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.