Publication 103
Structure of the crust in the vicinity of the Banggong-Nujiang suture central Tibet
from INDEPTH magnetotelluric data
Solon, K., A.G. Jones, K.D. Nelson, M.J. Unsworth, W. Wei, H. Tan, H., S. Jin, M.Deng,
J.R. Booker, S. Li, P. Bedrosian
Abstract
Magnetotelluric data from a 150-km-long profile crossing the Banggong-Nujiang
suture (BNS), central Tibet, acquired as part of the International Deep Profiling of
Tibet and the Himalaya (INDEPTH) project, have been examined for crustal and upper
mantle structure. Strike and dimensionality analyses demonstrate that regional-scale
electrical structures are two-dimensional and oriented approximately parallel to surface
geological strike. As seen elsewhere in Tibet, the double thickness crust is generally
characterized by resistive upper crust (hundreds to thousands of ohm meters) overlying
conductive middle and lower crust (tens to hundreds of ohm meters), but in detail, there
are lateral variations at all levels. Regionally, a northward transition from thick (>45 km)
to thin (<15 km) resistive upper crust coincides with (1) the surface trace of the BNS,
(2) a prominent strand of the Karakorum-Jiali fault system, (3) northward decrease in
upper mantle seismic velocities and increase in attenuation, and (4) pronounced northward
onset of seismic polarization anisotropy. The latter two seismological features have been
taken to mark the northern limit of Indian mantle lithosphere thrust beneath southern
Tibet. On the basis of our electrical model, we speculate that (1) the resistive upper
crustal root beneath the Neogene Lunpola and Duba basins was produced by crustal
shortening localized along the northern edge of the Lhasa terrane; (2) the low midcrustal
resistivity beneath the BNS reflects enhanced Neogene melting and/or metamorphic
dewatering of relatively fertile subduction zone complex rocks; (3) observed steep upper
crustal low-resistivity anomalies are produced by hydrothermal fluids within active
faults localized within and adjacent to the BNS; and (4) these strike-slip and extensional
fault arrays are surface manifestations of lithosphere-penetrating shear localized along
the northern edge of the underthrust Indian plate.
Source
<Journal of Geophysical Research, 110, B10102, doi: 10.1029/2003JB002405, 2005.
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Alan G Jones / 21 April 2006 /
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