The significance of NE-SW parallel fractures in the West African Craton

Abstract

A vertical set of NE-SW trending, parallel fractures in the West African Craton reveals rifting adjustment resulting from isostatic uplift of the basement. The craton core is now a horst of Archaean rocks. Minor structures indicate that gold mineralization along the fractures is syn- to post-rifting. Several remarkable features are associated with the fractures. These features are apparent in directions perpendicular to the trend of the fractures, and to structures in the craton in general. Rock formations/units get progressively younger in the NW and SE directions, towards the mobile belts flanking the craton. Metamorphism decreases from granulites, in the core, to upper greenschist facies in both directions. Bauxite, manganese, alluvial gold and diamond deposits increase in prominence away from the core in both directions. The ultimate picture, in a traverse across the down-faulted blocks, is that of climbing stratigraphic stairs, with each step (block) exposing younger units. Thus, defining the overall stratigraphy of the craton requires a column for each block, with correlation across blocks made in upward rather than horizontal directions. -Author