Shearing-enhanced deep fluid circulation induces seismic anisotropy in the lower crust at slow-spreading oceanic ridges

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 a...

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Bibliographic Details
Published in:Geology (Boulder) 2023-05, Vol.51 (5), p.465-470
Main Authors: Zhou Baojun, Zhou Baojun, Liu Junlai, Liu Junlai, Yan Jiaxin, Yan Jiaxin, Hou Chunru, Hou Chunru, Chen Xiaoyu, Chen Xiaoyu, Liu Chuanzhou, Liu Chuanzhou, Wu Fuyuan, Wu Fuyuan
Format: Article
Language:English
Subjects:
Amphiboles
Anisotropy
Asia
body waves
Circulation
crust
Crustal thickness
Delay time
detachment faults
Dissolution
Dissolving
elastic waves
extension tectonics
Fault zones
faults
Gabbros
Geological faults
Geology
geophysical methods
Localization
lower crust
melts
metasomatism
microstructure
Oceanic crust
Oceanic ridges
P-waves
Positive feedback
Precipitation
Ridges
S waves
Seismic activity
seismic methods
Seismic properties
seismic waves
shear zones
Shearing
Solifluction
Spreading
Spreading centres
Strain localization
Structural geology
Submarine ridges
Tectonics
Tibetan Plateau
Xigaze Ophiolite
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Summary: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.
ISSN:0091-7613
1943-2682
DOI:10.1130/G50879.1