[M-IS32] Drilling Earth Science

[MIS32-06] Probing the Tectonic Evolution of the South China Sea: International Ocean Discovery Program Expedition 349

*Maria luisa TEJADA¹, Chun-feng LI², Jian LIN³, Denise KULHANEK⁴, Trevor WILLIAMS⁵, Rui BAO⁶, Anne BRIAIS⁷, Yifeng CHEN⁸, Peter CLIFT⁹, Frederick COLWELL¹⁰, Kelsie DADD¹¹, Weiwei DING¹², Ivan HERNANDEZ-ALMEIDA¹³, Xiao-long HUANG⁸, Sangmin HYUN¹⁴, Tao JIANG¹⁵, Anthony KOPPERS¹⁰, Qianyu LI², Chuanlian LIU², Qingsong LIU¹⁶, Zhifei LIU², Renata NAGAI¹⁷, Alyssa PELEO-ALAMPAY¹⁸, Xin SU¹⁹, Zhen SUN²⁰, Hai son TRINH²¹, Yi-ching YEH²², Chuanlun ZHANG², Fan ZHANG³, Guo-liang ZHANG²³, Xixi ZHAO² (1.Department of Solid Earth Geochemistry, Japan Agency for Marine-Earth Science and Technology, Japan, 2.State Key Laboratory of Marine Geology, Tongji University, China, 3.Woods Hole Oceanographic Institution, USA, 4.IODP, Texas A&M University, USA, 5.Lamont-Doherty Earth Observatory of Columbia University, USA, 6.Geologisches Institut, Swiss Federal Institute of Technology, Switzerland, 7.Centre National de la Reserche Scientifique, University of Toulouse, France, 8.Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, China, 9.Department of Geology and Geophysics, Louisiana State University, USA, 10.College of Earth, Ocean and Atmospheric Sciences, Oregon State University, USA, 11.Department of Earth and Planetary Sciences, Macquarie University, Australia, 12.Second Institute of Oceanography, State Oceanic Administration, China, 13.Institute of Geography/Oeschger Centre for Climate Change Research, Univ. of Bern, Switzerlandl, 14.Korea Institute of Ocean Science and Technology, Republic of Korea, 15.Faculty of Earth Resources, China University of Geosciences, China, 16.State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, CAS, China, 17.Department of Physical, Chemical and Geological Oceanography, Universidade de Sao Paulo, Brazil, 18.National Institute of Geological Sciences, Univ. of the Philippines, Philippines, 19.School of Marine Geosciences, China University of Geosciences, China, 20.South China Sea Institute of Oceanology, Chinese Academy of Sciences, China, 21.Department of Science and Technology, Min. of Natural Resources and Environment, Vietnam, 22.Taiwan Ocean Research Institute, Taiwan, Republic of China, 23.Key Laboratory of Marine Geology and Environment, Institute of Oceanology, CAS, China)

Keywords:South China Sea, tectonic evolution, seafloor spreading, International Ocean Discovery Program, Expedition 349, oceanic crust drilling

Expedition 349, South China Sea (SCS) Tectonics, was the first voyage of the JOIDES Resolution under the new International Ocean Discovery Program. The objectives of this expedition were to: 1) determine the timing, mechanisms, and sequence of the opening and closing of different subbasins of the SCS by coring and directly dating the oceanic crust; 2) investigate the tectonic history of the SCS by conducting biostratigraphic and magnetostratigraphic investigations on the sedimentary sequences to help constrain the timing and sequence of geologic events and the sedimentary responses to tectonic evolution of the basin; 3) measure the geochemical composition, magnetization, and physical properties of the oceanic crust and seamount volcanic products to understand crustal accretion and deep mantle processes associated with the tectonic development of the basin; and 4) test the different proposed driving mechanisms that led to continental breakup and seafloor spreading. To attain these objectives, we cored near the ocean-continent boundary (U1432 and U1435) inferred to be underlain by the oldest oceanic crust, and near the fossil spreading centers in the East Subbasin (U1431) and the Southwest Subbasin (U1433 and U1434) where the youngest crust formed. The main scientific outcomes of Expedition 349 include 1) in-situ SCS oceanic crust was recovered for the first time, providing critical control on the timing of termination of spreading in the SCS; 2) the cessation age of spreading in both the East and Southwest Subbasins are similar (~16 Ma), based on shipboard biostratigraphy from reddish-brown clays overlying and within the oceanic crust at Sites U1431 and U1433; and 3) determination of the nature of the structural high at Site U1435, where a sharp, possibly rift-related unconformity was recovered, providing indirect evidence for the onset of seafloor spreading at ~33 Ma. In addition, 4) the nature of post-spreading seamount volcanism will be examined from the volcaniclastic sediments recovered at Sites U1431 and U1434; and 5) the past environmental, climatic, and oceanographic conditions related to the tectonic evolution of the SCS will be gleaned from studies of the 1524 m of sedimentary deposits recovered from all sites.