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

The 2-D spectral analysis of gravity and topography data has been used to identify structural trends of recognized geological entities within the tectonic provinces of South Africa. The mean amplitude of the spectra within very thin rings, taken to have the same mean wavenumber, is subtracted from the total spectrum to give the non-isotropic component. This component of the spectrum reflects more of the heterogeneity of the data and is exploited to produce trends. These results are consistent 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 in this area crustal mass distribution is not correlated with surface relief. No dominant structural trend was identified in the Witwatersrand basin. It can be concluded from these findings that this technique can be successfully applied to various data sets, which reflect different physical properties and hence assist in geological interpretation, regardless of the scale.