Geochemistry across an exposed section of Archaean crust at Vredefort, South Africa; with implications for mid-crustal discontinuities

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Authors:Hart, Rodger J.; Andreoli, Marco A. G.; Tredoux, Marian; De Wit, Maarten J.
Author Affiliations:Primary:
Univ. Witwatersrand, Schonland Res. Cent., Johannesburg, South Africa
At. Energy Corp. S. Afr., South Africa
Univ. Cape Town, South Africa
Volume Title:Chemical Geology
Source:Chemical Geology, 82(1-2), p.21-50. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0009-2541
Publication Date:1990
Note:In English. 69 refs.; illus. incl. 7 tables, geol. sketch map
Summary:The central region of the Vredefort structure consists of a semi- circular multi-layered sequence of crystalline rocks which are nearly vertical in attitude, and increasing in metamorphic grade towards the core of the structure. Together with overlying Precambrian strata, this sequence provides a cross-section through almost the entire crustal section of the Kaapvaal craton (36 km). The upper part of the Vredefort crystalline crust consists of a 3000 m.y. sequence of differentiated felsic rocks of amphibolite facies. The lower crust consists of a complex and heterogenous high-grade metamorphic terrain of charnockites, granulites (mafic and felsic) and supracrustal rocks. The upper crust is separated from the lower by the Vredefort discontinuity, a brittle-ductile shear zone characterized by a high concentration of pseudotachylite and brecciated rock. Petrographic, chemical and isotopic evidence suggest that the upper and lower crust have undergone very different styles of evolution. This is indicative of different geological environments prior to their present juxtaposition. The present authors speculate that the upper and lower parts of the Vredefort crystalline crust were juxtaposed during intracratonic thrusting approx 2800 m.y. ago, and that the entire 36 km section of crust, including the Vredefort discontinuity, were rotated and uplifted into their present vertical position during the 2000 m.y. Vredefort catastrophe. [Authors' abstract] [P.Br.]
Subjects:Archean; Continental crust; Cratons; Crust; Cryptoexplosion features; Discontinuities; Domes; Faults; Geochemical profiles; Geochemistry; Major elements; Metamorphic rocks; Precambrian; Shear zones; Thrust faults; Trace elements; Africa; Free State South Africa; Kaapvaal Craton; South Africa; Southern Africa; Vredefort Dome; Orange Free State South Africa
Coordinates:S273000 S263000 E0280000 E0270000
Abstract Numbers:90M/4437
Record ID:1990048318
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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