Velocity Structure Revealing a Likely Mud Volcano off the Dongsha Island, the Northern South China Sea

Yuning Yan, Jianping Liao, Junhui Yu, Changliang Chen, Guangjian Zhong, Yanlin Wang and Lixin Wang
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Yuning Yan: Hunan Provincial Key Laboratory of Shale Gas Resource Utilization, Hunan University of Science and Technology, Xiangtan 411201, China
Jianping Liao: Hunan Provincial Key Laboratory of Shale Gas Resource Utilization, Hunan University of Science and Technology, Xiangtan 411201, China
Junhui Yu: Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou), Guangzhou 511458, China
Changliang Chen: Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou), Guangzhou 511458, China
Guangjian Zhong: Guangzhou Marine Geological Survey, Guangzhou 510760, China
Yanlin Wang: Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou), Guangzhou 511458, China
Lixin Wang: SINOPEC Key Laboratory of Geophysics, Sinopec Geophysical Research Institute, Nanjing 211103, China

Energies, 2021, vol. 15, issue 1, 1-17

Abstract: The Dongsha Island (DS) is located in the mid-northern South China Sea continental margin. The waters around it are underlain by the Chaoshan Depression, a relict Mesozoic sedimentary basin, blanketed by thin Cenozoic sediments but populated with numerous submarine hills with yet less-known nature. A large hill, H110, 300 m high, 10 km wide, appearing in the southeast to the Dongsha Island, is crossed by an ocean bottom seismic and multiple channel seismic surveying lines. The first arrival tomography, using ocean bottom seismic data, showed two obvious phenomena below it: (1) a low-velocity (3.3 to 4 km/s) zone, with size of 20 × 3 km 2 , centering at ~4.5 km depth and (2) an underlying high-velocity (5.5 to 6.3 km/s) zone of comparable size at ~7 km depth. MCS profiles show much-fragmented Cenozoic sequences, covering a wide chaotic reflection zone within the Mesozoic strata below hill H110. The low-velocity zone corresponds to the chaotic reflection zone and can be interpreted as of highly-fractured and fluid-rich Mesozoic layers. Samples dredged from H110 comprised of illite-bearing authigenic carbonate nodules and rich, deep-water organisms are indicative of hydrocarbon seepage from deep source. Therefore, H110 can be inferred as a mud volcano. The high-velocity zone is interpreted as of magma intrusion, considering that young magmatism was found enhanced over the southern CSD. Furthermore, the origin of H110 can be speculated as thermodynamically driven, i.e., magma from the depths intrudes into the thick Mesozoic strata and promotes petroleum generation, thus, driving mud volcanism. Mud volcanism at H110 and the occurrence of a low-velocity zone below it likely indicates the existence of Mesozoic hydrocarbon reservoir, which is in favor of the petroleum exploration.

Keywords: Dongsha Waters in the northern South China Sea margin; velocity inversion; mud volcano; magma intrusion; Mesozoic hydrocarbon (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2021
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