The Broodkop shear zone, southeast Vredefort dome (South Africa): a Dominion-related extensional feature?

Abstract

Research Article| September 01, 2006 The Broodkop shear zone, southeast Vredefort dome (South Africa): a Dominion-related extensional feature? Cristiano Lana; Cristiano Lana Impact Cratering Research Group, School of Geosciences, University of the Witwatersrand, Private Bag 3, P.O. Wits 2050, Johannesburg, South Africa, Impacts and Astromaterials Research Centre, Imperial College London, Royal School of Mines, South Kensington Campus, United Kingdom, SW7 2AZ, e-mail: c.lana@imperial.ac.uk Search for other works by this author on: GSW Google Scholar Roger L. Gibson; Roger L. Gibson Impact Cratering Research Group, School of Geosciences, University of the Witwatersrand, Private Bag 3, P.O. Wits 2050, Johannesburg, South Africa, e-mail: gibsonr@geosciences.wits.ac.za Search for other works by this author on: GSW Google Scholar Wolf Uwe Reimold Wolf Uwe Reimold Impact Cratering Research Group, School of Geosciences, University of the Witwatersrand, Private Bag 3, P.O. Wits 2050, Johannesburg, South Africa Museum für Naturkunde, Humboldt University, Invalidenstrasse 43, 10115 Berlin, e-mail: uwe.reimold@museum.hu-berlin.de Search for other works by this author on: GSW Google Scholar Author and Article Information Cristiano Lana Impact Cratering Research Group, School of Geosciences, University of the Witwatersrand, Private Bag 3, P.O. Wits 2050, Johannesburg, South Africa, Impacts and Astromaterials Research Centre, Imperial College London, Royal School of Mines, South Kensington Campus, United Kingdom, SW7 2AZ, e-mail: c.lana@imperial.ac.uk Roger L. Gibson Impact Cratering Research Group, School of Geosciences, University of the Witwatersrand, Private Bag 3, P.O. Wits 2050, Johannesburg, South Africa, e-mail: gibsonr@geosciences.wits.ac.za Wolf Uwe Reimold Impact Cratering Research Group, School of Geosciences, University of the Witwatersrand, Private Bag 3, P.O. Wits 2050, Johannesburg, South Africa Museum für Naturkunde, Humboldt University, Invalidenstrasse 43, 10115 Berlin, e-mail: uwe.reimold@museum.hu-berlin.de Publisher: Geological Society of South Africa First Online: 09 Mar 2017 Online ISSN: 1996-8590 Print ISSN: 1012-0750 © 2006 Geological Society of South Africa South African Journal of Geology (2006) 109 (3): 265–278. https://doi.org/10.2113/gssajg.109.3.265 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 Cristiano Lana, Roger L. Gibson, Wolf Uwe Reimold; The Broodkop shear zone, southeast Vredefort dome (South Africa): a Dominion-related extensional feature?. South African Journal of Geology 2006;; 109 (3): 265–278. doi: https://doi.org/10.2113/gssajg.109.3.265 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 The Broodkop shear zone is an approximately 1 km-wide, vertical, northeasterly-trending, mylonitic shear zone that separates upper amphibolite- to granulite-facies gneisses (≥670°C, 4.5 to 5.5 kbar) from mid-greenschist-facies (~400°C) greenstones in the southeastern part of the Vredefort dome. The mylonitic fabric transposes 3.09 to 3.08 Ga peak-metamorphic migmatitic structures but shows progressive overprinting of shear-related amphibolite-facies assemblages by greenschist-facies assemblages; indicating initiation of deformation close to the metamorphic peak and continued shearing during cooling. Shear-sense indicators are consistent with southeastern-side-up dip-slip movement. Removal of Late Archaean and Proterozoic rotation effects, particularly those associated with formation of the Vredefort dome, suggests that the shear zone formed as a shallowly northwesterly-dipping extensional feature associated with exhumation of the mid-crustal amphibolite-to-granulite-facies footwall rocks and transport of the greenschist-facies hanging wall rocks to the northwest. Several kilometres of throw along the shear zone is suggested by the juxtaposition of rocks with markedly different metamorphic grades. Assuming an initial shallow dip for the shear zone, this suggests in excess of 10 km of dip-slip movement, making the Broodkop shear zone a crustal-scale feature. The timing and geometry of the shear zone suggest that it may represent a mid-crustal manifestation of the rifting event that led to the deposition of bimodal volcanics and associated sediments of the 3074 ± 6 Ma Dominion Group. The Broodkop shear zone provides an appropriate mechanism to explain how these volcanics could be deposited unconformably on mid-crustal gneisses within only a few million years of the high-grade metamorphism. It provides a link between the final major pulse of greenstone-TTG formation in the core of the Vredefort dome and the initiation of a series of large sedimentary and volcanic basins that dominated the Late Archaean history of the Kaapvaal craton. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.