A magnetotelluric model of the Mana Pools basin, northern Zimbabwe

The Mana Pools sedimentary basin lies within the Zambezi mobile belt in nor thern Zimbabwe. New and preexisting magnetotelluric data and the available seismic reflection data are used to constrain the basin structure and the d epth to the electrical basement. Long-period magnetotelluric (LMT) data wer e collected at five stations along a 60 km north-south profile across the M ana Pools basin and onto the southern escarpment. These data augment an exi sting audio:Frequency (AMT) data set from 11 sites in the same area. The su bsurface apparent resistivities measured at periods sampling the basin are very low (a few Omega m). After processing both data sets, the estimated im pedance tensor is decomposed, showing that the resistivity structure of the Mana Pools basin can be modeled two dimensionally. The rho(+) algorithm is used to show that there is no systematic offset in magnitude between the A MT and LMT data sets before they are combined. Minimum structure resistivit y models of the Mana Pools basin compare well with the information from ref lection seismic data and support its previous description as a half graben basin of similar to 7 km depth. The excellent conductor in the Mana Pools b asin is quite different to those seen elsewhere in the orogenic belt in tha t it is a feature of the sedimentary fill rather than the basement. The res istivity of the basement is low but no localized good conductor is observed ; these low resistivities may result from a high degree of either chemical or tectonic alteration to the underlying rocks due to metamorphic processes and tectonic disruption during rift formation.