南沙中部海域北康·曾母盆地重磁异常特征及解释

通过对南沙中部海域北康、曾母盆地重、磁资料的定量计算、定性解释,认为空间重力异常主要受浅部地质因素影响,空间重力异常的高低间接地反映了海底地形起伏变化、新生代沉积层厚度大小、沉积岩密度变化以及基底的坳、隆等特征;磁力异常资料通过预后处理及反演计算,推测北康、曾母盆地新生代火成岩以中酸性-中基性岩为主,磁性基底与声波基底基本一致,可划分为2处坳陷及3处隆起;北康、曾母盆地位于减薄的大陆壳上,莫霍面深度约21～2 km.重、磁资料综合解释结果为沉积盖层构造分区、基底断裂推断及火成岩岩性识别提供依据.

CHARACTERISTICS AND INTERPRETATION OF GRAVITY AND MAGNETIC ANOMALIES IN THE BEIKANG ZENGMU BASIN OF CENTRAL NANSHA ISLANDS

Through quantitative calculation and qualitative interpretation of gravity and magnetic data collected from the Beikang Zengmu basin of central Nansha Islands, it is demonstrated that the gravity anomalies are mainly influenced by shallow geological factors, that the gravitational high and gravitational low indirectly reflect the topographical features of the sea bed, the thickness of Cenozoic sediments, the density variation of sediments and the subsidence or uplifting of the basin. The conclusion that Cenozoic igneous rocks of the Beikang Zengmu basin are mainly composed of acidic intermediate basic rocks is based on the disposition and inverse calculation of magnetic data. The magnetic basement is basically consistent with the acoustic basement, and can be divided into two depressions and three upwarped zones. the Beikang Zengmu basin lies on the weakened continental crust with Moho thickness of about 21～26 km.The gravity and magnetic interpretation can serve as basis for the tectonic division of the basement and the recognition of igneous rocks.