Terra Nova, 24, 207–212, 2012


The subsurface structure of the Cape Fold Belt (CFB) that traverses southern Africa remains largely unknown because it lacks deep-penetrating, high-resolution geophysics. This hampers studies from local-scale exploration for important resources such as water, to continental-scale modelling, such as Gondwana reconstructions. Our Magnetotelluric (MT) soundings across the CFB provide a high-resolution crustal-scale electrical conductivity image. Inversion models of these data correlate well with surface geology, and resolve deep resistive roots of the CFB’s regional Palaeozoic quartzite ridges (Swartberg and Outeniqua Mountains) and thin tectonic wedges of Proterozoic rocks of higher resistivity (Kango and Kaaimans Inliers), separated by 2–3 km of Cretaceous sediments in asymmetric intermontaine basins. One of these basins, the Oudtshoorn Basin, is flanked by a listric normal fault rooted in an upper crustal detachment zone, and is underlain by a massive conductivity anomaly that is likely to be a major saline water reservoir.