Clastic sedimentation in a late Archaean accretionary terrain, Midlands greenstone belt, Zimbabwe

Late Archaean (∼2.68Ga) clastic sedimentary rocks of the Shamvaian Group form a shear zone-bounded lithotectonic unit in the Midlands greenstone belt (MGB) of Zimbabwe. The sedimentary rocks are wedged in between mid-Archaean granitoid gneisses and late Archaean mafic and bimodal volcanic rocks. The ≥2000-m thick sedimentary sequence consists of marine turbidite deposits overlain by high-energy shelf sandstone, fluvial braid-plain pebbly sandstone and alluvial fan conglomerate. Deposition took place in a northward-deepening basin with fluvial systems draining a source dominated by granitoid gneiss and banded chert. Basin formation was associated with a west-directed thrusting event, and the basin fill was incorporated into the thrust stack soon after deposition. The Shamvaian Group is similar to modern foreland and forearc successions and possibly accumulated during collision of a continental fragment with an island arc-like complex.