南海共轭陆缘新生代碳酸盐台地对海盆构造演化的响应

Response of Cenozoic Carbonate Platform on Tectonic Evolution in the Conjugated Margin of South China Sea

南海新生代碳酸盐台地分布面积广、厚度巨大,但大部分已经淹没,成为淹没碳酸盐台地,它们孕育着南海海盆演变的重要信息.南海碳酸盐台地伴随着南海陆缘张裂而发育,最初主要发育在两个共轭陆缘伸展地块的构造高地.南海经历了大陆边缘伸展、岩石圈减薄和地幔剥露等过程,始新世到早渐新世的第二期NE-SW向扩张,形成了破裂不整合面,随之发生了晚渐新世至早中新世的海底扩张,形成中央海盆.构造沉降提供了台地生长的可容纳空间,构造掀斜作用、断裂作用和前陆盆地前沿挤压褶皱的迁移控制了台地各单元厚度、沉积相和地震反射终止特征在横向上的变化,构造控制的相对海平面的变化控制了不同级序生物礁碳酸盐台地的沉积旋回,而后期加速沉降导致碳酸盐台地淹没.

Cenozoic carbonate platforms of great thickness are widely developed in the South China Sea,most of which have been drowned since the Late Cenozoic and named drown carbonate platform accordingly.The carbonate platforms in the South China Sea are unique and rich in tectonic evolution information.The carbonate platforms were developed by the rifting processes,and were initiated on the faulted block shoulder in the conjugated rifting margin.The South China Sea margin experienced rifting,thinning,and mantle exhumation.The Eocene and Early Oligocene NE-SW direction rifting led to breakup unconformity.Then Central Ocean Basin occurred during Late Oligocene-Early Miocene sea floor spreading.Tectonic tilt,faulting and migration of compressive fold in the front of foreland basins controlled the distribution,thickness and seismic reflection horizontal variation.Tectonic induced relative sea level changes controlled the sedimentary cycles of carbonate platforms.And more,later rapid subsidence in Late Miocene induced the drowning of most carbonate platforms.