HR: 1340h
AN: GP23A-0023    [Abstracts]
TI: Oldest age of South China Sea seafloor spreading identified by marine magnetic anomaly
AU: * Hsu, S
EM: hsu@oc.gep.ncu.edu.tw
AF: Institute of Geophysics, National Central University, Taiwan, Institute of Geophysics, National Central University, Chung-Li, 32001 Taiwan
AU: Yeh, Y
EM: greenleaf@oc.gep.ncu.edu.tw
AF: Institute of Geophysics, National Central University, Taiwan, Institute of Geophysics, National Central University, Chung-Li, 32001 Taiwan
AU: Doo, W
EM: flexure@oc.gep.ncu.edu.tw
AF: Institute of Geophysics, National Central University, Taiwan, Institute of Geophysics, National Central University, Chung-Li, 32001 Taiwan
AB: The oldest age of the South China Sea (SCS) seafloor spreading was previously believed to be ca. 32 (magnetic anomaly C11). New magnetic data acquired in the northernmost SCS however obviously shows the existence of oceanic-crust-related E-W trending magnetic polarity reversal patterns. Through magnetic modeling, the oldest SCS oceanic crust was dated at Late Eocene, as old as 37 Ma (magnetic anomaly C17), with a half-spreading rate of 40 mm/yr. The corresponding continent-ocean boundary (COB) in the northern SCS is therefore put a little bit northward. The SCS oceanic crust is limited in the west by the presence of a relatively low magnetization zone, corresponding to outermost thinned portion of the continental crust. The northward extension of the oldest SCS oceanic crust is found to be terminated by a NW-SE trending transform fault, called the Luzon-Ryukyu Transform Plate Boundary (LRTPB). The LRTPB is supposed to be a former left-lateral transform fault connecting the former southeast-dipping Manila Trench in the south and the northwest-dipping Ryukyu Trench in the north. The oldest age of the SCS oceanic crust identified in the northernmost SCS by marine magnetic anomalies indicates that the initiation of the SCS seafloor spreading occurred in the northeastern and southeastern corners. However, an older SCS oceanic crust than 37 Ma cannot be excluded. The spreading age younger towards southwest indicates that there was a SCS mid-ocean ridge propagation southwestward or a different stages of the SCS seafloor spreading; the SCS seafloor spreading occurred first in the east and then in the west.
DE: 1500 GEOMAGNETISM AND PALEOMAGNETISM
DE: 1517 Magnetic anomalies: modeling and interpretation
DE: 3000 MARINE GEOLOGY AND GEOPHYSICS
DE: 3005 Marine magnetics and paleomagnetics (1550)
DE: 8100 TECTONOPHYSICS
SC: Geomagnetism and Paleomagnetism [GP]
MN: Fall Meeting 2005