中南-礼乐断裂带在南海海盆北部的时空展布与深部结构

The Temporal-Spatial Distribution and Deep Structure of the Zhongnan-Liyue Fault Zone in the North of the South China Sea Basin

中南-礼乐断裂带是协调南海各次海盆扩张的重要断裂.深入研究中南-礼乐断裂带时空展布和深部结构对于认识南海海盆多期次海底扩张和构造演化具有重要意义.本文主要基于深反射多道地震的精细剖析,结合重力、磁力与地形等地质与地球物理资料,揭示了中南-礼乐断裂带在南海海盆北部的时空展布特征、内部构造形变及其深部结构特征.结果表明:中南-礼乐断裂带在西北次海盆与东部次海盆之间宽约25~35 km,北延于珠江海谷西侧(18.7°N,115.5°E),南消失于中沙地块东北侧(17.2°N,116.0°E),主要呈NNW向延伸.该断裂带的主控断裂沿大型海山和侵入岩体分布,主要发育时期是渐新世至早中新世,中中新世至晚中新世为继承性活动,其内部断裂对早中新世及以前的地层具有控制作用,表现为正断层.深部结构上,中南-礼乐断裂带两侧Moho面埋深不一,两侧次海盆的沉积厚度和洋壳厚度存在明显差异,表明该断裂带至少是一条地壳级断裂,甚至可能是岩石圈级断裂.

The Zhongnan-Liyue fault zone(ZLFZ) is an important fault zone that coordinated the spread of the sub-oceanic basins in the South China Sea(SCS). In-depth study of the temporal-spatial distribution and deep structures of the ZLFZ is of great significance for understanding the multi-phase spread and tectonic evolution of the SCS Basin. Based on the geological and geophysical data including multi-channel seismic, gravity, magnetic and topographic data, this study reveals the temporal-spatial distribution, internal structural deformation and deep structures about the north segment of ZLFZ in SCS basin. The results show that(1) the width of the ZLFZ between the northwest sub-basin and the eastern sub-basin is about 25-35 km. It starts from the west side of the Zhujiang Sea valley(18.7°N, 115.5°E) and disappears at the northeast of Zhongsha bank(17.2°N, 116.0°E), and is mainly distributed in the NNW direction. The main fault of the ZLFZ is distributed along the seamounts ridge and intrusive body.The faults are mainly developed in the early stage, which are normal faults.(2) The ZLFZ was mainly developed in Oligocene to Early-Miocene and Mid-Miocene to Late-Miocene, the development was mainly inherited.(3) In the deep structures, there are not only different burial depths of the Moho on the west and east sides of the ZLFZ, but also different sedimentary thickness and oceanic crust thickness in the northwest sub-basin and eastern sub-basin. It is speculated that the ZLFZ is at least a crustal-level fault, which may even break through the lithosphere.