HR: 1330h
AN: T12A-0444    [PDF]
TI: The crustal structures of the continent-ocean transition zone in the northern South China Sea
AU: * Tsai, C
EM: chtsai@oc.gep.ncu.edu.tw
AF: Institute of Geophysics, National Central University, 300, Chungda Road, Chungli, Chungli, 32054
AU: Hsu, S
EM: hsu@oc.gep.ncu.edu.tw
AF: Institute of Geophysics, National Central University, 300, Chungda Road, Chungli, Chungli, 32054
AU: Yeh, Y
EM: greenleaf@oc.gep.ncu.edu.tw
AF: Institute of Geophysics, National Central University, 300, Chungda Road, Chungli, Chungli, 32054
AU: Lee, C
EM: leecs@mail.ntou.edu.tw
AF: Institute of Applied Geophysics National Taiwan Ocean University, 2, Pei-Ning Road, Keelung, 20224
AB: The continent-ocean Boundary (COB) in the northern South China Sea (SCS) was suggested to be almost along a 3000m-isobath near the northern continental slope. According to the magnetic anomaly identification, the age of the South China Sea oceanic crust is about 30 to 15 Ma and the northernmost oceanic crust is distributed near 18›X30­ÝN. To the north, due to lack of good correlated magnetic data and deep seismic profiles, most studies do not suggest the existence of the oceanic crust. However, new magnetic evidence indicates that the oceanic crust may extend to 21›X30­ÝN. In this study, we carried out a synthesis of the existing seismic reflection profiles across the COB zone. We also used the corresponding gravity anomalies and a simple four-layer crustal model to simulate the depth variation of the Moho discontinuity across the SCS northern margin. Based on our results, we can distinguish the SCS northern margin into three portions: the western, the middle and the eastern portions. In the western portion, our crustal models show a good agreement with the previous studies. The COB follows the 3000m-isobath and a continent-ocean transition zone (COT) spreads ca.150-250 km wide. In the eastern portion, our models bring out completely new insights. We find that the COB is close to the continental shelf and is along ca 2000m-isobath. The crustal pattern from continental to oceanic has changed quickly. The COT is much narrower than the western portion. The middle portion, including the Dongsha Rise, seems to be a high platform and comprises many intruded or extruded igneous bodies, revealed by bathymetry and seismic data. This phenomenon is quite different from the other two potions of the study area. Our results show the crustal thickness below this region is still thin (ca. 8-9 km close to normal oceanic crust thickness) but is thicker than surrounding area. We suggest that the igneous events have affected the original oceanic crust, which provides a possible mechanism for the formation of the Dongsha Rise. The range of COT is about 200 km in this portion.
DE: 3010 Gravity
DE: 3025 Marine seismics (0935)
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
DE: 3210 Modeling
SC: Tectonophysics [T]
MN: 2003 Fall Meeting