中沙海槽盆地构造与沉积作用及其对远端裂陷盆地演化的启示

Tectonics and Sedimentation of the Zhongsha Trough Basin:Implications to the Basin Evolution in Distal Rifting Margin

深水远端裂陷盆地演化是大陆边缘构造研究的热点.中沙海槽盆地位于西北次海盆和西南次海盆之间,是一个临近洋盆的裂陷盆地.根据最新的地球物理资料,揭示了该盆地的沉积层序和构造演化.中沙海槽盆地裂开后期地层厚度约为200~1500 m,可划分为6个地震层序.古近系分布局限,仅限于中沙海槽盆地和中沙南盆地的深凹部位;新近系一般厚为200~1100 m;第四系厚度薄且变化小.中沙海槽盆地主要特征如下:(1)岩浆活动强烈,岩体数量较多,遍布整个盆地,地震剖面上的反射特征表明有侵入型和喷出型两类岩石.重磁异常综合解释表明火成岩成分为中-酸性和中-基性两类;(2)裂陷盆地位于拆离的磁性基底隆起之上,磁性基底北深南浅,埋深在6.0~10.4 km之间;(3)莫霍面埋深在15~24 km之间,地壳由陆向海逐渐减薄、由盆地到岛礁逐渐变厚.中沙海槽盆地通常以犁式正断层为边界断层,其构造变形以伸展构造为主,断层走向主要有NE-SW向和NW-SE向,其中NE-SW向控制了新生代沉积坳陷的发育.

The basin evolution in distal rifting margin has been hotspot in the continental margin scientific planning. Zhongsha trough basin located between the Northwest Sub-Basin and Southwest Sub-Basin is a typical distal rifting basin nearby the ocean basin. In this study, the seismic sequence and tectonic have been unraveled based on the newly collected geophysical data. The basin has been filled with sediments of 200-1 500 m in thickness and 6 identified seismic sequences. Eogene sequence is limited at trough center;while Neogene sequence covered in the whole basin with thickness of 200-1 100 m. Quaternary sedimentary layer is thin hemipelagic deposits. The distal basin has three characters as follows.(1) Intensive magma activity occurred in the whole basin. It was characterized by a large amount of igneous intrusion and eruption on the seismic sections.(2) the rifting basin located over acoustic basement. It has magmatic feature and varied at 6.0-10.4 km buried depth.(3) Buried depth of Moho varies between 15 and 24 km. It is thinner seaward and thick to coral reefal islands. The tectonic deformation is characterized by rifting structures which included NE-SW and NW-SE trending faults, of which the NE-SW striking faults controlled the Cenozoic depression development.