Lower-crustal earthquakes in southern Tibet are linked to eclogitization of dry metastable granulite

Feng Shi, Yanbin Wang (), Tony Yu, Lupei Zhu, Junfeng Zhang, Jianguo Wen, Julien Gasc, Sarah Incel, Alexandre Schubnel, Ziyu Li, Tao Chen, Wenlong Liu, Vitali Prakapenka and Zhenmin Jin
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Feng Shi: China University of Geosciences
Yanbin Wang: The University of Chicago
Tony Yu: The University of Chicago
Lupei Zhu: Saint Louis University
Junfeng Zhang: China University of Geosciences
Jianguo Wen: Argonne National Laboratory
Julien Gasc: École Normale Supérieure PSL Research University
Sarah Incel: École Normale Supérieure PSL Research University
Alexandre Schubnel: École Normale Supérieure PSL Research University
Ziyu Li: Saint Louis University
Tao Chen: China University of Geosciences
Wenlong Liu: China University of Geosciences
Vitali Prakapenka: The University of Chicago
Zhenmin Jin: China University of Geosciences

Nature Communications, 2018, vol. 9, issue 1, 1-13

Abstract: Abstract Southern Tibet is the most active orogenic region on Earth where the Indian Plate thrusts under Eurasia, pushing the seismic discontinuity between the crust and the mantle to an unusual depth of ~80 km. Numerous earthquakes occur in the lower portion of this thickened continental crust, but the triggering mechanisms remain enigmatic. Here we show that dry granulite rocks, the dominant constituent of the subducted Indian crust, become brittle when deformed under conditions corresponding to the eclogite stability field. Microfractures propagate dynamically, producing acoustic emission, a laboratory analog of earthquakes, leading to macroscopic faults. Failed specimens are characterized by weak reaction bands consisting of nanometric products of the metamorphic reaction. Assisted by brittle intra-granular ruptures, the reaction bands develop into shear bands which self-organize to form macroscopic Riedel-like fault zones. These results provide a viable mechanism for deep seismicity with additional constraints on orogenic processes in Tibet.

Date: 2018
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DOI: 10.1038/s41467-018-05964-1

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