Journal
MARINE GEOLOGY
Volume 410, Issue -, Pages 70-87Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.margeo.2018.12.007
Keywords
Crustal structure; Continental margin morphology; Magmatic intrusion; Wide-angle seismic data; South China Sea
Categories
Funding
- National Natural Science Foundation of China (NSFC) [41576041, U1701641, 41576070, 91328206]
- National Natural Science Foundation of Guangdong Province [2017A030311015, 2017A030310340]
- Rising Star Foundation of the South China Sea Institute of Oceanology [NHXX2017DZ0101]
- NSFC Open Research Cruise [NORC2014-08]
- Shiptime Sharing Project of NSFC
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The northeastern margin of the South China Sea experienced continental rifting followed by magmatism in the Cenozoic. This evolution has strongly influenced the heterogeneity of its crustal structure. To gain insights into the spatial variation in crustal structure, data from 30 ocean bottom seismometers were used to forward model ten P-wave velocity models along both dip and strike directions. The Cenozoic strata (1.7-3.5 km/s), the Mesozoic strata (3.5-5.5 km/s), the crystalline crust (5.5-7.5 km/s) and high velocity lower crust (7.0-7.5 km/s) were identified based on P-wave velocities. Overall, the crust thins from similar to 25 km on the continental shelf to similar to 15 km on the slope, with thicker crust underneath the Dongsha Basin (a Mesozoic basin) but thinner crust underneath the pre-Cenozoic NW-trending fault zones. This difference in thickness is possibly controlled by different strength of inherited structures, i.e., the Dongsha Basin and the fault zones. Furthermore, a widespread high velocity lower crust layer, which resulted from the intrusion of a mafic sill complex, was observed over the shelf to slope. Mafic intrusions within the lower crust have uplifted the caprock on the shelf, and magma eruptions have formed many post-rift seamounts on the slope. The evidence suggests that post-rift magmatism overprinted the vertical crustal structure. We therefore propose that the heterogeneous crustal structures in this passive margin are an integrated result of segmental extension followed by magmatic overprinting.
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