中国东部海区地球物理调查及重磁场特征

GEOPHYSICAL SURVEY IN EASTERN CHINA SEAS AND THE CHARACTERISTICS OF GRAVITY AND MAGNETIC FIELDS

中国海洋地质调查始于20世纪50年代,大致分为创业阶段、起步阶段、发展阶段、全面发展阶段和蓬勃发展阶段,经过多年的地质与地球物理调查,获取了大量的地质地球物理资料。该区磁场强度一般为±200nT,局部达到±500nT以上,呈NE、NNE向作带状分布,局部异常走向不一,类型多变。空间和布格重力异常总体走向为NE向,陆区以负异常为主,海区主要表现为正异常,空间重力异常值总体上为-45^+100mGal,局部异常值可达+200mGal以上;布格重力异常极小值为-140mGal,极大值可达+440mGal,局部地区分布高值异常圈闭。根据重、磁异常的幅值高低、形态展布和区域变化等特征,将重、磁异常各自划分为华北-渤海异常区、山东半岛-北黄海异常区等9个异常区,重磁场特征充分展示了中国东部海区东西分带、南北分块的构造格局。

Marine geophysical investigation in China started from 50＇s of the last century.It could be roughly divided into the starting-up stage,early stage,developing stage,rapid developing stage and accelerated developing stage.A large number of high-resolution geological and geophysical data have been acquired by the surveys in the past years.With regard to the magnetic data,the background of magnetic anomalies is± 200 nT,with some anomalies higher than±500nT occurring in some local areas.Most of the anomalies extend in NE or NNE direction in a band pattern.However,some anomalies vary in both types and distribution patterns.Free air and Bouguer gravity anomalies are also showing a NE distribution pattern.In a general view,negative anomalies prevail in land,whereas the sea is dominated by positive anomalies.The intensity of free air gravity anomalies normally vary in the range of-45and＋100mGal,with some of anomalies higher than＋200mGal in local areas.The intensity of Bouguer gravity anomalies change between-140 and ＋440mGal.According to the intensity of gravity and magnetic anomalies,in combination with the characteristics of geomorphology,we may divide the region into nine areas,such as the North China-Bohai magnetic anomaly area and Shandong peninsula-north Yellow Sea anomaly area.The distribution pattern of＂zoning in east-west direction and blocking in north-south direction＂is rather obvious.