Download Folding, Thrusting and granitoids along the edge of the Kaapvaal

Folding, Thrusting and granitoids along the edge of the
Kaapvaal Craton
J. van Bever Donker1, R. Bailie2, S. Stakou3, E. Saffou4, T. Shunqukela5
1. Department of Earth Sciences, University of the Western Cape, South Africa, [email protected]
2 Department of Earth Sciences, University of the Western Cape, South Africa, [email protected]
3 Department of Earth Sciences, University of the Western Cape, South Africa,2832211 @uwc.ac.za
4 Department of Earth Sciences, University of the Western Cape, South Africa, [email protected]
5 Department of Earth Sciences, University of the Western Cape, South Africa, [email protected]
ABSTRACT
On the official Upington Sheet as edited by Moen, the Neusspruit lineament is an unimportant small regional
phenomenon. The geology of the area is placed in the Korannaland Group of the Kakamas Terrane and shows a
series of metasedimentary rocks, with amphibole- biotite gneiss at the base, followed by a calcisilicate rich fine
grained quartzite and capped by a coarse cross-bedded feldspathic quartzite.
Our investigations have revealed that the area is intensely deformed as a result of NW-SE directed stresses.
Deformation was intense in a transpressive environment producing a sheath fold of exceptional magnitude (30 km
length) in cross bedded quartzites. The geotectonic environment that produced the rocks and the structures is likely
governed by the accretionary processes during which the Kakamas Terrane was added to the Kaapvaal Craton as
the fore-arc basin to the subduction zone as expressed by the Areachap Group.
Initial geochemical results confirm this scenario in that the overall provenance of the metasediments of the
Korannaland Group in the Kakamas Terrane was derived from a relatively unfractionated, mafic provenance. The
amphibolites were extruded as mafic lava flows in an active continental island arc setting likely related to the
Areachap Group volcanic arc to the east. The calc-silicates and the feldspathic quartzites were deposited in a
continental island arc to active continental margin setting suggesting that the Kakamas Terrane represents the forearc wedge or trench sediments to the Areachap Group volcanic arc to the east (confirmed by a palaeocurrent
direction, although influenced by deformational events, predominantly from the east). There were outpourings of
mafic lavas with variable degrees of detrital input (the amphibolites) with the calc-silicates deposited on an
unstable continental margin.
The Friersdale charnockite has an age of 1087 Ma and intruded post-kinematically. It was derived from a depleted
mantle source, was water-saturated, and crystallised in the mid- to upper continental crust. This granite is relatively
unfractionated and was contaminated slightly by re-melting of older crust. It has a within plate granite tectonic
setting and intruded after the tectonic events which took place between the Namaqua Sector and the Kaapvaal
Craton.
KEYWORDS: Korannaland Group, Sheath folding, Thrusting, Geochemistry, Fore Arc Basin
Inkaba yeAfrica : 9th Annual Workshop, Germany - 2012