南海北部陆缘地壳结构及其伸展破裂过程的差异性  

Differences in continental crust structure and its extensional fracture processin northern South China Sea

作　　者：郑金云 代一丁 刘军 庞雄 任建业 董明 ZHENG Jinyun;DAI Yiding;LIU Jun;PANG Xiong;REN Jianye;DONG Ming(Shenzhen Branch,CNOOC,Shenzhen 518054,Guangdong;College of Marine Science and Technology,China University of Geosciences,Wuhan 430074,Hubei)

机构地区：[1]中海石油(中国)有限公司深圳分公司,广东深圳518054 [2]中国地质大学海洋学院,湖北武汉430074

出　　处：《长江大学学报（自然科学版）》2022年第3期12-22,共11页Journal of Yangtze University(Natural Science Edition)

基　　金：国家科技重大专项“大型油气田及煤层气开发”(2016ZX05026-003);国家重点研发计划“深海关键技术与装备”(2018YFC0310100)。

摘　　要：系统分析了南海北部地壳岩石圈结构及其新生代伸展变形的差异性,并探讨了其成因机制。基于南海北部陆缘重磁震联合反演所获得的Moho面深度和地壳厚度,发现地壳的伸展薄化具有“南北分带、东西分段”差异,由北向南可分为陆架均匀薄化带(地壳伸展系数β<1.2)、上陆坡楔形薄化带(1.2<β<2)、下陆坡强烈薄化带(β>2)共3个带;而陆缘深水区由东向西以4条NW-SE向基底隐伏断裂带为界可分为5段:台西南盆地陆缘,珠江口盆地陆缘的东段陆缘、中段陆缘、西段陆缘,琼东南盆地陆缘。不同区段地壳薄化程度交替变化,强烈薄化区呈指状向陆延伸,其所对应的沉积盆地断裂样式、充填结构、裂后沉降、岩浆活动等均表现出不同特征。上述差异表明,南海北部陆缘岩石圈在新生代的伸展薄化过程中,显著受控于先存中生代主动陆缘所形成的基底构造格局及其所对应的岩石圈结构差异;在伸展过程中岩浆大量底侵至下地壳,其热效应导致下地壳的韧性增强,进而改变地壳薄化方式,而先存NE-SW向走滑断裂成为伸展过程中岩浆大量底侵至下地壳的通道。依据岩石圈结构差异及其与沉积盆地响应关系,可将南海北部陆缘岩石圈伸展破裂过程总结为自上而下伸展破裂模式、自下而上伸展破裂模式、似纯剪切快速伸展破裂模式共3种模式。不同伸展破裂模式下,其所对应的裂陷期沉积盆地规模、岩浆改造程度均具有明显差异,导致勘探潜力及勘探策略的不同。The differences of crustal lithosphere structure and Cenozoic extensional deformation in the northern South China Sea were systematically analyzed and their genetic mechanisms were discussed in this paper.Based on the depth of the Moho and crustal thickness obtained from the joint inversion of gravity,magnetism and seism in the northern continental margin of the South China Sea,it is found that the extensional thinning of the crust has the difference of“north-south zoning and east-west segmentation”,and can be divided into continental shelf uniform thinning zone(the crustal extension coefficientβ<1.2),wedge-shaped thinning zone on the upper slope(1.2<β<2)and strong thinning zone of the lower slope(β>2)from north to south.The continental margin deep-water area is bounded by four NW-SE basement concealed fault zones from east to west,which can be divided into five segments:the continental margin of Southwest Taiwan Basin,the eastern,middle and western segments of the continental margin of Pearl River Mouth Basin and the continental margin of Qiongdongnan Basin.The degree of crustal thinning in different segments changes alternately,and the strongly thinned area extends to the land in a finger shape.The fault style,filling structure,post-fracture settlement and magmatism of the corresponding sedimentary basins all show different characteristics.Theabove differences indicate that the lithosphere of the northern South China Sea continental margin is significantlycontrolled by the basement tectonic pattern formed by the pre-existing Mesozoic active continental margin and thecorresponding lithospheric structural differences during the Cenozoic extensional thinning process.Secondly,during the extension process,a large amount of magma infiltrates into the lower crust,and its thermal effect leads to theenhancement of the toughness of the lower crust,thus changing the thinning mode of the crust.The pre-existing NE-SW strike slip fault becomes the channel for a large amount of magma underplating to the lower crust dur

关 键 词：南海北部陆缘 深水盆地 地壳结构 地壳伸展破裂模式 差异薄化 

分 类 号：P542[天文地球—构造地质学]