Emplacement features of Archaean TTG plutons along the southern margin of the Barberton greenstone belt, South Africa
Kisters, A.F.M.; Anhaeusser, C.R.
Precambrian Research 75(1-2): 1-15
The Barberton greenstone belt in South Africa and its surrounding granitoid terrane represents one of the type localities for Archean granite-greenstone tectonics. Contact relationships between early Archean granitoids and greenstone sequences along the southern margin of the greenstone belt illustrate multiple, simultaneously operating emplacement mechanisms for the plutons. These emplacement mechanisms, which can be identified in individual plutons comprise ductile wall-rock deformation, stoping, assimilation, and the intrusion of ring dykes. The interaction between these various mechanisms is interpreted to be responsible for the complex and highly variable discordant and concordant contact relationships observed in the granite-greenstone terrane as well as the deformation observed within wall rocks and country-rock xenoliths. The absence of regionally consistent fabrics within the plutons suggests considerable competence contrasts between the tonalitic-trondhjemitic plutons and, in many cases, the hydrated greenstone cover-sequence during later subhorizontal crustal shortening which occurred parallel to the greenstone-granitoid interface. This competence contrast is interpreted to have resulted in the accentuation of cuspate-lobate folds along the granitoid-greenstone interface, being partly responsible for the typical arcuate, dome-and-keel geometry of the Barberton greenstone belt.