Archaic spherule deposits from the metasedimentary rock sequences of the Barberton Greenstone Belt (BGB) in South Africa are among the oldest known records of meteorite impacts on Earth. Spherules in these deposits have been interpreted as melted impact ejecta particles and condensation products from the impact plume, or as impact ejecta that melted upon re-entry into the atmosphere. Extremely high iridium concentrations and the chromium isotope ratios in these deposits have shown that some samples from spherule deposits must consist exclusively of extraterrestrial material. At the Museum für Naturkunde, spherule layers from various drill cores (ICDP borehole BARB-5, Sabi Gold CT3 exploration borehole, Fairview Gold Mine exploration boreholes) were examined. A project on the ICDP BARB-5 borehole showed in which microphases this extraterrestrial component can be found. For the first time, heterogeneous sub- and micrometer-sized platinum group element (PGE) nuggets were located. Their origin is the subject of controversy: vapor plume condensates versus ejected ejecta melt droplets. The investigation of further drill cores should clarify whether the novel observations and results of the ICDP BARB-5 study are symptomatic of other (all?) spherule layers, e.g., with regard to the composition of PGE micronuggets and the occurrence of such nuggets in and between individual spherules. Furthermore, the drilled archaic rock sequences provide information about the frequency of impacts and the types of projectiles that collided with Earth during the early Archean and thus played a significant role in the planetary evolution of Earth and the solar system.
Methodology
High-resolution electron microscopy: FE-SEM/EDX, TEM, EBSD, and TKD; geochemistry of major and trace elements, including platinum group elements (PGE); Ru isotope studies
Partners
- Bruker Nano GmbH, Berlin
- Bundesanstalt für Materialforschung und –prüfung (BAM), Berlin
- Centre de Recherches Pétrographiques et Géochimiques, Université de Lorraine, Nancy, France
- Department für Lithosphärenforschung, Universität Wien, Austria
- Department of Geology, University of Johannesburg, South Africa
- Instituto de Geociencias, Federal University of Campinas, Brasil
- GeoSpectral Imaging, Johannesburg, South Africa
- GFZ Helmholtz-Zentrum für Geoforschung, Potsdam
- Institut für Geologie, Universität Münster
- Institut für Geologie und Mineralogie, Universität Köln
- Institut für Geowissenschaften, Universität Bonn
- Natural History Museum, London, Great Britain
- Naturhistorisches Museum Wien, Austria
- University of Brasilia, Brasil
Funding and duration
- DFG funding: 15.07.2013-15.07.2015
- EUROPLANET project funding: 09.11.-23.11.2016
Publications
- SALGE, T. and MOHR-WESTHEIDE, T. 2023.
Detection and Quantification of Extraterrestrial Platinum Group Element Alloy Micronuggets from Archean Impactite Deposits by Low-Voltage Scanning Electron Microscopy/Energy-Dispersive X-ray Spectrometry. Microscopy and Microanalysis 29(6). DOI:10.1093/micmic/ozad088 - OLIVEIRA, G.J.G. DE, REIMOLD, W.U., CROSTA, A.P., HAUSER, N., KOEBERL, C., MADER, D., SCHMITT, R.T. and MOHR-WESTHEIDE, T. 2021.
Terrestrial and extraterrestrial geochemical components of Early Archean impact spherule layers from Fairview Gold Mine, Northern Barberton Greenstone Belt, South Africa. Geological Society of America Special Paper 550 “Large Meteorite Impacts and Planetary Evolution VI” (edited by Reimold, W. U. and Koeberl, C.), Chapter 12, 297-332, DOI: 10.1130/2021.2550(12). - MOHR-WESTHEIDE, T., GRESHAKE, A., WIRTH, R. and REIMOLD, W. U. 2018.
Transmission Electron Microscopy of Impact-Generated Platinum-Group Element Alloys from Barberton Spherule Layers: New Clues to their Formation. Meteoritics and Planetary Science 53(7), 1516-1536. DOI: 10.1111/maps.13109. - HOEHNEL, D., REIMOLD, W.U., ALTENBERGER, U., HOFMANN, A., MOHR-WESTHEIDE, T., OEZDEMIR, S. and KOEBERL, C. 2017.
Petrographic and Micro-XRF Analysis of Multiple Archean Impact-Derived Spherule Layers in Drill Core CT3 from the northern Barberton Greenstone Belt (South Africa). Journal of African Earth Sciences 138 (2): 264-288. DOI: 10.1016/j.jafrearsci.2017.11.020. - OEZDEMIR, S., SCHULZ, T., KOEBERL, C., REIMOLD, W.U., MOHR-WESTHEIDE, T., HOEHNEL, D. and SCHMITT, R.T. 2017.
Early Archean Spherule Layers from the Barberton Greenstone Belt, South Africa: Mineralogy and Geochemistry of the Spherule Beds in the CT3 Drill Core. Meteoritics & Planetary Science 52:2586-2631. DOI:10.1111/maps.12998 - SCHULZ, T., KOEBERL, C., LUGUET, A., VAN ACKEN, D., MOHR-WESTHEIDE, T., OEZDEMIR, S. and REIMOLD, W.U. 2017.
New constraints on the Paleoarchean meteorite bombardment of the Earth - Geochemistry and Re-Os isotope signatures of spherule layers in the BARB5 ICDP drill core from the Barberton Greenstone Belt, South Africa. Geochimica et Cosmochimica Acta 211, 322-340, DOI: 10.1016/j.gca.2017.05.040. - FRITZ, J., ROALD, T., ASHWORTH, L., SCHMITT, R.T., HOFMANN, A., LUAIS, B., HARRIS, P.D., HOEHNEL, D., OZDEMIR, S., MOHR-WESTHEIDE, T. and KOEBERL, C. 2016.
Nondestructive spectroscopic and petrochemical investigations of Paleoarchean spherule layers from the ICDP drill core BARB5, Barberton Mountain Land, South Africa. Meteoritics and Planetary Science 51, 2441-2458. DOI: 10.1111/maps.12736. - MOHR-WESTHEIDE, T., REIMOLD, W. U., FRITZ, J., KOEBERL, C., SALGE, T., HOFMANN, A. and SCHMITT, R.T. 2015.
Discovery of extraterrestrial component carrier phases in Archean spherule layers: Implications for estimation of Archean bolide sizes. GEOLOGY, 43(4), 299-302. DOI: 10.1130/G36548.1.