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Seismic Constraint From V p / V s Ratios on the Structure and Composition Across the Continent‐Ocean Transition Zone, South China Sea
Author(s) -
Li Yuhan,
Grevemeyer Ingo,
Huang Haibo,
Qiu Xuelin,
Xu Ziying
Publication year - 2021
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2021gl094656
Subject(s) - geology , crust , oceanic crust , continental crust , mantle (geology) , transition zone , lithology , magmatism , rift , flood basalt , continental margin , volcano , basement , seismology , petrology , geochemistry , subduction , volcanism , tectonics , civil engineering , engineering
At non‐volcanic passive continental margins, seismic techniques often failed to uniquely define the nature of crustal domains. Here, we overcome this problem by studying the structure and composition of the continent‐ocean transition (COT) in the Southwest Sub‐basin of the South China Sea, using P and S wave seismic tomography and V p / V s ratios, providing unique constraints on lithology. Throughout the image domain, we can rule out large areas of exhumed mantle as V p / V s ratios are always <1.9 in the shallow basement layer. Instead, the COT is characterized by extended and fragmented continental crust, and possibly mafic aggregation at the bottom of the crust. In concert with observations from multichannel seismic reflection data, seismic velocities and V p / V s ratios suggest that the oldest oceanic crust was formed by starved magmatism, causing rugged basement, thin crust, nearly absent lower crust, and moderately serpentinized mantle below. Our results reveal that rifting occurred without un‐roofing continental mantle.