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Titre du document / Document title

The geology of the Vredefort dome :   ( explanation of sheets 2627CA, CB, CD, DA, DC, 2727AA, AB, BA - Scale 1 : 50000 )

Auteur(s) / Author(s)

Bisschoff A. A. ; Mayer J. J. (Collaborateur) ;

Affiliation(s) du ou des auteurs / Author(s) Affiliation(s)

Council for Geoscience (Editeur scientifique)

Résumé / Abstract

The Vredefort Structure is a ring structure which is elongated toward the southeast and is covered, in this direction, by Karoo-age sediments. Detailed mapping, carried out over the past decade, has indicated that its central core comprises Archaean gneiss and granulite (Inlandsee Gneiss), surrounded by a younger, more homogeneous granite and gneiss (Parys Granite). These rock types are separated by a zone of high-grade metamorphic rocks (the Steynskraal Metamorphic Suite) comprising migmatite, aluminous gneisses, granulite and charnockite of the granulite facies. Two large bodies of greenstone (Greenlands Formation) occur within the Parys Granite. The core of granite-gneiss is enveloped by a collar of sediments and lavas which progressively becomes younger towards the outer perimeters of the ring and ranges from Archaean to Early Proterozoic in age. They mostly dip steeply and are overturned in places. Basic lavas of the Dominion Group occur at the base of the collar, and are overlain by quartzite, shale, conglomerate and subordinate lava of the Witwatersrand Supergroup. Although lithostratigraphic terminology has not been finalised for the Witwatersrand succession in the Vredefort area, it is nevertheless possible to correlate successions of this area with those of the Central Rand and Klerksdorp areas down to the level of subgroups. The West Rand Group can accordingly be subdivided into the Hospital Hill, Govemment and Jeppestown Subgroups, each containing a number of characteristic subdivisions. The Central Rand Group comprises a number of quartzitic units with conglomeratic layers, and can be subdivided into the Johannesburg and Turffontein Subgroups. The latter Subgroups are separated by a formation of shaley character which could possibly be equated with the Booysens Shale Formation of the Central Rand. The Ventersdorp Supergroup, which is up to 3 600 m thick, is mainly represented by lavas of the Klipriviersberg Group. A ring synclinorium, consisting principally of rocks of the Transvaal Supergroup, follows the northern perimeter of the dome. The basal Black Reef Formation of the Transvaal Supergroup is between 10 and 20 m thick and is overlain by dolomite of the Malmani Subgroup. Hereupon follows the Pretoria Group, separated from the dolomite by a regional unconformity and subdivided into eight formations ranging from the Rooihoogte Formation to the Magaliesberg quartzite. The succession is intruded by a large number of diabase sills. Both the core and collar rocks are intruded by a variety of ultrabasic to alkali rocks. Dykes and sills of epidiorite, which are genetically linked to the Ventersdorp lavas, are particularly abundant in the pelitic units of the West Rand Group and also occur in the Parys Granite. Diabase and other tholeiitic basic rocks form, apart from dykes, also sills totalling a thickness up to 800 m. This group, which probably has a Bushveld age, includes the Losberg Complex. Dioritic and alkali plutons occur in fault zones but are, themselves, not displaced by the faulting.

Source / Source

1999  [Note(s) : IV, 49 p., ] (bibl.: 2 p.1/2) ISBN 1-875061-60-6 ;  Illustration : Illustration ;

Langue / Language

Anglais

Editeur / Publisher

Geological Survey of South Africa, Pretoria, AFRIQUE DU SUD  (1999) (Monographie)

Mots-clés anglais / English Keywords

Vredefort Dome

;

impact craters

;

meteor craters

;

gneisses

;

granites

;

stratigraphy

;

provenance

;

models

;

sedimentology

;

hornfels

;

epidiorite

;

diorites

;

intrusions

;

aplite

;

alkali granites

;

granophyre

;

metamorphism

;

pseudotachylite

;

shatter cones

;

mineralization

;

Orange Free State South Africa

;

South Africa

;

Southern Africa

;

Africa

;

metamorphic rocks

;

plutonic rocks

;

igneous rocks

;

metagabbro

;

metaplutonic rocks

;

metaigneous rocks

;

mylonites

;

Mots-clés français / French Keywords

Dôme Vredefort

;

Cratère impact

;

Cratère météoritique

;

Gneiss

;

Granite

;

Stratigraphie

;

Origine

;

Modèle

;

Sédimentologie

;

Cornéenne

;

Epidiorite

;

Diorite

;

Intrusion

;

Aplite

;

Granite alcalin

;

Granophyre

;

Métamorphisme

;

Pseudotachylite

;

Shatter cone

;

Minéralisation

;

Etat Orange

;

République Sud Africaine

;

Afrique du Sud

;

Afrique

;

Roche métamorphique

;

Roche plutonique

;

Roche ignée

;

Métagabbro

;

Roche métaplutonique

;

Roche métaignée

;

Mylonite

;

Mots-clés espagnols / Spanish Keywords

Domo Vredefort

;

Gneis

;

Granito

;

Estratigrafía

;

Origen

;

Modelo

;

Sedimentología

;

Corneana

;

Diorita

;

Intrusión

;

Aplita

;

Granito alcalino

;

Metamorfismo

;

Mineralización

;

Estado Orange

;

República de Sudáfrica

;

África Sur

;

Africa

;

Roca metamórfica

;

Roca granuda

;

Roca ignea

;

Metagabro

;

Roca metaplutónica

;

Roca metaígnea

;

Milonita

;

Localisation / Location

INIST-CNRS, Cote INIST : L 27284

Nº notice refdoc (ud2m) : 110775

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