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

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.