Although long-lived detachment faulting plays an important role in fluid circulation and in accommodating tectonic extension at slow-spreading oceanic ridges, it is still unclear how the fluid-enriched faults contribute to the observed seismic anisotropy in the lower crust. We investigated sheared and altered gabbros along the detachment fault zones from the Xigaze ophiolite in the southern Tibetan Plateau. Results demonstrate that the positive feedback between fluid circulation and shearing, linked by dissolution-precipitation creep of amphibole, resulted in fluid enrichment during strain localization along the fault zones. Based on this shearing-enhanced fluid circulation model, our calculations of the seismic properties show that amphiboles (de)formed by dissolution-precipitation creep along the fault zones largely contribute to the seismic anisotropy (P and S waves) and S-wave delay time in the lower crust at slow-spreading ridges, with the polarization directions of fast shear waves being subparallel to the ridges. The strength of resulting seismic anisotropy is largely a function of crustal thickness, fault zone attitude, and metasomatism intensity. This study provides a novel explanation for the origin of seismic anisotropy in the lower oceanic crust at slow-spreading ridges. The conclusion may also have implications for the origin of seismic anisotropy at fast-spreading ridges where there are high melt supplies.
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Research Article|
March 15, 2023
Shearing-enhanced deep fluid circulation induces seismic anisotropy in the lower crust at slow-spreading oceanic ridges
Baojun Zhou;
Baojun Zhou
1
State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, China
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Junlai Liu;
Junlai Liu
1
State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, China
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Jiaxin Yan;
Jiaxin Yan
1
State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, China
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Chunru Hou;
Chunru Hou
1
State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, China
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Xiaoyu Chen;
Xiaoyu Chen
1
State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, China
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Chuanzhou Liu;
Chuanzhou Liu
2
State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
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Fuyuan Wu
Fuyuan Wu
2
State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
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Baojun Zhou
1
State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, China
Junlai Liu
1
State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, China
Jiaxin Yan
1
State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, China
Chunru Hou
1
State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, China
Xiaoyu Chen
1
State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, China
Chuanzhou Liu
2
State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
Fuyuan Wu
2
State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
Publisher: Geological Society of America
Received:
26 Oct 2022
Revision Received:
31 Dec 2022
Accepted:
09 Jan 2023
First Online:
15 Mar 2023
Online Issn: 1943-2682
Print Issn: 0091-7613
© 2023 Geological Society of America
Geology (2023)
Article history
Received:
26 Oct 2022
Revision Received:
31 Dec 2022
Accepted:
09 Jan 2023
First Online:
15 Mar 2023
Citation
Baojun Zhou, Junlai Liu, Jiaxin Yan, Chunru Hou, Xiaoyu Chen, Chuanzhou Liu, Fuyuan Wu; Shearing-enhanced deep fluid circulation induces seismic anisotropy in the lower crust at slow-spreading oceanic ridges. Geology 2023; doi: https://doi.org/10.1130/G50879.1
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