Crustal structure and inferred rifting processes in the northeast South China Sea |
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| Institution: | 1. Key Laboratory of Marine Geology and Environment, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China;2. Sanya Institute of Deep-Sea Science and Engineering, Chinese Academy of Sciences, Sanya 572000, China;3. Institute for Geophysics, University of Texas at Austin (R2200), 10100 Burnet Road, Austin, TX 78758-0000, USA;4. Exploration Department, China National Offshore Oil Corporation Ltd., Beijing 100010, China;5. Guangzhou Marine Geological Survey Bureau, Ministry of Land and Resources, Guangzhou 510075, China;6. University of Chinese Academy of Sciences, Beijing 100049, China;1. The Second Institute of Oceanography, State Oceanic Administration, Hangzhou 310012, China;2. Department of Earth Sciences, Zhejiang University, Hangzhou 310027, China;1. Ifremer Centre de Brest, BP 70, 29280 Plouzané Cedex, France;2. 44 rue du Cloître, Plouzané, France;3. Taiwan Ocean Research Institute, 219, Sec. 1 Dongfang Rd., Qieding Dist., Kaohsiung 852, Taiwan;4. Institute of Applied Geophysics, National Taiwan Ocean University, 2 Pei-Ning Road, Keelung 202, Taiwan |
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| Abstract: | TAIGER project deep-penetration seismic reflection profiles acquired in the northeastern South China Sea (SCS) provide a detailed view of the crustal structure of a very wide rifted continental margin. These profiles document a failed rift zone proximal to the shelf, a zone of thicker crust 150 km from the shelf, and gradually thinning crust toward the COB, spanning a total distance of 250–300 km. Such an expanse of extended continental crust is not unique but it is uncommon for continental margins. We use the high-quality images from this data set to identify the styles of upper and lower crustal structure and how they have thinned in response to extension and, in turn, what rheological variations are predicted that allow for protracted crustal extension. Upper crustal thinning is greatest at the failed rift (βuc ≈ 7.5) but is limited farther seaward (βuc ≈ 1–2). We interpret that the lower crust has discordantly thinned from an original 15–17 km to possibly less than 2–3 km thick beneath the central thick crust zone and more distal areas. This extreme lower crustal thinning indicates that it acted as a weak layer allowing decoupling between the upper crust and the mantle lithosphere. The observed upper crustal thickness variations and implied rheology (lower crustal flow) are consistent with large-scale boudinage of continental crust during protracted extension. |
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| Keywords: | Rifted margin Extension Normal fault Crustal structure South China Sea Seismic |
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