珠江口盆地深水区晚中新世以来构造沉降与似海底反射(BSR)分布的关系

摘要

2007年中国在南海北部神狐海域通过钻探首次获得天然气水合物样品,证实了珠江口盆地深水区是水合物富集区.通过对珠江口盆地深水区构造沉降史的定量模拟研究,发现晚中新世以来区内构造沉降总体上具有由北向南、自西向东逐渐变快的演化趋势；从晚中新世到更新世,盆地深水区经历了构造沉降作用由弱到强的变化过程:晚中新世(11.6～5.3 Ma),平均构造沉降速率为67 m/Ma；上新世(5.3～1.8 Ma),平均构造沉降速率为68 m/Ma；至更新世(1.8～0 Ma),平均构造沉降速率为73 m/Ma.而造成这些变化的主因是发生在中中新世末—晚中新世末的东沙运动和发生在上新世—更新世早期的台湾运动.东沙运动(10～5 Ma)使盆地在升降过程中发生块断升降,隆起剥蚀,自东向西运动强度和构造变形逐渐减弱,使得盆地深水区持续稳定沉降；台湾运动(3 Ma)彻底改变了盆地深水区的构造格局,因重力均衡调整盆地深水区继续沉降,越往南沉降越大.将似海底反射(BSR)发育区与沉降速率平面图进行叠合分析,发现80％以上的BSR分布趋于构造沉降速率值主要在75 ～ 125 m/Ma之间、沉降速率变化迅速的隆坳接合带区域.%The samples of gas hydrate have been successfully obtained by drilling in the Shenhu area of northern South China Sea, it is confirmed that the Pearl River Mouth Basin is a gas hydrate-rich area. By means of quantitative basin modeling research of tectonic subsidence history of deep water area in Pearl River Mouth Basin, tectonic subsidence has been generally characterized by acceleration from north to south and from west to east in the research area since the Late Miocene. From the Late Miocene to Pleistocene , deep water area in the basin experienced the variation process of tectonic subsidence effect that was from weak to strong; The average tectonic subsidence rate was 67 m/Ma in the Late Miocene (11.6 ~ 5. 3 Ma) , the average tectonic subsidence rate was 68 m/Ma in the Pliocene (5. 3 -1.8 Ma) , and the average tectonic subsidence rate was 73 m/Ma in the Pleistocene (1.8 ~0 Ma). Moreover, the major reasons which causing these changes were Dongsha tectonic event from the end of the Middle Miocene to the end of the Late Miocene and Taiwan tectonic event from the Pliocene to the Early Pleistocene; Dongsha tectonic event (10 ~ 5 Ma) makes fault block uplifting and sagging, rise area eroding, and waning of movement intensity and structural deformation from east to west, which caused stable subsidence of deep water area in the basin; Taiwan tectonic event (3 Ma) thoroughly changed the tectonic framework of deep water area in the basin, which kept on subsiding and was subsiding more southward because of gravity balance. Overlaying the developed areas of BSR and plane map of tectonic subsidence rate, it was discovered that more than 80% Bottom Simulating Reflector ( BSR) tend to be distributed in the transfer zone between uplift and depression that the average tectonic subsidence rate ranged from 75 m/Ma to 125 m/Ma and changed rapidly.