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Comparison of Os and Cr Isotopic Methods for the Detection of Meteoritic Components in Impact Melt Rocks from the Morokweng and Vredefort Impact Structures, South AfricaThe verification of an extraterrestrial component in impact-derived melt rocks or breccias can be of diagnostic value to provide confirming evidence for an impact origin of a geological structure. Geochemical methods are used to determine the presence of the traces of such a component. In the absence of actual meteorite fragments, it is necessary to search for traces of meteoritic material that is mixed in with the target rocks in breccias and melt rocks. Meteoritic components have been identified for just over 40 impact structures (out of more than 160 known on Earth), which reflects also the detail in which these structures were studied. The identification of a meteoritic component can be achieved by determining the concentrations and interelement ratios of siderophile elements, especially the platinum group elements (PGE), which are several orders of magnitude more abundant in meteorites than in terrestrial upper crustal rocks. The usage of platinum group element abundances and ratios avoids some of the ambiguities that may result if only common siderophile elements (e.g., Cr, Co, Ni) are considered. However, problems may arise if the target rocks have high abundances of siderophile elements, or if the siderophile element concentrations in the impactites are very low. In such cases, the Os and Cr isotopic systems have recently been used for establishing the presence of a meteoritic component in a number of impact melt rocks and breccias. In the past it was attempted to use PGE data to determine the type or class of meteorite for the impactor, but these attempts were not always successful. It is difficult to decide between chondrite types based on PGE abundances, which has led to conflicting identifications for a number of impact structures. Clearly, the identification of a meteoritic component in impactites is not a trivial problem. In this study, we are using a combination of trace element (PGE) analyses and the results from both, Os and Cr isotopic studies, to illustrate the pros and cons of each method on two case studies, namely the Vredefort and Morokweng impact structures. Additional information is contained in the original extended abstract.
Document ID
20010007108
Document Type
Conference Paper
Authors
Koeberl, Christian
(Wien Univ. Austria)
Peucker-Ehrenbrink, Bernhard
(Woods Hole Oceanographic Inst. MA United States)
Reimold, Wolf Uwe
(Witwatersrand Univ. Johannesburg, South Africa)
Shukolyukov, Alex
(Scripps Institution of Oceanography San Diego, CA United States)
Lugmair, Guenter W.
(Scripps Institution of Oceanography San Diego, CA United States)
Date Acquired
August 20, 2013
Publication Date
January 1, 2000
Publication Information
Publication: Catastrophic Events and Mass Extinctions: Impacts and Beyond
Subject Category
Geophysics
Funding Number(s)
CONTRACT_GRANT: FFWF-Y58-GEO
CONTRACT_GRANT: NAG5-8172
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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IDRelationTitle20010007049Analytic PrimaryCatastrophic Events and Mass Extinctions: Impacts and Beyond
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