Crustal structure and extension mode in the northwestern margin of the South China Sea

• Published in: Geochemistry, geophysics, geosystems : G3 Vol. 17; no. 6; pp. 2143 - 2167
• Main Authors: Gao, Jinwei, Wu, Shiguo, McIntosh, Kirk, Mi, Lijun, Liu, Zheng, Spence, George
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 01.06.2016
• Subjects: Continental crust; Continental margins; crustal structure; gravity modeling; Lithosphere; Magma; multichannel seismic data; Ocean floor; Oceanography; Plate tectonics; Rifting; rifting process; Seafloor spreading; Seamounts; Seismology; South China Sea; Thinning; Transition zone; Unconformity; Xisha Trough; ISEW, South China Sea; ISEW, South China Sea, Xisha Trough
• ISSN: 1525-2027; 1525-2027
• DOI: 10.1002/2016GC006247

Combining multi‐channel seismic reflection and gravity modeling, this study has investigated the crustal structure of the northwestern South China Sea margin. These data constrain a hyper‐extended crustal area bounded by basin‐bounding faults corresponding to an aborted rift below the Xisha Trough with a subparallel fossil ridge in the adjacent Northwest Sub‐basin. The thinnest crust is located in the Xisha Trough, where it is remnant lower crust with a thickness of less than 3 km. Gravity modeling also revealed a hyper‐extended crust across the Xisha Trough. The postrift magmatism is well developed and more active in the Xisha Trough and farther southeast than on the northwestern continental margin of the South China Sea; and the magmatic intrusion/extrusion was relatively active during the rifting of Xisha Trough and the Northwest Sub‐basin. A narrow continent‐ocean transition zone with a width of ∼65 km bounded seaward by a volcanic buried seamount is characterized by crustal thinning, rift depression, low gravity anomaly and the termination of the break‐up unconformity seismic reflection. The aborted rift near the continental margin means that there may be no obvious detachment fault like that in the Iberia‐Newfoundland type margin. The symmetric rift, extreme hyper‐extended continental crust and hotter mantle materials indicate that continental crust underwent stretching phase (pure‐shear deformation), thinning phase and breakup followed by onset of seafloor spreading and the mantle‐lithosphere may break up before crustal‐necking in the northwestern South China Sea margin. Key Points Multichannel seismic reflection and satellite gravity data in the northwestern South China Sea Seismic images and gravity modeling indicate a hyper‐extended continental margin Mantle‐lithosphere may break up before crustal‐necking in the northwestern South China Sea margin