Portal de Periódicos da CAPES

Petrology and Geochemistry of Early Precambrian Graywackes from the Fig Tree Group, South Africa

1970; Geological Society of America; Volume: 81; Issue: 9 Linguagem: Inglês

10.1130/0016-7606(1970)81[2759

1943-2674

Kent C. Condie, JOHN E. MACKE, Thomas Reimer,

Geological formations and processes

Research Article| September 01, 1970 Petrology and Geochemistry of Early Precambrian Graywackes from the Fig Tree Group, South Africa KENT C CONDIE; KENT C CONDIE Department of Earth Sciences, Washington University, St. Louis, Missouri 63130 PRESENT ADDRESS (CONDIE): DEPARTMENT OF GEOSCIENCES, NEW MEXICO INSTITUTE OF MINING AND TECHNOLOGY, SOCORRO, NEW MEXICO 87801 Search for other works by this author on: GSW Google Scholar JOHN E MACKE; JOHN E MACKE Department of Earth Sciences, Washington University, St. Louis, Missouri 63130 Search for other works by this author on: GSW Google Scholar THOMAS O REIMER THOMAS O REIMER Department of Geology, University of Witwatersrand, Johannesburg, South Africa Search for other works by this author on: GSW Google Scholar GSA Bulletin (1970) 81 (9): 2759–2776. https://doi.org/10.1130/0016-7606(1970)81[2759:PAGOEP]2.0.CO;2 Article history received: 29 Dec 1969 rev-recd: 30 Mar 1970 first online: 02 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 KENT C CONDIE, JOHN E MACKE, THOMAS O REIMER; Petrology and Geochemistry of Early Precambrian Graywackes from the Fig Tree Group, South Africa. GSA Bulletin 1970;; 81 (9): 2759–2776. doi: https://doi.org/10.1130/0016-7606(1970)81[2759:PAGOEP]2.0.CO;2 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 SocietyGSA Bulletin Search Advanced Search Abstract Graywackes of the Fig Tree Group in South Africa were derived from a diverse source area composed principally of chert, volcanics, granitic-metamorphic rocks, and some ultramafics. Chert and quarts pseudomorphs after shard-like fragments and well-formed plagioclase and K-feldspar crystals in some graywackes indicate that some detritus was derived from contemporary volcanism. Immature textures indicate mild source-area weathering and rapid erosion, deposition, and burial. An unusually large amount of dolomite in the graywackes was probably deposited by carbonate-rich pore fluids during diagenesis. A relative Sr depletion (compared to K, Rb, Ca, and Ba) in graywackes of the lower Fig Tree Group (Sheba Formation) is interpreted in terms of an abundance of Sr-depleted igneous rocks in their source area. Large amounts of Ni in all Fig Tree graywackes and shales appear to have been derived from ultramafic source rocks.A progressive stratigraphic increase in granitic components in the graywackes suggests progressive unroofing of a granitic metamorphic terrane which was initially covered by a thick sequence of Onverwacht or Onverwacht-like volcanic rocks. This source appears to have been located in central Swaziland. The relatively abundant granitic detritus in the graywackes indirectly records one or more pre-Fig Tree (3.4-4.0 b.y.) granite-forming events in southern Africa. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.