Vredefort Ring Structure: Meteorite Impact Scar?

Abstract

The peerless Vredefort Ring structure of South Africa defies rational interpretation by tectonic, volcanic, or magmatic forces. Following the heretical opinion of Boon, Albritton, and Daly, it is suggested to be a meteorite impact structure or "astrobleme." Using an impact velocity of 20 km/sec, it was found that an asteroid 2.3 km. in diameter would provide the 6 x 1028 ergs (1.4 million megatons TNT-equivalent) needed to create the original crater 40 km. across and roughly 16 km. deep. An impact event adequately explains: (1) the apparent impulse direction which was radially outward from the center; (2) the shatter cones as shock-induced; (3) the bilateral symmetry as owing to an oblique impact; (4) the upturned and overtilted 16-km. thick collar as the effect of radial forces spreading out from the explosion focus; (5) the pressure and thermal metamorphism of the sedimentary collar as shock wave-induced; (6) the intensive fracturing and microshearing of rock with little relative displacement as shock wave-induced; (7) the pseudotachylite as a "shock impactite" produced by overpressures in excess of 105 bars; and (8) the granophyre dikes as injected crater-lining "impactite." The uplifted granite plug now filling the original crater was caused by a combination of elastic rebound and isostatic forces. It would seem that, at Vredefort, an impact event transpired equivalent to the formation of Copernicus or Tycho on the moon.