中国地区MAGSAT卫星标量和矢量磁异常图

SCALAR AND VECTOR MAGNETIC ANOMALY MAPS FOR CHINA DERIVED FROM MAGSAT DATA

使用MAGSAT卫星资料,编绘中国及邻近地区的卫星磁异常图(10°N—60°N,70°E—140°E)。为了提取地壳异常场,必须从观测资料中消除主磁场、磁层场,感应场和电离层场。本文选用GSFC(12/83)地磁场模型,消除主磁场,磁层场和感应场。为了进一步消除电离层场的影响,改善相邻轨道磁异常的一致性,用纬度的二次多项式拟合每一条轨道的初始地壳异常,并从初始地壳磁异常值减去这一拟合值,从而获得最后的地壳异常值(△X,△Y,△Z,△F)。把研究地区分成1°×1°的网格,将每个网格内的磁异常进行平均,以获得网格中心点的异常值。根据这些网点值绘制中国及邻近地区的卫星标量和矢量磁异常图。等值线间隔为2nT。为了检验卫星磁异常图的可靠性,将卫星资料分成黎明组、黄昏组和联合组,分别进行处理和绘制卫星磁异常图。结果表明:根据上述资料绘制的卫星磁异常图有很好的一致性。中国地区的卫星磁异常值位于—10nT—10nT。卫星磁异常与区域构造特征有较好的一致性;塔里木地台、扬子地台和中朝地台是正磁异常区,西藏高原是负磁异常区。卫星磁异常反映出下地壳磁化强度的横向不均匀性。

The Magsat Investigator-B magnetic tapes are the source of data for this study.The lati-tuhe and longitude ranges of data are from 10°N to 60°N and 70°E to 140°E.In order to get the crustal anomaly field,the main field,magnetospheric,ionospheric and induction fields from the Magsat data must be subtracted.The GSFC (12/83) model is used to correct the internal field,external field and induction field.In order to improve pass to pass consistency,the 2nd-order polynomial in latitude is used to fit the crustal anomaly field for each pass,and subtract the fitted values from the crustal anomaly field to get the final crustal anomaly field.The region studied is divided into cells,the size of each cell is one degree in latitude and longitude.The value of the anomaly field at the center of each cell is taken as the mean values of the data falling into the cell.Based on hte grid point values,the contour maps are produced.They include: 1.The X,Y,Z and F anomaly maps derived from dawn data only;2.The X,Y,Z and F anomaly maps derived from dusk data only;3.The X,Y,Z and F anomaly maps derived using dawn and dusk data combined.The contour interval is 2nT.It is considered that the consistency between the dawn and dusk maps is good.The satellite magnetic anomalies in and near China are between-10nT and 10nT.The magnetic anomalies show good correlation with the regional tectonic features of China: Pre-Cam-brian cratons such as Tarim,Yangtze and Sontliao Cratons are positive anomaly areas.The Tibet plateau is negative anomalp area.The satellite anomalies represent the lateral variations in the magnetization of the lowe crust.