MOROKWENG IMPACT STRUCTURE, NORTHWEST PROVINCE, SOUTH-AFRICA - GEOPHYSICAL IMAGING AND SHOCK PETROGRAPHIC STUDIES

The existence of a large, near-circular, structure centred on the area around Morokweng (23 degrees 32'E/26 degrees 31'S) in the Northwest P rovince of South Africa, and possibly extending into southern Botswana , is inferred from aeromagnetic and gravity data. Results of surface g eological studies support earlier suggestions that this feature could represent an impact structure. Samples from an autochthonous ironstone breccia exposure about 47 km to the west of the centre of this struct ure, and several samples of allochthonous quartzite from south of the central part of the structure, contain shock metamorphosed quartz with impact diagnostic planar deformation features (PDFs). The geophysical evidence is suggestive of an original size of this impact structure o f at least 70 km, but several annular anomalies outside of the study r egion could be interpreted as indicating a diameter of 300-340 km. The age of this structure is only loosely constrained, but is believed to be younger than the 2.25-2.5 Ga Transvaal Supergroup.