REGIONAL CRUSTAL TRENDS IN SOUTH-AFRICA FROM THE SPECTRAL-ANALYSIS OFTOPOGRAPHIC AND GRAVITY-DATA

The 2-D spectral analysis of gravity and topography data has been used to identify structural trends of recognized geological entities withi n the tectonic provinces of South Africa. The mean amplitude of the sp ectra within very thin rings, taken to have the same mean wavenumber, is subtracted from the total spectrum to give the non-isotropic compon ent. This component of the spectrum reflects more of the heterogeneity of the data and is exploited to produce trends. These results are con sistent with known structural trends, but also reveal new trends. Some trends, identified on the Kaapvaal craton using gravity data, are at variance with those obtained from the topography. This suggests that i n this area crustal mass distribution is not correlated with surface r elief. No dominant structural trend was identified in the Witwatersran d basin. It can be concluded from these findings that this technique c an be successfully applied to various data sets, which reflect differe nt physical properties and hence assist in geological interpretation, regardless of the scale.