The genesis of the quartz-sericite schists of the Toggekry Formation, Nondweni Greenstone Belt, South Africa.
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Date
2013
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Abstract
The aim of this study was to investigate the origin of sulphide-bearing quartz sericite-schists of
the Toggekry Formation in the Archaean Nondweni greenstone belt (NGB) in the SE Kaapvaal
craton, and to compare them with similar units in the Barberton greenstone belt (BGB).
Geochemical studies reveal that the quartz-sericite schists had a rhyolite protolith. These rocks
were subjected to two major deformation phases. D1 involved thrusting and stacking of the
greenstone stratigraphy while D2 formed the large syncline structure of the greenstone belt.
Within the study area, the F2 buckling mechanism seems to have been tangential longitudinal
strain. Peak metamorphism occurred after D2 at 3230 Ma when the Mvunyana granodiorite
intruded. The extensive alteration of the schists is interpreted as being partially due to the
deformation and metamorphism but mainly because of the position of the schists in the contact
metamorphic aureole of the Mvunyana granodiorite.
The tholeiitic and calc-alkaline signatures of both the mafic and felsic rocks of the Toggekry
Formation indicate that they formed in a back-arc setting. The enrichment in LREE relative to
HREE that the rocks display is characteristic of crustal contamination and/or subduction zone
magmas, enriched mantle source or small degrees of melting. The positive Pb anomalies and
negative Nb-Ta are characteristic of subduction zone processes and indicate crustal involvement
in the magma process. Epsilon Hf data suggests derivation either from a depleted mantle source
with contamination by older continental crust or from a depleted mantle at an earlier age
followed by re-melting.
The Toggekry Formation has an age of 3.54 Ga and is indistinguishable in age to the Theespruit
Complex of BGB. Both sequences are lithologically similar and interpreted as forming in backarc
settings. However significant geochemical differences indicate that they formed in coeval
but separate basins. Four models are proposed to account for this. The peak metamorphic event
at ca. 3.2 Ga in both areas is considered to reflect an accretionary event during the formation of the Kaapvaal craton.
Description
M. Sc. University of KwaZulu-Natal, Durban 2013.
Keywords
Quartz--KwaZulu-Natal--Nondweni., Quartz--Mpumalanga--Barbeton., Greenstone belts--KwaZulu-Natal--Nondweni., Greenstone belts--Mpumalanga--Barbeton., Theses--Geology.