Search for a meteoritic component in drill cores from the Bosumtwi impact structure, Ghana: Platinum group element contents and osmium isotopic characteristics
Meteoritics and Planetary Science
School of Earth Ocean and Planetary Sciences, Cardiff University, Park Place, Cardiff CF10 3YE, United Kingdom; Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, 360 Woods Hole Road, Woods Hole, MA 02543-1541, United States; Impact Cratering Research Group, School of Geosciences, University of the Witwatersrand, Private Bag 3, Johannesburg 2050, South Africa; Department of Geological Sciences, University of Vienna, Althanstrasse 14, Vienna A-1090, Austria; Department of Mineralogy, Museum for Natural History, Humboldt University in Berlin, Invalidenstrasse 43, D-10115 Berlin, Germany
An attempt was made to detect a meteoritic component in both crater-fill (fallback) impact breccias and fallout suevites (outside the crater rim) at the Bosumtwi impact structure in Ghana. Thus far, the only clear indication for an extraterrestrial component related to this structure has been the discovery of a meteoritic signature in Ivory Coast tektites, which formed during the Bosumtwi impact event. Earlier work at Bosumtwi indicated unusually high levels of elements that are commonly used for the identification of meteoritic contamination (i.e., siderophile elements, including the platinum group elements [PGE]) in both target rocks and impact breccias from surface exposures around the crater structure, which does not allow unambiguous verification of an extraterrestrial signature. The present work, involving PGE abundance determinations and Os isotope measurements on drill core samples from inside and outside the crater rim, arrives at the same conclusion. Despite the potential of the Os isotope system to detect even small amounts of extraterrestrial contribution, the wide range in PGE concentrations and Os isotope composition observed in the target rocks makes the interpretation of unradiogenic, high-concentration samples as an impact signature ambiguous. © The Meteoritical Society, 2007. Printed in USA.