CONSTRAINED GRAVITY MODELS AND STRUCTURAL EVOLUTION OF THE ASHANTI BELT, SOUTHWEST GHANA

The Palaeoproterozoic terrane of southwest Ghana comprises a sequence of folded sedimentary/volcaniclastic rocks which separate a series of northeast trending volcanic belts. While the stratigraphy and structur e of the belts are similar, the Ashanti Belt is characterised by a mor e tectonised northwest margin along which most of the major epigenetic Au deposits in Ghana are located. Early models of the tectonic evolut ion of this belt, which generally invoked two phases of deformation, a re inconsistent with more recent structural and isotopic evidence (Eis enlohr and Hirdes, 1992). Modelling of regional gravity data by Hastin gs (1982) acknowledged the tectonic significance of the belt margins b ut lacked the benefit of constraints provided by more detailed mapping . This paper re-examines existing gravity data over the Ashanti Belt a nd presents constrained cross-sectional models which honour the mapped geology along the length of the belt and are consistent with the conc ept of a single, continuous deformational event. A synoptic scenario f or the large-scale structural evolution of the belt is proposed which has implications for the location and timing of Au mineralisation. (C) 1998 Elsevier Science Limited.