Comparison of geoelectric and seismic reflection models of the Zambezi Valley basins, northern Zimbabwe

Details Comparison of geoelectric and seismic reflection models of the Zambezi Valley basins, northern Zimbabwe Comparison of geoelectric and seismic reflection models of the Zambezi Valley basins, northern Zimbabwe

Sep 2000

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000geoji.142..898b&link_type=abstract

Geophysical Journal International, Volume 142, Issue 3, pp. 898-914.

Astronomy and Astrophysics

Astronomy

1

Electrical Conductivity, Magnetotellurics, Reflection Seismology, Sedimentary Basin

Scientific paper

The Mana Pools and Lower Zambezi Karoo sedimentary basins lie within the Zambezi mobile belt in northern Zimbabwe. The subsurface apparent resistivities measured at both locations are extremely low. Magnetotelluric (MT) data along a profile across part of the Lower Zambezi basin have been inverted using Rapid Relaxation Inversion (Smith & Booker 1991) to find the minimum structure needed to fit the data and compare with an earlier forward model. The resistivity models of both the Mana Pools and the Lower Zambezi basins are then compared with their structure revealed from seismic reflection data. The resistivity structure of the Mana Pools basin is well modelled as a series of different resistivity layers whose boundaries are defined by the seismic data. However, the resistivity structure of the Lower Zambezi basin cannot be matched easily to the seismic structure; additional structure with no seismic expression is required. There is a conductive feature in the two basins in the Upper Karoo sandstone layer that extends below the seismic basement beneath the Lower Zambezi basin. This indicates that the conductors may represent different types of features in the two basins, consistent with their proposed different tectonic origins. A resistive unit is present within the sediments in the Lower Zambezi basin that may represent intercalated basalt dykes, giving an anisotropic MT response. It has been suggested that there might be similar thin basalt layers within the sediments of the Mana Pools basin, but these could not be resolved by MT methods. The low resistivity of the basement, particularly beneath the Lower Zambezi basin, is remarkable and 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. The presence of the Lower Zambezi basin conductor at depths greater than the seismic basement is consistent with observations to the west, in the adjacent Damara mobile belt, where similar conductors have been seen in regions with no sedimentary cover.

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