Publication 127
Conductivity structure and rheological property of Lithosphere in Southern Tibet
inferred from super-broadband magnetotelluric sounding
WEI WenBo, JIN Sheng, YE Gaofeng, DENG Ming, JING Jian’Enn, Martyn UNSWORTH, Alan G. JONES
Abstract
To understand deep lithosphere structure beneath the Qinghai-Tibet Plateau more comprehensively and objectively and to explore
important scientific issues, such as characteristics of plateau lithospheric deformation, state of strain, thermal structure,
plate (or terrane) movement, crust-mantle rheology, it is necessary to research the varieties of crust-mantle electrical structure
in the east-west direction in geological structures of the plate. For this purpose, six super-broadband magnetotelluric (MT)
sounding profiles have been completed by INDEPTH-MT Project in the Himalayas-Southern Tibet. Based on the imaging results
from the six profiles, three-dimensional electrical conductivity structure of the crust and upper mantle has been analyzed
for the research area. The result shows that the high-conductivity layers in the middle and lower crust exist widely in Southern
Tibet, which extend discontinuously for more than 1000 km in the east-west direction and become thinner, shallower and more
resistive toward the big turning of the Yarlung Zangbo River. The discussion on the rheology of lithosphere in Southern Tibet
suggests that the middle-lower crust there has a high electrical conductivity, implying the existence of “partial-melt” and “hot
fluid” in the thick crust of Tibet, which make the medium hot, soft, and plastic, or even able to flow. Combining the experimental
result of petrophysics and the MT data, we estimate the melting percentage of the crustal material to be up to 5%-14%,
which would reduce the viscosity of aplite in the crust to meet the flow condition; but for granite, it is likely not enough to
cause such a change in rheology.
Source
Science in China Series D: Earth Sciences, 53, 1–14.
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Alan G Jones / 28 July 2010 /
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