南海南部地壳结构的重力模拟及伸展模式探讨  

Crustal Structures Inferred from Gravity Modeling and Stretching Modelin the South of South China Sea

作　　者：程子华[1,2] 丁巍伟[1,2] 董崇志[1,2] 方银霞[1,2] 唐勇[1,2] 

机构地区：[1]国家海洋局第二海洋研究所,杭州310012 [2]国家海洋局海底科学重点实验室,杭州310012

出　　处：《高校地质学报》2014年第2期239-248,共10页Geological Journal of China Universities

基　　金：国家自然科学基金项目(41376066);国家海洋局基本科研业务费专项(JT1202);海洋公益性行业科研专项(201205003)联合资助

摘　　要：对南海南部地壳结构研究有助于揭示南海完整的演化历史。本研究对南海南部获取的两条多道地震剖面进行了地震解释，并对重力数据进行了壳幔密度反演。其中NH973-1测线始于南海西南次海盆，覆盖了南沙中部的北段；NH973-2测线始于南海东部次海盆，穿越礼乐滩东侧。反演结果显示，莫霍面埋深在海盆区10-11 km，陆缘区15-21 km左右，洋壳向陆壳莫霍面深度迅速增加。海盆区厚度在6-7 km，为典型的洋壳；陆缘区地壳厚度在15-19 km，为减薄型地壳。进一步研究表明（1）在西南次海盆残余扩张脊之下，莫霍面比两侧略深；（2）在礼乐滩外侧海盆区有高值重力异常体，推测为洋壳与深部岩浆混合的块体；（3）南沙区域上地壳存在高密度带，且横向上岩性可能变化。南海南部陆缘未发现有下地壳高速层，有比较一致的构造属性和拉张样式，为非火山型陆缘。我们对两条测线陆缘的伸展因子进行了计算，发现上地壳脆性拉伸因子与全地壳拉伸因子存在差异，其陆缘的拉张模式在纵向上是不均匀一的。Studies on the crustal structures of the continental margin could contribute our understanding of the evolutionary history of the South China Sea （SCS）. With gravity modeling works based on two newly acquired composite geophysical profile starts in the south of the South China Sea, we reconstruct the crustal structures in this area and discuss the stretching model. NH973-1profilestarts from the SW sub-basin of the SCS, and crosses the northern part of the central Nansha region. The NH973-2 profile lies in the more east and runs across east of the Reed Bank. Gravity modeling shows that the Moho depth is about 10-11km under the sea basin, and 15-21km under the southern margin. A sharp change from the sea basin to the continental margin could be observed. The thickness of the crust in the sea basin is between 6-7km, acting as typical oceanic nature. The crust in the Nansha region is extremely attenuated with thickness between 16 and 19km. Detailed analyses show that （1） a deeper Moho exists under the relic spreading ridge of the SW sub-basin;（2） a gravity high in the E sub-basin closed to the Reed Bank, which might be caused by the mixing of oceanic crust and deep magma; （3） the upper crust of Nansha region may have a high density zone, and on the lateral lithological features changes laterally. The crustal structures in the Nansha region and Reed Bank act similar features, and no high velocity layer has been found under either area. We suppose that the southern margin of the SCS should have experienced magma-poor rifting. Stretching factors were calculated along two profiles. The results indicate that fault-related stretching factors were different from the whole crust stretching factor. It suggested that the southern margin might have experienced non-uniform extension.

关 键 词：重力模拟 南海南部 非火山型 拉伸因子 

分 类 号：P631[天文地球—地质矿产勘探]