Nature of the archean midcrust in the core of the Vredefort dome, Central Kaapvaal Craton, South Africa 1

Details Nature of the archean midcrust in the core of the Vredefort dome, Central Kaapvaal Craton, South Africa 1 Nature of the archean midcrust in the core of the Vredefort dome, Central Kaapvaal Craton, South Africa 1

Feb 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004gecoa..68..623l&link_type=abstract

Geochimica et Cosmochimica Acta, vol. 68, Issue 3, pp.623-642

Computer Science

11

Scientific paper

Extreme uplift associated with the formation of the 2.02 Ga Vredefort dome has exposed a substantial cross section through the crystalline early Archean basement complex rocks of the Kaapvaal craton. The rocks comprise polydeformed high-grade tonalite-trondhjemite-granodiorite (TTG) gneisses, migmatites and late-tectonic intrusive granitoids that straddle the upper amphibolite-to granulite-facies transition. Field, petrographic and geochemical data indicate that compositional heterogeneity occurs on a local scale and reflects the migmatitic character of the rocks rather than crustal-scale layering as has been previously proposed. No evidence has been found to support exposure of either a melt-depleted, refractory, lower crust or an upper crustal batholithic granite layer; however, the immense volume of granitic leucosome in the rocks suggests that the exposed section represents an intermediate level between these two zones. Granitic leucosomes in the upper amphibolite-facies migmatites appear to be intrusive into the predominantly trondhjemitic host rocks, rather than of in situ derivation. Leucosome compositions in the granulite-facies migmatites are more variable, ranging from granitic and charnockitic to enderbitic, probably reflecting at least some local derivation. Leucosomes and small granitoid bodies show local-scale geochemical variation that can be explained in terms of variable amounts of melt segregation and migration, and fractionation of minerals such as K-feldspar within the melts.

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