南海东南部陆缘Nido灰岩发育特征及其构造控制因素

Development Characteristics of Nido Carbonate Platform and Its Tectonic Controls in the Southeast of South China Sea Margin

南海东南部陆缘发育一套晚渐新世-早中新世碳酸盐岩(Nido灰岩)与南海海底扩张历史吻合.为系统了解Nido灰岩构造控制因素,基于大量钻井、拖网和地震资料,刻画碳酸盐岩沉积相特征和时空分布规律,分析构造变形对其控制作用.结果显示:Nido灰岩呈大规模连片分布在研究区东北至西南部.以乌鲁根断裂为界,东北部灰岩呈北西倾向,与早渐新世岩石圈破裂形成的断块高点和扩张阶段较弱的构造活动有关;西南部灰岩呈东南倾向,受晚渐新世伸展断陷形成的构造高点和早中中新世南沙地块板片挠曲形成的构造前隆迁移作用控制.碳酸盐岩台地主要发育期与海底扩张时间吻合,具有区带性,反映南海穿时破裂过程和南部陆缘俯冲-碰撞过程的横向差异和不均一性.

The development characteristics of the carbonate platform and its tectonic controls in the southeast of South China Sea margin are still in debate. Based on wells, dragnets, and large number of 2 D seismic data, we interpreted structural and stratigraphic data of the seismic profiles and described the development characteristics and temporal and spatial distribution of carbonate platform. Then the tectonic deformation, subsidence history, and fault activity with the developments of different carbonate platforms were analyzed. The results show that the large-scale contiguous Nido carbonate platform is mainly developed on the tectonic high points of the tilting fault block and the tectonic front uplift, distributed in the northeast to southwest of the study area. Bounded by the Ulugan fault, the Nido platform in the northeast is northwest trending, which is mainly controlled by factors such as the height of the tilting fault block formed by the extensional fault depression, the weak tectonic activity in the expansion stage, and the lack of sediments supply. The Nido platform in the southwest of the Ulugan fault trends to southeast, and it is mainly the structural high point formed by the extensional fault depression in the Late Oligocene, and the relative uplift caused by the flexural forebulge in the Late Oligocene-Early Miocene is related to the migration of the pre-tectonic uplift and sea level changes. The main development period of the carbonate platform coincides with the expansion time of the seafloor and has obvious banding. This feature is related to the pre-existing tectonic background and evolution process at different tectonic locations,reflecting the diachronous breakup of the South China Sea and discordant subduction-collision process.