南沙西南海域新生代构造活动特征与盆地演化

南沙海域处于已俯冲消亡的古南海和海底扩张形成的新南海洋盆之间, 其研究对于了解中生代末期以来南海北部陆缘张裂、新南海海底扩张和古南海向南俯冲消亡等构造过程具有重要意义.通过利用平衡剖面反演对该区新生代以来的构造活动和盆地演化进行研究.结果发现, 该区新生代以来的构造活动具有显著的分区性特征, 表现为以区内深大断裂为界, 所分隔的3个块体其构造活动的主导因素和活动阶段性存在差异.南沙块体构造活动的主导因素为NW向应力, 构造活动以中—晚中新世为界前张后压, 具有明显的阶段性; 万安盆地构造活动受万安断裂控制, 构造活动阶段性不明显; 曾母块体构造活动特征与南沙块体类似, 具有明显的阶段性, 但具体表现不同.在此基础上, 将该区主要盆地的演化划分为4个阶段, 即裂陷阶段、同沉积阶段、挤压阶段和区域沉降阶段.其表现又因盆地成因类型而有所不同: 北康盆地裂陷和挤压阶段突出, 沉降阶段缺失; 南薇西盆地裂陷阶段南弱北强; 万安盆地缺少挤压阶段; 曾母盆地则4个阶段均非常明显. 

Cenozoic Tectonics and Basin Evolution in the Southwestern Nansha Sea Area

Nansha Sea area lies between extinct paleo-South China Sea and newly-formed South China Sea (SCS) and its relevant researches are of great importance for understanding the mechanisms of rifting in northern SCS continental margin, seafloor spreading in the new SCS, and southward subduction of the paleo-SCS.This paper studies the Cenozoic tectonics and basin evolution in the area by utilizing balanced section.It is suggested that the Cenozoic tectonics in this area have evident zonality features demonstrated by different dominating factors and tectonic activity stages in the three blocks separated by major faults.The tectonic activities of Nansha block are dominated by NW-striking stress, and are divided into an extension-and compression stage by Mid-Late Miocene.Wan'an basin is controlled by Wan'an Fault, and shows no significant stage feature.Zengmu block displays overall similar tectonic activity characteristics and some differences from Nansha block.Based on these results, evolution of major basin in this area is divided into four stages: rifting-, syn-sediment-, compressing-, and regional subsidence stage.However, evolution differs in different basins: Beikang basin is prominent in the rifting and compressing stage, and is lack of regional subsidence stage; Nanweixi basin rifts strongly in the north and is relatively weak in the south; Wan'an basin is lack of compressing stage; Zengmu basin shows evident four-stage feature.