Mantle deformation beneath southern Africa

Seismic anisotropy from the southern African mantle has been inferred from shear-wave splitting measured at 79 sites of the Southern African Seismic E xperiment. These data provide tile most dramatic support to date that Arche an mantle deformation is preserved as fossil mantle anisotropy. Fast polari zation directions systematically follow the trend of Archean structures and splitting delay times exhibit geologic control. The most anisotropic regio ns are Late-Archean in age (Zimbabwe craton, Limpopo belt, western Kaapvaal craton), with delay times reduced dramatically in off-craton regions to th e southwest and Early-Archean regions to the southeast. While thin lithosph ere can account for weak off-craton splitting, small or vertically incohere nt anisotropy is a more likely explanation for tile Early-Archean region. W e speculate that this difference in on-craton anisotropic structure is tile result of two different continent-forming processes operating.