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Origin of the high conductivity anomalies in the mid-lower crust of the Tibetan Plateau: Dehydration melting of garnet amphibolites
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  • Xinzhuan Guo,
  • Sibo Chen,
  • Chao Zhang,
  • Yao Wu,
  • Xiong Wang,
  • yanfei zhang,
  • Xiang Wu,
  • Junfeng Zhang
Xinzhuan Guo
Chinese Academy of Sciences

Corresponding Author:[email protected]

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Sibo Chen
Stonybrook University
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Chao Zhang
China University of Geosciences (Wuhan)
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Yao Wu
State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences
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Xiong Wang
China University of Geosciences
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yanfei zhang
Hohai University
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Xiang Wu
China University of Geosciences
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Junfeng Zhang
China University of Geosciences (Wuhan)
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Abstract

High-conductivity anomalies of 0.1–1 S/m are widely distributed in the mid-lower crust of the Tibetan Plateau. Dehydration of amphibole-bearing rocks may play an important role in explaining these anomalies. To survey the anomalies’ origin, therefore, the electrical conductivities of amphibole-bearing samples, containing varying amphibole content, are measured at 1.5 GPa and 600–1300 K. Our experiments show that dehydration melting occurs at about 1100 K. Proton conduction and ionic conduction dominate the conduction mechanisms before and after dehydration melting, respectively. The dehydration melting of felsic rocks, containing 25 vol% of amphibole, is unable to account for the high-conductivity anomalies of 0.1–1 S/m. In contrast, the dehydration melting of garnet amphibolite, with an amphibole content higher than 60 wt%, can enhance the bulk conductivity to higher than 0.1 S/m under the lower-crust conditions beneath the Tibetan Plateau. The melt fraction of the garnet-amphibolite is estimated to be 3.8–36 vol% in the partial molten region based on a cube-model simulation.