南海莺歌海盆地形成机制的物理模拟

ANALOGUE MODELING OF THE FORMATION MECHANISMFOR THE YINGGEHAI BASIN,SOUTH CHINA SEA

莺歌海盆地位于印支板块和华南板块的拼接带、红河断裂带的海上延伸带上，构造演化十分复杂。由于盆地沉积厚度巨大，泥流体底辟发育，地震勘探难以直接揭示盆地内部深层的构造面貌，因而对盆地形成与构造演化的认识存在明显的分歧。利用常用的三维比例沙箱模型，对盆地的形成机制进行了物理模拟。结果表明莺歌海盆地的形成可分3个阶段：自50Ma B．P．或更早开始，在沿红河断裂带带伸展分量的左旋错动和印支地块的顺时针旋转的联合应力场作用下，形成了莺歌海盆地的断陷格架；大约21Ma B．P．之后在纯左旋错动阶段叠加了压扭应力场，形成了盆地西北部的反转构造；约 5Ma B．P．之后发生了右旋错动，带来了盆地内新一轮的快速沉降。根据盆地内最老和最新的沉积中心之间的距离，推测沿红河断裂带的左行位错约200km。

The Yinggehai Basin lies on the suture zone of the Indochina and South Chinablocks, and the offshore extension of the Red River Fault zone. The basin is characterizedby huge sediments and active mud--fluid diapirs. The deep crustal structures of the basinhave not been determined, and the formation and evolution of the basin is still controver-sial. We used a 3--D scaled sandbox model in analogue modeling to study the formationmechanism of the basin. Results indicate that the basin experienced three stages of dy-namic history. Since 50 Ma B. P. or earlier the basic structural framework of the basinwas formed under the stress field resulted jointly by the left--lateral wrench movementwith extensional compoent and the clockwise rotation of the Indochina block. After ca.21 Ma B. P. the rotation stopped while the left--lateral movement continued. A stressfield became transcompressional, and structural conversion occurred in the NW portionof the basin. At ca. 5 Ma B. P. the movement shifted to right--lateral, which triggered anew phase of strong subsidence in the basin. Bassed on the distance between the o1destand youngest sedimentary centers,a 200 km of net leftlateral displacement within thebasin is estimated.