GEOPHYSICAL SIGNATURE OF THE PRETORIA SALTPAN IMPACT STRUCTURE AND A POSSIBLE SATELLITE CRATER

The genesis of the 1.13-km-diameter Pretoria Saltpan crater has long b een the focus of a controversy. Its origin has been explained by eithe r meteorite impact or ''cryptoexplosive'' volcanic activity, but it wa s recently confirmed through detailed petrographic and chemical analys is of a breecia layer forming part of the crater fill, that the crater was formed by impact. As the limited previous geophysical work failed to support an impact origin, a more detailed gravity and magnetic stu dy was conducted. A possible 400-m-diameter circular crater located 3 km to the southwest of the main crater was also investigated with geop hysical methods, including resistivity, seismics and ground-probing ra dar. The gravity signature of the main crater is compatible with that of a simple impact crater and the magnetic signature (no magnetic anom aly could be detected) rules out the possibility of a central magnetic volcanic body below the crater-fill sediments. The results for the po ssible twin or satellite crater are inconclusive. As it is the only su ch feature in the entire region it should not be overlooked. A drillin g program may reveal interesting results.