CONDUCTIVITY STRUCTURE OF THE BANGONG SUTURE ZONE, 
CENTRAL TIBET, FROM INDEPTH-III MAGNETOTELLURIC DATA

Kurt D. Solon(1), A.G. Jones(2), K.D. Nelson(1), M.J. Unsworth(3)
(1) Department of Earth Sciences 
    204 Heroy Geology Laboratory 
    Syracuse University 
    Syracuse, New York 13244, USA 
(2) Geological Survey of Canada
    615 Booth Street, Room 218
    Ottawa, Ontario, K1A 0E9 Canada
(3) University of Washington Geophysics Program 
    Box 351650, Seattle, WA 98195-1650, USA
kdsolon@syr.edu

As part of the collaborative and ongoing efforts of project INDEPTH, 
both broadband and long period magnetotelluric data were collected 
from July to August 1998 along a 400 km north-south profile in central 
Tibet.  The profile crosses the Bangong Suture, which is the principal 
terrane boundary within the central Tibetan Plateau and coincides with 
marked south-to-north changes in the seismological properties of the 
plateau lithosphere. Tensor distortion analyses were applied to the MT 
data from the sites around the suture in order to determine 
dimentionality and derive regional geoelectric strike direction and 
regional MT response functions.  These analyses suggest that the 
regional electrical structure is two-dimensional to periods of 
5,000 seconds, with a strike direction of 095.  This strike direction 
corresponds well with the surficial geological strike in this region.  
Two-dimensional inversions, Mackie 2D, of the MT data show the 
following first-order features.  1 The regional midcrustal conductor 
sensed previously in the southern Tibetan Plateau continues into the 
central plateau, with its top at depths of 15-20 km beneath the suture 
zone.  2 The Bangong Suture coincides with a 40 km wide, sub-vertical, 
conductive zone/s  which extends upward from the regional midcrustal 
conductor to the near surface.  This zone of conductivity is spatially 
coincident with a measured low seismic velocity zone, mapped 
strike-slip faults as well as geothermal activity.  3 Deeper in the 
crust, beneath the suture, a very conductive zone is sensed at depth 
of 30-40  km.