Early Archean spherule layers from the Barberton Greenstone Belt, South Africa
- Author(s)
- Seda Oezdemir, Toni Schulz, Christian Koeberl, Wolf Uwe Reimold, Tanja Mohr-Westheide, Desiree Hoehnel, Ralf Thomas Schmitt
- Abstract
Little is known about the Hadean and the Archean impact record on Earth. In the CT3 drill core from the Fig Tree Group of the northern Barberton Greenstone Belt, 17 spherule layer intersections occur, which, provide an outstanding new opportunity to gain insights into meteorite bombardment of the early Earth. CT3 spherules, as primary features, mostly exhibit textural patterns similar to those of the other Barberton spherule layers, but locally mineralogical and chemical compositional differences are observed, likely as a result of various degrees of alteration. The observed mineralogy of the spherule layers is of secondary origin and comprises K-feldspar, phyllosilicates, carbonates, sulfides, and oxides, with the exception of secondary Ni-Cr spinel that is of primary origin. Our petrographic investigations suggest alteration by K-metasomatism, sericitization, silicification, and carbonatization. Siderophile element contents of bulk samples show significant enrichments in Ni (up to 2 wt%) and Ir (up to ~3 ppm), similar to previously studied Archean spherule layers. These values are indicative of the presence of a meteoritic component. On the other hand, lithophile and chalcophile element abundances indicate hydrothermal overprint on the CT3 samples; this may also have influenced the redistribution of the meteoritic component(s). Last, we group the CT3 spherule layers, which occur in three intervals (A, B, and C), according to their petrographic and geochemical features, which indicate evidence for at least three distinct impact events before tectonic overprint that affected the original deposits.
- Organisation(s)
- Department of Lithospheric Research
- External organisation(s)
- Naturhistorisches Museum Wien (NHM), Museum für Naturkunde Berlin - Leibniz-Institut für Evolutions- und Biodiversitätsforschung, Humboldt-Universität zu Berlin, Universidade de Brasília, Freie Universität Berlin (FU)
- Journal
- Meteoritics and Planetary Science
- Volume
- 52
- Pages
- 2586-2631
- No. of pages
- 46
- ISSN
- 1086-9379
- DOI
- https://doi.org/10.1111/maps.12998
- Publication date
- 12-2017
- Peer reviewed
- Yes
- Austrian Fields of Science 2012
- 105105 Geochemistry
- Keywords
- ASJC Scopus subject areas
- Geophysics, Space and Planetary Science
- Sustainable Development Goals
- SDG 15 - Life on Land
- Portal url
- https://ucrisportal.univie.ac.at/en/publications/c6a457f2-b329-4239-b1f9-a29c4fe1a627