Constrained modelling of electromagnetic and potential field data to investigate the Walvis Ridge magmatism and its interaction with the Kaoko Mobile Belt, Namibia.

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Within the framework of an amphibian magnetotelluric experiment in 2011, the Walvis Ridge magmatism and its interaction with the Kaoko Mobile Belt in northern Namibia were investigated. For that purpose, magnetotelluric (MT) data were recorded at 167 land stations along a 140 km wide swath in northern Namibia and at 30 ocean bottom sites along a coast-parallel and a coast-perpendicular profile in the vicinity of the Walfis Ridge. 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 antiforms structures are highly conductive. Some of the features are unexpected, however, such as zones of high conductivity beneath the Congo Craton. The onset of the Congo Craton appears to be a well resolved feature in the gravity data while some of the high conductivity coincides spatially with magnetic anomalies. We therefore suggest using gravity and aeromagnetic data which are available from the Geological Survey of Namibia to obtain 2D and 3D potential field models. With this proposal, we intend 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 the SPP SAMPLE (phase II) as additional constraints, (iv) elaborate empiricalrelations between electrical conductivity and magnetization (density) 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 on the basis of all availablegeophysical data.