南海东部次海盆南侧基底结构与沉积特征及其控制因素

Basement and Sedimentary Characteristics and Controlling Factors of the Southern East Sub-basin, South China Sea

南海东部次海盆经历了完整的海底扩张过程,对其进行从北至南、从东到西系统的研究有助于进一步认识南海的演化过程。通过南海东部次海盆3条多道地震剖面的解析,对其基底形态、沉积充填和岩浆活动特征进行研究,首次揭露了南海东部次海盆南侧东西向的沉积-构造特征。结果表明,南海东部次海盆南侧基底主要分为两种类型:一种为崎岖不平、深海丘陵和海山发育,且基底隆起表现为“东高西低”;另一种基底相对平坦,局部有岩浆侵入。两种基底形态受海底扩张速率、板片俯冲挠曲和扩张后岩浆活动等因素综合控制。东部次海盆南部的沉积充填类型主要有3种,受构造、沉积作用和物源供给共同控制,总体上呈现出邻近扩张脊一侧沉积薄、靠南部陆缘一侧沉积厚;东部边缘因构造挠曲等因素,基底构造隆起更强,形成较薄沉积,厚度最小处约160 m。基于沉积-构造-岩浆特征,构建东部次海盆南部海底扩张末期以来(16 Ma至今)的沉积-构造演化模型,对南海形成演化研究具有重要意义。

The east sub-basin(ESB) of the South China Sea(SCS) experienced a complete seafloor spreading process. A systematical study of the ESB is extremely important for a thorough understanding of the evolution of the SCS. This paper studies the basement morphology, sedimentary and magmatic activities of the ESB through interpretation of three multi-channel seismic profiles, and reveals the east-west direction tectonic and sedimentary characteristics of the southern ESB for the first time. The results indicate that the southern ESB has two styles of basement, i.e., the rugged deep-sea hills and seamounts characterized by a westward declining basement uplift, and the relatively flat basement with localized distribution of magmatic intrusions. It is inferred that these two styles of basement are jointly controlled by the seafloor spreading rate, magmatism, and tectonism. Three sedimentary filling types are identified, which are controlled by the tectonic, sedimentation, and provenance. Overall, the deposit is thinner near the fossil spreading ridge and thicker near the southern continental margin. As a result of structural deflection, the basement uplift at the eastern margin was much intensive, and accumulated sediments with thickness of over 160 meters. A tectonic-sedimentary evolution model of the southern ESB was simulated based on the sedimentary-tectonic-magmatic characteristics. The model covers a geological period ranging from 16 Ma to the present, which would be of great significance to the study of the SCS evolution.