Velocity structure revealing a likely mud volcano off the Dongsha Island, the northern South China Sea
Velocity structure revealing a likely mud volcano off the Dongsha Island, the northern South China Sea
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速度结构揭示南海北部东沙岛附近可能存在泥火山
DOI：
10.3390/en15010195
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发表时间：
2021
期刊：
影响因子：
3.2
通讯作者：
Lixin Wang
中科院分区：
文献类型：
--
作者：
Yuning Yan;Jianping Liao;Junhui Yu;Changliang Chen;Guangjian Zhong;Yanlin Wang;Lixin Wang
东沙岛位于南海中北部大陆边缘。其周围的沃茨位于潮汕坳陷之下，潮汕坳陷是一个残留的中生代沉积盆地，被薄的新生代沉积物覆盖，但居住着许多海底丘陵，但鲜为人知的性质。东沙岛东南面有一座高300 m、宽10 km的H110大山，海底地震和多道地震测线穿过该大山。利用海底地震数据进行的初至层析成像显示了其下方的两个明显现象：（1）低速区（3.3至4公里/秒），面积为20 × 3平方公里，中心位于~4.5公里深度;（2）下方高速区（5.5至6.3公里/秒），面积相当，深度约为7公里。MCS剖面显示出非常破碎的新生代层序，在H110山下方的中生代地层中覆盖了一个广泛的混乱反射带。低速带对应于混乱的反射带，可以解释为高度破裂和富含流体的中生界层。从H110挖掘的样品包括含伊利石的自生碳酸盐结核和丰富的深水生物，表明烃类从深源渗漏。因此，H110可以推断为泥火山。高速带被解释为岩浆侵入，考虑到年轻的岩浆活动被发现在南部CSD增强。此外，H110的起源可以推测为受磁场驱动，即，深部岩浆侵入厚层中生代地层，促进油气生成，从而驱动泥火山作用。H110的泥火山活动及其下方低速带的出现，可能预示着中生界油气藏的存在，这对油气勘探是有利的。
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 km2, 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.