| 麻坑、泥火山在南海北部与西部陆缘的分布特征和地质意义 |
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| 引用本文： | 陈江欣,关永贤,宋海斌,杨胜雄,耿明会,拜阳,刘伯然.麻坑、泥火山在南海北部与西部陆缘的分布特征和地质意义[J].地球物理学报,2015,58(3):919-938. |
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| 作者姓名： | 陈江欣 关永贤 宋海斌 杨胜雄 耿明会 拜阳 刘伯然 |
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| 作者单位： | 1. 中国科学院油气资源研究重点实验室, 中国科学院地质与地球物理研究所, 北京 100029;
2. 中国科学院大学, 北京 100049;
3. 国土资源部海底矿产资源重点实验室, 广州海洋地质调查局, 广州 510760;
4. 海洋地质国家重点实验室, 同济大学海洋与地球科学学院, 上海 200092 |
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| 基金项目： | 国家自然科学基金重大计划重点项目(91128205)和国家重点基础研究发展计划(973)(2011CB403503)资助. |
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| 摘 要： | 本文利用新的高分辨率海底多波束地形数据与以往研究资料对南海台西南盆地及以西和中建南盆地北部及以北陆缘区域内的麻坑与泥火山分布区进行了统计、分析与总结.本文提出根据麻坑的个体平面形态、规模量级和组合形式建立麻坑的三类分类体系并进行总结阐述.麻坑的直径与坑深总体具有线性变化关系但又有区域性分布特征,可能反映了不同海区底质性质、浅地层构造活动、海底倾斜程度和海底底流等因素的不同影响;同一区域泥火山的直径与高度具有线性关系而不同区域拟合斜率差异较大,可能说明同区域泥火山形态、流体成分和来源具有高度一致性,但其分布具有区域差异性特征.研究表明,麻坑、泥火山的产生与近5Ma新构造运动期内台湾南部和南海西缘区域性走滑断裂活动相一致,主要分布在构造活动较为活跃,沉积较为薄弱的近坡折带和大陆坡区域,在具有走滑性质的台西南、莺歌海和中建南盆地分布较广、规模较大,而在其他主要张裂性质盆地中分布较少,规模较小.其分布特征一方面能够说明某些区域流体的大量渗漏与逸散,另一方面也能够说明某些区域持续的构造活动有利于该区域深部流体的重新聚集与成藏,从而成为指导油气资源勘探的重要参考指标.
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| 关 键 词： | 麻坑 泥火山 新构造运动 流体 南海 |
| 收稿时间： | 2014-05-13 |
Distribution characteristics and geological implications of pockmarks and mud volcanoes in the northern and western continental margins of the South China Sea |
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| CHEN Jiang-Xin,GUAN Yong-Xian,SONG Hai-Bin,YANG Sheng-Xiong,GENG Ming-Hui,BAI Yang,LIU Bo-Ran.Distribution characteristics and geological implications of pockmarks and mud volcanoes in the northern and western continental margins of the South China Sea[J].Chinese Journal of Geophysics,2015,58(3):919-938. |
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| Authors: | CHEN Jiang-Xin GUAN Yong-Xian SONG Hai-Bin YANG Sheng-Xiong GENG Ming-Hui BAI Yang LIU Bo-Ran |
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| Institution: | 1. Key Laboratory of Petroleum Resources Research, Institute of Geology and Geophysics, Beijing 100029, China;
2. University of Chinese Academy of Sciences, Beijing 100049, China;
3. Key Laboratory of Marine Mineral Resources, Ministry of Land and Resources, Guangzhou Marine Geological Survey, Guangzhou 510760, China;
4. State Key laboratory of Marine Geology, School of Ocean and Earth Science, Tongji University, Shanghai 200092, China |
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| Abstract: | New high resolution multi-beam bathymetry data and previous research data are used to study the distribution characteristics of pockmarks and mud volcanoes, such as location, size and morphology, in the northern continental margin consisting of Southwest Taiwan Basin and to the west and the western continental margin consisting of Zhongjiannan Basin and to the north. Combined with the tectonic evolution and topography of the northern and western margin of the South China Sea (SCS), this work made statistics, and classification to these characters, and linked them with the geological evolution of the South China Sea and the distribution of oil and gas resources.
The SCS is surrounded by different types of continental margins. To the north is the extensional continental margin which consists of Southwest Taiwan Basin(Ⅰ), Pearl River Mouth Basin(Ⅱ) and Qiongdongnan Basin(Ⅲ); to the west is the strike-slip continental margin which consists of Beibuwan Basin(Ⅳ), Yinggehai Basin(Ⅴ) and Zhongjiannan Basin(Ⅵ); to the east is the subducted continental margin and to the south is the margin of continental collision. All the basins above have experienced almost the same stages during evolution of the SCS, which include Paleocene to mid-Miocene rifting followed by post-rift thermal subsidence and the neotectonic movement in recent ~5 Ma. In the study area, 16 distribution areas (a—p) of pockmarks and mud volcanoes are recognized. The data of areas a, b, c, d, and h were collected from previous researches and the other data were collected by the Guangzhou Marine Geological Survey in 1998—1999. The acquisition system SeaBeam2112 was used to acquire data and the processing sequence includes: navigation filter, parameter calibration, correction for transducer draft, correction of sound velocity, data filtering and so on. The cell size of raster grids is ca. 100 m and the vertical resolution is ca. 3‰ of the water depth. The multi-beam bathymetry is utilized to study the morphology, size and shape of the pockmarks and mud volcanoes. Statistical and fitting methods are used to study their distribution features and regional differences according to the pockmarks' width and depth and the mud volcanoes' diameter and height.
The characteristics of the pockmarks and mud volcanoes in different areas vary from area to area apparently, which are shown respectively in the result sections. Compared with the western margin, pockmarks in the northern margin are fewer and smaller with width of no more than 100 m. A few giant pockmarks with widths of 400~1200 m are found in Qiongdongnan Basin. All of them tend to develop on the continental slopes or near the continental shelf break. Pockmarks in the western margin show various shapes in planar view, like circular, elliptical, crescent, elongated and irregular, and have larger size, which usually exceed 1000 m in width and 100 m in depth. Some of them are composited, arranged in a chain or gathered in a group. Some of them grow near canyons or channels, in the soft sediment deformation areas or beside the mud volcanoes. Mud volcanoes with widths more than 100 m widely spread singly or in groups in Southwest Taiwan Basin, Yinggehai Basin and Zhongjiannan Basin. Fitting results reveal that the slopes and coefficients of determination (R2) of pockmarks' fitting curves are different in each area, showing relatively bad linear relationship, however, the pockmarks of all the study areas show a good linear relationship. On the contrary, mud volcanoes in individual areas show good linear relationships, but all of them show a relatively bad linear relationship. Besides, according to the statistics result, a comprehensive pockmark classification scheme is proposed based on (a) their shape in planar view, which includes circular, elliptical, crescent, comet-shape, elongated and irregular pockmarks; (b) their magnitude, which includes small, conventional, giant and mega pockmarks; and (c) their composite pattern, which includes composite pockmarks, pockmark chains and pockmark groups.
Different fitting characteristics of pockmarks in different areas may reveal various seafloor sediments, shallow structural activities, continent slope dip and bottom current and so on. A good linear relationship of mud volcanoes in the same area may indicate that mud volcanoes suffer from minor environmental impact and have a strong coherence of morphologies, fluids components and fluids origin, which are probably different in other regions. Results indicate that the appearance of pockmarks and mud volcanoes are strongly coherent with the active activities of strike-slip faults in southern Taiwan and the western margin in recent ca. 5 Ma. They are widespread with a relatively larger scale in strike-slip faults zones, like Southwest Taiwan Basin, Yinggehai Basin and Zhongjiannan Basin, but fewer and smaller in other extensional basins. Their distribution characteristics which may become important signs of hydrocarbon resources exploration, on one hand may indicate large quantities of fluid escape and on the other hand would indicate that continuous regional tectonic activities are in favor of shallow fluids accumulation and forming reservoirs resulted from deeply buried fluids escaping. |
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| Keywords: | Pockmark Mud volcano Neotectonics Fluid flow South China Sea |
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