The velocity structure of a fossil spreading centre in the Southwest Sub-basin, South China Sea

We present results from an ocean bottom seismometer experiment surveying the fossil spreading centre in the Southwest Sub‐basin of the South China Sea. The detailed velocity model shows that oceanic layer 2 exhibits across‐axis variations in thickness and velocity, whereas oceanic layer 3 displays a...

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Bibliographic Details
Published in:Geological journal (Chichester, England) England), 2016-08, Vol.51 (S1), p.548-561
Main Authors: Zhang, Jie, Li, Jiabiao, Ruan, Aiguo, Wu, Zhenli, Yu, Zhiteng, Niu, Xiongwei, Ding, Weiwei
Format: Article
Language:English
Subjects:
crustal structure
fossil spreading centre
Marine
South China Sea
Southwest Sub-basin
wide-angle seismic refraction
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Summary:We present results from an ocean bottom seismometer experiment surveying the fossil spreading centre in the Southwest Sub‐basin of the South China Sea. The detailed velocity model shows that oceanic layer 2 exhibits across‐axis variations in thickness and velocity, whereas oceanic layer 3 displays a variation in crustal thickness. A low‐angle (24°) SE‐dipping oceanic detachment fault is proposed to explain the anomalous structure on the NW side of the spreading centre, which exhibits uplifting of the upper mantle beneath a thinned oceanic crust. The inferred oceanic detachment fault was at its initial stage, localized within the basaltic crust and did not exhume lower crust. We suggest that the low‐velocity (7.6–7.9 km/s) body located within the upper mantle beneath the footwall of the detachment fault is caused by both mantle serpentinization and partial melting. The difference in crustal thickness in the Southwest Sub‐basin indicates that the magma supply varied in time and space during or even after the seafloor spreading. Compared with other fossil spreading ridges, the fossil spreading centre of the northeast Southwest Sub‐basin studied here represents a third type of fossil spreading ridge, characterized by a reduced melt supply at the waning stage of spreading and a strong post‐spreading magmatism. Copyright © 2016 John Wiley & Sons, Ltd.
ISSN:0072-1050
1099-1034
DOI:10.1002/gj.2778