Crustal structures of the northernmost South China Sea
Chien-Wei Huang
Abstract
The age of the South China Sea (SCS) oceanic crust was previously believed between ca. 32 and 15 Ma. Hsu et al. (2004) acquired a new magnetic data in the northernmost SCS, beyond the oldest oceanic crust previously identified, and it shows clearly the existence of E-W trending magnetic polarity reversal patterns.
Hsu et al. (2004) suggest that the northern extension of the SCS oceanic crust is terminated by an inactive NW¡VSE trending trench-trench transform fault, called the Luzon¡VRyukyu Transform Plate Boundary (LRTPB).There are the different patterns of the magnetic anomalies and basement depth on both sides of the LRTPB. The northwestern portion of the LRTPB is along the Formosa Canyon (FC). It shows a northeast-dipping escarpment, not classic canyon. The new identified continent¡Vocean boundary (COB) in the northern SCS is generally relatively low magnetization zone, corresponding to the thinned portion of the continental crust.
To realize the crustal structure, Yeh and Hsu (2004) analyzed seismic profiles of the region. They also performed gravity modeling to understand the Moho depth variation. The crust in the region is generally thinner from NW to SE. The northernmost SCS can be divided into three regions according to the locations of the LRTPB and the seismic results. The crust beneath the LRTPB is relatively thin from gravity modeling. However, probably because of post-spreading volcanism, the transtension-shearing phenomenon of volcanic basement in the LRTPB is not observed generally. The erosion occurs along the whole channel of the FC.
References
Hsu, S.-K., Yeh, Y.-C., Doo, W.-B. and Tsai, C.-H., 2004, New bathymetry and magnetic lineations identifications in the northernmost South China Sea and their tectonicimplications, Marine Geophysical Researches 25, 29-44.
Yeh Y.-C. and Hsu S.-K., 2004, Crustal structures of the northernmost South China Sea: Seismic reflection and gravity modeling, Marine ?Geophysical Researches 25, 45-61.