ABSTRACT
The Belingwe Greenstone Belt, with its excellent stratigraphic preservation, unconformities, komatiites and stromatolites, provides information on the structural, sedimentological, volcanological and palaeontological evolution of some Archaean rock suites. Nevertheless a number of geological problems remain unresolved.
The basement to the belt includes an ancient granitoid and gneiss terrain, of uncertain heritage prior to 3500 Ma and granitoid and gneissic rocks formed about 2900 Ma. On this was laid down the Hokonui succession, which may represent a single large andesitic volcano. Above and to the side of the Hokonui succession, subsidence allowed deposition of the alternating suite of komatiitic volcanic rocks and ironstones of the Bend Formation. This episode was terminated by marginal uplift and deposition of the conglomerates and felsic volcanics of the Koodoovale Formation. Possibly at the same time, the Brooklands Formation was deposited 60 km or more to the east in an actively faulted graben.
The Ngezi Group was probably formed in a later extensional event, in which initial sedimentation was followed by komatiitic volcanism (briefly) and then a substantial period of basaltic volcanism. Rift phase sedimentary deposits associated with mis event have not been identified. It is possible that some of the mafic volcanics were derived from a mid-crustal magma chamber similar to those preserved in me large ultramafic complexes of central Zimbabwe.
The structural evolution of the belt may have been consequent upon its initial rifting history. Offlapping strata may have been tightened into a syncline in which the preserved structural thickness is substantially increased by stacking of laterally juxtaposed depositional facies. Whether or not the site of the syncline reflects an initial basin within the craton-wide upper Bulawayan sequence remains controversial.
