LATE JURASSIC AGE FOR THE MOROKWENG IMPACT STRUCTURE, SOUTHERN AFRICA

A roughly 70 km diameter circular feature buried beneath the Kalahari sands in South Africa is revealed on regional aeromagnetic maps. Boreh oles drilled into the centre of the structure intercept a similar to 2 50 m thick sheet of quartz norite, interpreted as an impact melt, whic h overlies brecciated and shock; metamorphosed basement granite, Zirco ns recovered from the quartz norite, yield U-Pb ages of 145 +/- 0.8 Ma , and biotites provide Ar-Ar ages of 144 +/- 4 Ma, These data provide strong evidence for the occurrence of a Late Jurassic impact crater (t he Morokweng impact structure) similar to 100 m beneath the surface.