The 3.5 Ga Komati Formation, Barberton Greenstone Belt, South Africa, Part I: New maps and magmatic architecture

Research Article| March 01, 2000 The 3.5 Ga Komati Formation, Barberton Greenstone Belt, South Africa, Part I: New maps and magmatic architecture J.C. Dann J.C. Dann Department of Geological Sciences, University of Cape Town, Rondebosch, 7700 Republic of South Africa, E-mail: jcdann@mit.edu *present address: Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, 02139, U.S.A. Search for other works by this author on: GSW Google Scholar Author and Article Information J.C. Dann *present address: Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, 02139, U.S.A. Department of Geological Sciences, University of Cape Town, Rondebosch, 7700 Republic of South Africa, E-mail: jcdann@mit.edu Publisher: Geological Society of South Africa Accepted: 01 Mar 2000 First Online: 07 Mar 2017 Online ISSN: 1996-8590 Print ISSN: 1012-0750 © 2000 Geological Society of South Africa South African Journal of Geology (2000) 103 (1): 47–68. https://doi.org/10.2113/103.1.47 Article history Accepted: 01 Mar 2000 First Online: 07 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation J.C. Dann; The 3.5 Ga Komati Formation, Barberton Greenstone Belt, South Africa, Part I: New maps and magmatic architecture. South African Journal of Geology 2000;; 103 (1): 47–68. doi: https://doi.org/10.2113/103.1.47 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 '3.48 Ga Komati Formation, famous for its spinifex komatiites, was mapped (1:5000 scale) to provide an objective base for reconstructing the magmatic and tectonic architecture. All outcrops were drafted on digital orthophotographs using GIS software. The best outcrops were mapped to determine the textural zoning and shapes of chill-bound cooling units and to distinguish volcanic, intrusive, and tectonic contacts. The Komati and overlying Hooggenoeg Formations compose a 6-km-thick section of submarine lava flows and intrusions. The section is overlain by c. 3.45 Ga dacitic volcanic rocks, and the Komati Shear Zone marks the base. The Komati Formation is divided into upper and lower members. The Lower Komati, 1.3 km thick, consists of layers of olivine komatiite (48%) and komatiltic basalt (52%). The Upper Komati, 1.8 km thick, consists predominantly of pillow lavas of komatiitic basalt (84%). Komatiites of the Lower Komati consist of massive (6 1%), spinifex (37%), and vesicular (2%) cooling units. Massive units are interpreted to be undifferentiated sheet flows (50m thick by 11 km in extent). Spinifex komatiites are concentrated in five distinct horizons that generally overlie thicker massive sheets. Spinifex cooling units occur as sheet flows (8 m by >1 km) and thinner lenses that are analogous to pahoehoe flow lobes. Vesicular komatiite occurs as a sheet (~.11 m by >1.8 km) and a channel (55 m by <0.3 km) with 20 – 25% vesicles, locally interlayered in zones with olivine spinifex. Interlayered with pillows in the Upper Komati, sheet flows of komatiitic basalt (5–15 m thick) have pyroxene-spinifex zones. Similar textures occur in locally crosscutting sills in the Lower Komati. Dykes and sills of komatiite, kornatiitic basalt, diabase, tonalite, and wehrlite intruded the Komati Formation. Komatiitic dykes occur within cooling units and may be related to inflation of volcanic flows. Wehrlite dykes, compositionally similar to the komatiites, are younger intrusions, possibly related to an overlying volcanic sequence. Dykes and sills of komatiitic basalt may relate to volcanic rocks in the Upper Komati or Upper Hooggenoeg Formation. Volcanic flows occur at the structural base of the Komati Formation with no evidence for sheeted dykes. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.