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The internal structure and geotectonic setting of the Xade and Tsetseng complexes in the western most part of the Kaapvaal Craton.

British Geological Survey, West Mains Road, Edinburgh, Scotland, United Kingdom, EH9 3LA Geosoft Europe Limited, Wallingford, United Kingdom, OX10 0AD e-mail: gaud.pouliquen{at}geosoft.com

R.M. Key and A. Walker

British Geological Survey, West Mains Road, Edinburgh, Scotland, United Kingdom, EH9 3LA. e-mail: rmk{at}bgs.ac.uk

The Xade Complex is an unexposed Y-shaped body, approximately 100 km long and 25 km wide, located close to the western margin of the Kaapvaal craton in Botswana. The complex is characterized by large coincident magnetic and gravity anomalies. It is completely covered by varying thicknesses of Kalahari sediments as well as by Karoo strata, which means that detailed analysis of high resolution airborne magnetic data, ground gravity data and limited seismic data are essential in interpreting the internal configuration of the complex. An earlier interpretation of the first airborne magnetic survey of Botswana (Reeves, 1978) coupled with subsequent drilling discovered the Xade Complex and showed that it is made up of mafic and ultramafic rocks. However, the limited amount of drilling did not provide sufficient information to either interpret in detail its internal geology or its regional geotectonic setting (Meixner and Peart, 1984). New 2D and 3D gravity and magnetic field modelling have constrained the geometry of the complex as a syncline defined by folded mafic lavas and high-level sub-volcanic mafic sheets. The Xade Complex lies within a graben that forms the north-south arm of a triple junction with the faulted western margin of the Kaapvaal Craton. The focal point of the triple junction coincides with an inflection of the cratonic margin and is the likely site of the feeder zone to the mafic lavas of the Xade Complex. The Tsetseng Complex is shown to be an internally layered, magnetite-bearing gabbro.