Morokweng, South Africa - The Jurassic-Cretaceous boundary impact structure?

Details Morokweng, South Africa - The Jurassic-Cretaceous boundary impact structure? Morokweng, South Africa - The Jurassic-Cretaceous boundary impact structure?

Mar 1997

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997lpi....28..741k&link_type=abstract

Conference Paper, 28th Annual Lunar and Planetary Science Conference, p. 741.

Physics

Geophysics

Republic Of South Africa, Earth Surface, Geophysics, Petrology, Geochemistry, Geochronology, Chondrites, Pyroxenes, Hypervelocity Impact

Scientific paper

The existence of a large, almost circular, subsurface structure in the area around Morokweng, South Africa, was inferred on the basis of gravity and magnetic investigations. Detailed geophysical studies showed the presence of a circular positive magnetic anomaly (up to 350 nT above regional background). This anomaly (the 'Ganyesa Dome') is a central 30-km-diameter near-circular area surrounded by a concentric, magnetically quiet zone 20 km wide, representing the Morokweng Ring Structure. Three drill cores were obtained from near the center of the structure. Preliminary data indicated the presence of melt rocks with high contents of siderophile elements. Our detailed petrographical and geochemical studies proved the presence of a thick layer of impact melt rocks with high abundances of Cr, Ni, Co, and the platinum group elements (PGEs). The PGEs and other siderophile elements are rather homogeneously distributed and the enrichments are consistent with up to 5 percent of a meteoritic (chondritic) component being incorporated in the impact melt. To determine the age of the structure, we extracted zircons from the impact melt. Ion probe dating of these zircons yielded an age of 146.2 +/- 1.5 Ma, which is indistinguishable from that of the Jurassic-Cretaceous boundary.

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