Crustal rheology of the Himalaya and Southern Tibet inferred from magnetotelluric data

Abstract

The Cenozoic collision between the Indian and Asian continents formed the Tibetan plateau, beginning about 70 million years ago. Since this time, at least 1,400 km of convergence has been accommodated1 by a combination of underthrusting of Indian2 and Asian lithosphere, crustal shortening3, horizontal extrusion4 and lithospheric delamination5. Rocks exposed in the Himalaya show evidence of crustal melting1,6 and are thought to have been exhumed by rapid erosion and climatically forced crustal flow7,8. Magnetotelluric data can be used to image subsurface electrical resistivity, a parameter sensitive to the presence of interconnected fluids in the host rock matrix, even at low volume fractions. Here we present magnetotelluric data from the Tibetan–Himalayan orogen from 77° E to 92° E, which show that low resistivity, interpreted as a partially molten layer, is present along at least 1,000 km of the southern margin of the Tibetan plateau. The inferred low viscosity of this layer is consistent with the development of climatically forced crustal flow in Southern Tibet.

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Figure 1: Map of the Tibetan plateau showing the location of the MT profiles.
Figure 2: Resistivity models for the four profiles derived from inversions of the MT data.
Figure 3: Comparison of 100-line resistivity model and the INDEPTH common mid-point reflection profile. B1 and B2 are seismic bright spots that indicate zones with high fluid content.
Figure 4: Summary of laboratory measurements of the electrical resistivity and mechanical properties of a partially molten rock.

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Acknowledgements

The MT data were collected and analysed with support from the US National Science Foundation, the Ministry of Land and Resources of China, the Ministry of Education of China, the National Science Foundation of China, NSERC (Canada) and the Alberta Ingenuity Fund. Data in India were collected with funding from the ESS Division, Department of Science and Technology, Government of India, under the Deep Continental Studies Program. Data acquisition in Nepal was supported by CNRS-INSU and by the French-Nepalese cooperation agreement. Discussions with M. Edwards, W. Kidd and D. Nelson are acknowledged. We dedicate this paper to the memory of Doug Nelson, who inspired us all.

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Correspondence to M. J. Unsworth.

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Supplementary information

Supplementary Figure 1

Detailed map of Southern Tibet showing the location of three INDEPTH MT profiles. Numbers refer to MT sites shown in Figure S2. ITS = Indus-Tsangpo suture. YGR = Yadong Gulu Rift. (PDF 5485 kb)

Supplementary Figure 2

This gives details of the fit of the MT data to the predicted fit of the models shown in Figure 2 of the main Letter. (PDF 252 kb)

Supplementary Figures Legends

This file contains captions for the two Supplementary Figures. (DOC 339 kb)

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Unsworth, M., Jones, A., Wei, W. et al. Crustal rheology of the Himalaya and Southern Tibet inferred from magnetotelluric data. Nature 438, 78–81 (2005) doi:10.1038/nature04154

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