Uranium irradiation history of carbonado diamond; implications for Paleoarchean oxidation in the São Francisco craton

Charles W. Magee, Guilherme Teles, Edward P. Vicenzi, Wayne Taylor, Peter Heaney

Research output: Contribution to journalArticle

4 Scopus citations

Abstract

Carbonado is a porous polycrystalline diamond rock found in central African and Brazilian placer deposits. It contains unsupported radiogenic isotopes of He, Ne, Kr, Xe, and Pb. Here we show that these, and the radiation-related defects introduced to the diamond structure, are a result of uranium precipitation, with no isotopic or spectroscopic evidence of Th enrichment. The daughter products are unsupported due to Proterozoic U remobilization. Combining existing carbonado Pb isotope data with recent studies of the geochronology of the tectonic evolution of the São Francisco craton (eastern South America) reveals that the most likely scenario is Paleoarchean uranium enrichment of carbonado, followed by Mesoproterozoic uranium dissolution. Under all possible scenarios, the carbonado radiation damage history requires U mobilization in the Mesoarchean or late Paleoarchean. This is consistent with recent studies of South Africa and India Mesoarchean paleosols, which also show evidence for local oxygen activity greater than that of the Archean atmosphere and ocean. While those studies rely on whole-rock trace element and transition metal stable isotope measurements, this combination of crystallographic defects, sedimentary geochronology, and radiogenic isotopes supports the same conclusions of nonmarine, near-surface Archean oxygen enhancement.

Original languageEnglish (US)
Pages (from-to)527-530
Number of pages4
JournalGeology
Volume44
Issue number7
DOIs
StatePublished - Jan 1 2016

All Science Journal Classification (ASJC) codes

  • Geology

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