Access

You are not currently logged in.

Access your personal account or get JSTOR access through your library or other institution:

login

Log in to your personal account or through your institution.

If you need an accessible version of this item please contact JSTOR User Support

Vredefort Ring Structure: Meteorite Impact Scar?

Robert S. Dietz
The Journal of Geology
Vol. 69, No. 5 (Sep., 1961), pp. 499-516
Stable URL: http://www.jstor.org/stable/30056197
Page Count: 20
  • Read Online (Free)
  • Download ($19.00)
  • Cite this Item
If you need an accessible version of this item please contact JSTOR User Support
Vredefort Ring Structure: Meteorite Impact Scar?
Preview not available

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.

Page Thumbnails

  • Thumbnail: Page 
499
    499
  • Thumbnail: Page 
500
    500
  • Thumbnail: Page 
[unnumbered]
    [unnumbered]
  • Thumbnail: Page 
[501]
    [501]
  • Thumbnail: Page 
502
    502
  • Thumbnail: Page 
[unnumbered]
    [unnumbered]
  • Thumbnail: Page 
[503]
    [503]
  • Thumbnail: Page 
504
    504
  • Thumbnail: Page 
505
    505
  • Thumbnail: Page 
506
    506
  • Thumbnail: Page 
507
    507
  • Thumbnail: Page 
508
    508
  • Thumbnail: Page 
509
    509
  • Thumbnail: Page 
510
    510
  • Thumbnail: Page 
511
    511
  • Thumbnail: Page 
512
    512
  • Thumbnail: Page 
513
    513
  • Thumbnail: Page 
514
    514
  • Thumbnail: Page 
515
    515
  • Thumbnail: Page 
516
    516