THE AGE OF THE SALTPAN IMPACT CRATER, SOUTH-AFRICA

The 1.13-km-diameter Pretoria Saltpan impact crater is located about 4 0 km NNW of Pretoria, South Africa. The crater is situated in 2.05 Ga old Nebo granite of the Bushveld Complex that is locally intruded by a bout 1.3 Ga old volcanic rocks. In 1988, a borehole was drilled in the center of the crater. At depths >90 m, breccias were found that conta ined minerals with characteristic shock-metamorphic features, thus con firming the impact origin of the crater. Fragments of impact glass wer e recovered from the melt breccias and several hundred sub-millimeter- sized glass fragments were subjected to fission track analysis. The me asurements were complicated by the inhomogeneous composition of the im pact glasses, but analysis of a large number of tracks yielded an age of 220 +/- 52 ka for the Saltpan