Tectonic evolution of the Bindura-Shamva greenstone belt (northern Zimbabwe): Progressive deformation around diapiric batholiths

Abstract

The Bindura-Shamva greenstone belt (northern Zimbabwe) and adjacent batholiths are regarded as one of the type areas for granite-greenstone tectonics. Structural observations and three-dimensional strain analyses have been used to propose a model for the tectonic evolution of this late Archaean greenstone belt. The data indicate that pluton emplacement triggered the deformation of the greenstone sequences and that the deformation history is single-phase progressive rather than polyphase. They do not, however, lead to an unambiguous interpretation of the emplacement mechanism. Structural features are best explained by a combination of pluton diapirism and ballooning plutonism. Criteria used as evidence for pluton-related deformation include the pattern of foliation and stretching lineation trajectories, the variation in strain type and strain intensity, fold types, sense of shear at the batholith-greenstone interface, metamorphic zoning and timing of porphyroblast growth. Specific structural and strain patterns within cleavage triple points, interdomal synclinoria (saddle culminations) and batholith margins demonstrate interference between strain fields developed around each batholith.