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Book Chapter

Archean spherule layers in the Barberton greenstone belt, South Africa: A discussion of problems related to the impact interpretation

By
Axel Hofmann
Axel Hofmann
Impact Cratering Research Group, School of Geosciences, University of the Witwatersrand, Private Bag 3, 2050 Wits, Johannesburg, South Africa
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Wolf Uwe Reimold
Wolf Uwe Reimold
Impact Cratering Research Group, School of Geosciences, University of the Witwatersrand, Private Bag 3, 2050 Wits, Johannesburg, South Africa, and Museum für Naturkunde (Mineralogy), Humboldt University, Invalidenstrasse 43, 10115 Berlin, Germany
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Christian Koeberl
Christian Koeberl
Department of Geological Sciences, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria
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Published:
January 01, 2006

This review of the current knowledge of impact spherule layers in the Barberton greenstone belt, together with new petrographic, geochemical, and field data on a number of impact and volcanic spherical particle horizons, highlight a number of problems with the proposition of frequent and large meteorite impacts during mid-Archean times. Field data indicate that some of the four previously proposed impact spherule layers may be laterally correlative units that may have formed from the same impact event. Petrographic work reveals the presence of volcaniclastic particles associated with some spherule layers, while other layers not regarded as impact deposits contain clasts commonly observed in the spherule beds. Major and trace element compositions of spherule layers reflect the composition of the immediate host rocks. The existing platinum group element and chromium isotope data are difficult to reconcile with the current knowledge of the composition of meteoritic debris. A thorough discussion of these problems is necessary before meaningful estimates of Archean impact flux and bolide diameters should be attempted.

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Contents

GSA Special Papers

Processes on the Early Earth

Wolf Uwe Reimold
Wolf Uwe Reimold
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Roger L. Gibson
Roger L. Gibson
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Geological Society of America
Volume
405
ISBN print:
9780813724058
Publication date:
January 01, 2006

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