南沙地块南薇隆起区的地震反射特征和结构单元划分

SEISMIC REFLECTION CHARACTERISTICS OF NANWEI UPLIFT ZONE IN NANSHA AND THEIR APPLICATION TO STRUCTURAL UNIT DIVISION

南薇隆起区地处南沙地块西北部,紧邻西南次海盆,周围发育大量陆缘裂解盆地。裂陷盆地拥有丰富的油气资源。地块经历了中生代末期至古近纪裂谷拉张,并随晚始新世的海底扩张向南漂移至现今位置。结合区域以往地震剖面和钻井数据,分析了2013年中科院南海海洋研究所"实验2号"采集的高分辨率单道地震数据(Nan-1),总结了南薇隆起区的地震反射特征。认为南薇隆起区主要由南部裂陷下沉带和北部埋藏火山隆起带两个结构单元组成。从北到南,埋藏火山隆起带跨越约63km的范围,裂陷下沉带跨越约58km的范围。地震剖面清晰地揭示了该区向海盆侧隆起且在SE向成带的特征。南薇区具有拉张背景,其形成与演化主要是与西南次海盆的扩张作用,以及南沙地块与婆罗洲地块的碰撞作用等有关。自上新世以来,整个南薇隆起区进入构造活动相对稳定阶段,地壳稳定性较好。

A large number of continental margin rifting basins are well developed on the Nanwei uplift of Nansha Waters, which bears great oil and gas potentials. The region experienced a complex evolutionary history in Cenozoic period, including extensional rifting from Late Mesozoic to Paleogene and seafloor spreading in Late Eocene. A high-resolution single-channel seismic line Nan-l, acquired in the Nansha by the trial vessel ＂Shiyan 2＂ of the South China Sea Institute of Oceanology in 2013, is interpreted and ana- lyzed in this study. As well, some previous seismic profiles and drilling data are studied. The seismic re- flection characteristics of the Nanwei uplift in the southern margin are summarized and outlined briefly. Results show that the Nanwei uplift zone is mainly composed of two structural units, the southern belt of subsidence and the northern belt of buried volcanic uplift. Compared to the previous reflection seismic data in this area, some main seismic reflection layers are divided. The belt of buried volcanic uplift is about 63 km wide, and the neighboring subsidence belt 58 km wide both in SE direction. The distribution of sporad- ic epicenters stronger than 4 magnitude earthquakes suggest that the entire Nanwei uplift is still a relative- ly stable tectonic body since Pliocene.