Preliminary Paleomagnetic Results of Cores Collected during IODP Expedition 349 South China Sea Tectonics

Wednesday, 17 December 2014: 8:45 AM
Xixi Zhao, University of California Santa Cruz, Santa Cruz, CA, United States; State Key Laboratory of Marine Geology, Tongji University, Shanghai, 200092, Shanghai, China and Qingsong Liu, IGG Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China
International Ocean Discovery Program (IODP) Expedition 349 investigated the tectonic and oceanographic evolution of the South China Sea (SCS). The SCS is a marginal sea of the western Pacific and has undergone a near complete Wilson cycle from continental breakup to seafloor spreading to subduction along the Manila Trench. Two of the primary objectives of Expedition 349 are to determine the initiation and termination age of seafloor spreading through direct sampling of oceanic crust and to elucidate the cause of differences in seafloor magnetic anomalies between the East and Southwest Subbains. Expedition 349 drilled five sites in the deep basin of the SCS. Sites U1431, U1433, and U1434 recovered oceanic basement and overlying sediments near fossil spreading centers, and Sites U1432 and U1435 recovered materials near or at the northern continent/ocean boundary. Preliminary paleomagnetic results show that sediments and basement rocks from the sites drilled by Expedition 349 contain both reversely and normally magnetized samples. Our paleomagnetic study involves detailed alternating field and thermal demagnetization analysis of discrete samples. Stable characteristic remanent magnetization (ChRM) components are observed throughout the studied cores, following removal of a low stability drilling-induced remanence. Inclination values of ChRM are moderate downward or upward, consistent with the expected inclination for the sites. In order to examine the origin of the ChRM, supportive rock magnetic experiments on the same samples used for magnetostratigraphy of the drill sites were also conducted. Preliminary shipboard interpretations of biostratigraphic data from these sites indicate that the fossils needed to anchor the magnetostratigraphy are available. Preliminary magnetostratigraphy for Expedition 349 sites should help to refine the ages of sedimentation events and tectonic activities within and beyond the South China Sea basin.