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Euler deconvolution and spectral analysis of regional aeromagnetic data from the south-central Zimbabwe craton: tectonic implications

R.T. Ranganai

Abstract


Existing regional aeromagnetic data from the south-central Zimbabwe craton has been analysed using 3D Euler deconvolution and spectral analysis to obtain quantitative information on the geological units and structures for depth constraints on the geotectonic interpretation of the region. The Euler solution maps confirm and extend the structural pattern previously identified using shaded relief imaging and derivative techniques: ENE, NNE, NNW, NW and WNW; thus confirming the geological significance of the qualitative interpretation. In places, Euler solutions also show additional patterns typical of sill-edges, thus mapping previously unrecognised mafic/ ultramafic intrusions. Most structures identified are predominantly of shallow origin, with Euler depths solutions 1.0 km, and cut across the greenstone belts. A number of isolated deep Euler solutions are associated with ultramafic complexes, the Great Dyke and the Umvimeeela dyke; and these points could represent the original magma chambers and/or feeder points for these units. A linear cluster of solutions with depths around 2.0 km marks the Zimbabwe craton-Limpopo Belt boundary remarkably well. Spectral analysis results suggest the magnetic basement at about 8 km depth, and this probably corresponds to a crustal boundary deduced from gravity and seismic data to occur at 7-9 km depth.The geostructural framework of the area is compatible with the postulated late Archaean collision involving the Zimbabwe and Kaapvaal cratons and the Limpopo Belt, and later crustal extension during the break-up of Gondwana. The geological-tectonic correlation suggests that the interpreted regional trends are mainly 2.6 Ga and younger, and relate to tectonic events including the reactivation of the Limpopo Belt at 2.0 Ga and the major regional igneous/ dyking events at 1.8-2.0 Ga (Mashonaland), 1.1 Ga (Umkondo) and 180 Ma (Karoo). The greenstone belts were an integral part of the lithosphere before much of the upper crustal (brittle) deformation occurred.

Keywords: Aeromagnetic data, Euler deconvolution, Spectral analysis, Tectonic interpretation, Zimbabwe craton




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