Abstract

The structure and subsurface configuration of the Masvingo Greenstone Belt (MGB) in the Zimbabwe Craton (ZC), were investigated using aeromagnetic and gravity data. Gravity data from 158 new and 202 old gravity stations were combined to produce a Bouguer gravity map covering the greenstone belt and surrounding granites. The greenstone belt and ultramafic complexes are characterised by Bouguer gravity highs, whereas the granitic terrain are lows, with the lowest values over the post-volcanic plutons. Gravity modelling, constrained by surface geology and density measurements, was carried out on a profile crossing the greenstone belt. The modelling results indicate a depth extent of around 6 km for the dense greenstone belt with a thickness of about 8.5 km for the adjacent younger granite plutons, which are significantly less dense. Granite-greenstone contacts along the profile are near-vertical.

Magnetic maps compiled from the Zimbabwe Geological Survey national aeromagnetic data set show the bulk of the greenstone belt to have low magnetic anomaly values, but with high magnetic anomaly values along its northern and western margins over ultramafic units and banded iron formations. The younger granites generally have higher magnetic anomaly values compared to both the greenstone belt and the older gneisses. In particular, a pronounced east-northeast-trending broad magnetic high is observed over the Charumbira pluton, and its edges mark the boundaries with the greenstone belt to the north, and the Limpopo belt to the south; with the latter characterised by low magnetic values. Several linear, small amplitude magnetic lows, which are mostly due to faults, trend northwest to southeast and north to south, with some revealing an apparent dextral movement. Derivative maps for both gravity and magnetic data bring out some of the linear features and the edges of the greenstone belt and granite plutons. Shallow and deep depth slices of the magnetic field allow separation of high and low frequency anomalies; such as the east-northeast-trending Limpopo dyke swarm of Karoo age.

The information obtained from modelling, derivative maps and depth slicing suggest a trough-shaped configuration for the MGB, which is consistent with other known greenstone belts on the ZC and elsewhere. This information is consistent with an intracratonic, extensional rift environment for emplacement of the greenstone belt.

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