Electrical Conductivity and Potential Field Data in Namibia

Within the framework of an amphibian experiment in 2011, magnetotelluric (MT) data were recorded at 167 land stations along a 140 km wide swath and 30 ocean bottom sites along a cost-parallel and a cost-perpendicular profile (SAMPLE proposals RI 1127/9-1). Visual inspection as well as dimensionality analysis of the onshore MT data indicates complex three-dimensional (3D) subsurface structures across the Kaoko Belt. To construct a preliminary electrical conductivity section, we applied two-dimensional (2D) inversion to a sub-set of the data. The 2D inversion models show good correlation with surface geology and tectonic units. The Etendeka Flood Basalts appear as a deep reaching zones of high resistivity, while faulted and anticlinal structures are highly conductive. Some of the features are quite unexpected, however, such as zones of high conductivity beneath the Congo Craton. The onset of the Congo Craton appears to be well resolved in gravity data while some of the observed zones of high conductivity coincide spatially with magnetic anomalies.

We therefore suggest using gravity and aeromagnetic data which is available from the Geological Survey of Namibia and from NAMCOR to obtain 2D and 3D potential field models. With this proposal, we inted to (i) model aeromagnetic and gravity data in the region of the MT swath using IGMAS, (ii) constrain 2D and 3D MT models using the obtained potential field models, (iii) use seismic and seismological results obtained within SAMPLE (phase II) as additional constraints, (iv) elaborate empirical relations between electrical conductivity and magnetization locally (based on fitting probability density functions) and (v) derive a consistent geological interpretation of the Kaoko Belt, its interaction with the Walvis Ridge and the transition to the Congo Craton.

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