CAJ | 학술논문

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。
대남해남부지각결구연구유조우게시남해완정적연화역사。본연구대남해남부획취적량조다도지진부면진행료지진해석，병대중력수거진행료각만밀도반연。기중NH973-1측선시우남해서남차해분，복개료남사중부적북단；NH973-2측선시우남해동부차해분，천월례악탄동측。반연결과현시，막곽면매심재해분구10~11 km，륙연구15~21 km좌우，양각향륙각막곽면심도신속증가。해분구후도재6~7 km，위전형적양각；륙연구지각후도재15~19 km，위감박형지각。진일보연구표명(1)재서남차해분잔여확장척지하，막곽면비량측략심；(2)재례악탄외측해분구유고치중력이상체，추측위양각여심부암장혼합적괴체；(3)남사구역상지각존재고밀도대，차횡향상암성가능변화。남해남부륙연미발현유하지각고속층，유비교일치적구조속성화랍장양식，위비화산형륙연。아문대량조측선륙연적신전인자진행료계산，발현상지각취성랍신인자여전지각랍신인자존재차이，기륙연적랍장모식재종향상시불균균일적。
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.