Publication 165
An audio-magnetotelluric investigation of the Otjiwarongo and Katima Mulilo regions, Namibia
Share, P.-E., A.G. Jones, M.R. Muller, D.T. Khoza, M.P. Miensopust, and S.J. Webb
Abstract
As an additional opportunistic component to the southern
African magnetotelluric experiment, natural-source audiomagnetotelluric
(AMT) data were acquired during phase IV
to investigate the local-scale electric conductivity subsurface
structure in the Otjiwarongo and Katima Mulilo regions
(Namibia) as an aid in locating the installation points for
high-voltage direct current earth electrodes. The study showed
that the shallow subsurface of areas containing one measurement
site in the Otjiwarongo region and three sites in the Katima
Mulilo region have appropriate high conductivities for
the optimal placement of the earth electrodes. Both of the
AMT surveys are situated close to the edge of the orogenic
Neo-Proterozoic Damara mobile belt (DMB). Previous studies
all suggest the existence of a highly conductive midcrustal
zone, which correlates well with the spatial location of the
DMB. Two-dimensional inverse modeling of the Otjiwarongo
AMT data confirms the existence of the high-conductive zone
at midcrustal depths (10–15 km). The high conductivity of the
DMB is explained by the presence of interconnected graphite
in the marble units present. The Katima Mulilo inversion results
are characterized by a conductive upper crustal layer that
does not form part of the DMB conductive belt. It was deduced
that at the uppermost subsurface (maximum ~200 m), Kalahari
sediments are responsible for the high conductivity observed,
whereas at greater depth (up to 6 km), its cause
remains enigmatic, albeit the hypothesis of ironstone or graphite
being present and causing the observed conductive upper
crust.
Source
Geophysics, 79, B151–B171, doi:10.1190/GEO2013-0171.1. Geophysics Case History. [PDF]
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Alan G Jones / 28 May 2014 /
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