CHERTS OF THE BARBERTON GREENSTONE BELT, SOUTH AFRICA: PETROLOGY AND TRACE-ELEMENT GEOCHEMISTRY OF 3.5 TO 3.3 GA OLD SILICIFIED VOLCANICLASTIC SEDIMENTS

Abstract

Research Article| December 01, 2013 CHERTS OF THE BARBERTON GREENSTONE BELT, SOUTH AFRICA: PETROLOGY AND TRACE-ELEMENT GEOCHEMISTRY OF 3.5 TO 3.3 GA OLD SILICIFIED VOLCANICLASTIC SEDIMENTS A. HOFMANN; A. HOFMANN Department of Geology, University of Johannesburg, P.O. Box 524, Auckland Park 2006, South Africa, e-mail: ahofmann@uj.ac.za Search for other works by this author on: GSW Google Scholar R. BOLHAR; R. BOLHAR Department of Geology, University of Johannesburg, P.O. Box 524, Auckland Park 2006, South Africa School of Earth Sciences, University of Queensland, Brisbane, Qld 4072, Australia, e-mail: rbolhar71@gmail.com Search for other works by this author on: GSW Google Scholar B. ORBERGER; B. ORBERGER ERAMET, 1 Avenue Albert Einstein, 78190 Trappes, France, Université Paris Sud XI, UMR IDES 8148, Département des Sciences de la Terre, Bât 504-509, 91405 Orsay Cedex, France, e-mail: beate.orberger@erametgroup.com Search for other works by this author on: GSW Google Scholar F. FOUCHER F. FOUCHER Centre de Biophysique Moléculaire, CNRS, Rue Charles Sadron, 45071 Orléans, France, e-mail: frederic.foucher@cnrs-orleans.fr Search for other works by this author on: GSW Google Scholar South African Journal of Geology (2013) 116 (2): 297–322. https://doi.org/10.2113/gssajg.116.2.297 Article history first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation A. HOFMANN, R. BOLHAR, B. ORBERGER, F. FOUCHER; CHERTS OF THE BARBERTON GREENSTONE BELT, SOUTH AFRICA: PETROLOGY AND TRACE-ELEMENT GEOCHEMISTRY OF 3.5 TO 3.3 GA OLD SILICIFIED VOLCANICLASTIC SEDIMENTS. South African Journal of Geology 2013;; 116 (2): 297–322. doi: https://doi.org/10.2113/gssajg.116.2.297 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietySouth African Journal of Geology Search Advanced Search Abstract A suite of green and carbonaceous black chert interbedded with submarine volcanic rocks from several stratigraphic levels of the Onverwacht Group of the Barberton greenstone belt, from the top of the ~3.48 Ga Komati Formation to the base of the ~3.26 Ga Fig Tree Group have been investigated petrologically and geochemically. Provenance analysis was undertaken using immobile trace element ratios in comparison with potential source rocks from the Barberton granitoid-greenstone terrain. Raman spectroscopy was used to better characterise carbonaceous matter in different chert varieties. Green cherts consist predominantly of silicified mafic to ultramafic volcaniclastic material. Black cherts contain volcaniclastic and/or epiclastic material of ultramafic to felsic composition, admixed with carbonaceous matter. In several cases, the clastic sediment is compositionally distinct to the volcanic substrate, suggesting that it represents volcanic material of relatively distal sources. Soon after settling out of the water column, lithification due to silicification took place. It gave rise to excellent textural preservation, but strongly modified the mineralogical and chemical composition of the seafloor sediments. Zircon, Cr-spinel and rare phosphate minerals are the only primary minerals remaining, while clastic grains have been largely replaced by a fine intergrowth of microquartz, Ti-oxide and K-bearing mica. Chemical changes are similar to those reported previously for silicification of volcanic rocks from the Barberton belt and are consistent with low-temperature hydrothermal processes common to the Palaeoarchaean seafloor environment. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.