, very long period MT data were recorded at four stations on the 92$^\circ$ E profile. \par An initial two-dimensional inversion of the long-period MT data from 92$^\circ$ E show the following features: \begin{itemize} \item{Conductive mid-crustal layer beginning at a depth of 20-30 km beneath the Lhasa block. This terminates approximately 50 km south of the Yarlung-Zangbo suture. This is similar to the widespread conductor imaged on other INDEPTH magnetotelluric profiles throughout Tibet.} \item{A north dipping zone of enhanced conductivity that connects the mid-crustal conductor to the surface at approximately 28$^\circ$N.} \item{The dipping conductor is underlain by resistive unit from 28$^\circ$N to at least 28.5$^\circ$N (and perhaps further). This can be associated with the high Himalayan crystalline rocks and the underthrusting Indian Plate.} \end{itemize} \par The structure of the Tibetan crust at 92$^\circ$ E is broadly similar to that at 90$^\circ$E. This indicates that to first-order, the high conductivity layer is continuous east-west and not just a local expression of the Yadong-Gulu rift.
DE: 8045 Role of fluids
DE: 8102 Continental contractional orogenic belts
DE: 9320 Asia
SC: T
MN: 2001 AGU Fall Meeting