UPDATED BASEMENT MAP FOR CENTRAL MALAWI DETERMINED FROM GRAVITY AND MAGNETIC DATA

This study aimed at updating the basement of central Malawi using magnetic and gravity data since the current basement complex for central Malawi map has missing features that have been concealed by the soils and sedimentary cover that made it difficult for the mapping of those lithologies. With the use of geophysical techniques to map out these features has made it possible to deduce these concealed features. This study has used the available data set of high resolution aeromagnetic data that was obtained from geological survey department of Malawi from the data that was obtained in 2013-2014 by high resolution geophysical survey of Malawi carried out by sanders geophysics limited jointly funded by European Union and World Bank. And the satellite global gravity model EIGEN-6C4 data that was obtained in bouger anomaly. The datasets have been enhanced and calculated to produce magnetic susceptibility map and density distribution map from magnetic data and gravity data respectively. The magnetic susceptibility map and density distribution map were changed to continuous colour scheme maps ranging from low values to high values of magnetic susceptibility and densities of different lithologies. Then these colour scheme maps of magnetic susceptibility and density distribution were fused to create apparent physical properties map. The colour scheme approach was used to demarcate different regions with different values of magnetic susceptibility and density with four end member colours. Where HMHD represented regions with high magnetic and high density rocks, LM-HD represented low magnetic and high density rocks, HM-LD represents high magnetic and low density rocks and LM-LD represents low magnetic and low density rocks.This apparent physical properties map was then fused with existing geological map to show different geological features that were obtained from geophysical methods. In so doing the concealed lithologies has been updated showing the occurrence, orientation as well as the geotechnical boundaries between different rocks.