Area selection for diamonds using magnetotellurics: Examples from southern Africa

Abstract

30Southern Africa, particularly the Kaapvaal Craton, is one of the world's best natural 31 laboratories for studying the lithospheric mantle given the wealth of xenolith and seismic data 32 that exist for it. The Southern African Magnetotelluric Experiment (SAMTEX) was launched 33 to complement these databases and provide further constraints on physical parameters and 34 conditions by obtaining information about electrical conductivity variations laterally and with 35 depth. Initially it was planned to acquire magnetotelluric data on profiles spatially coincident 36 with the Kaapvaal Seismic Experiment, however with the addition of seven more partners to 37 the original four through the course of the experiment, SAMTEX was enlarged from two to 38 four phases of acquisition, and extended to cover much of Botswana and Namibia. Comparisons between the resistivity image maps and seismic velocities from models 49 constructed through surface wave and body wave tomography show spatial correlations 50 between high velocity regions that are resistive, and low velocity regions that are conductive. 51In particular, the electrical resistivity of the sub-continental lithospheric mantle of the 52 Kaapvaal Craton is determined by its bulk parameters, so is controlled by a bulk matrix 53 property, namely temperature, and to a lesser degree by iron content and composition, and is 54 not controlled by contributions from interconnected conducting minor phases, such as 55 graphite, sulphides, iron oxides, hydrous minerals, etc. This makes quantitative correlations 56 between velocity and resistivity valid, and a robust regression between the two gives an 57 approximate relationship of Vs [m/s] = 0.045*log(resistivity [ohm.m]). 58 59

Making and Breaking of a Continent: Following the Scent of Geodynamic Imprints on the African Continent Using Electromagnetics

“…With this approach Weckmann et al (2003a) were able to resolve the internal structure of one of the major faults within the Damara Belt (Namibia). Jones et al (2009) used an alternative approach in order to image large tectonic units rather than internal details of more confined tectonic features. The authors calculated Niblett-Bostick (e.g.…”

Imaging the electrical lithosphere of South Australia - 2D profiles and preliminary results of AusLAMP SA

“…The data is used for 1D Niblett-Bostick depth transformations (Niblett and SaynWittgenstein, 1960;Jones et al, 2009b) which will give a qualitative view of the crustal and lithospheric structure at depth (Figure 1). Rigorous preliminary 3D models are calculated using non-linear conjugate gradient methods (Egbert and Kelbert, 2012).…”

An audio-magnetotelluric investigation of the Otjiwarongo and Katima Mulilo regions, Namibia

“…MT data were recorded at more than 740 locations covering an area that exceeds 1,000,000 km 2 (Jones et al, 2009b). The consortium members that formed SAMTEX come from academia, government, and industry (see the Acknowledgments in Jones et al, 2009b).…”

“…Furthermore, the conductivity models were used to make inferences about the thermal, mechanical, and chemical properties of the geologic terranes (Fullea et al, 2011) and to provide control on laboratory measurements of water in olivine . The correlation between diamond prospectivity and regional resistive/conductive boundaries in Namibia and South Africa has also been examined with SAMTEX results (Jones et al, 2009b;Muller et al, 2009).…”