Possible evidence for regional chemical heterogeneity of the Upper Mantle

The garnets of garnet-peridotite xenoliths that occur in the kimberlites of Southern Africa and the U. S. S. R. are shown to differ significantly in chemical composition. It has been demonstrated that the compositions of garnets of this type depend largely on the compositions of the media in which they grew (Rickwood, Mathias and Siebert, 1968), and thus it is concluded that the Upper Mantle in these two regions differs in chemical composition. Southern Africa is a chromiferous province and the U. S. S. R. is a ferric province.South African U.M.P. Publication No. 15.This paper was commenced whilst I was financed by the C. S. I. R. Upper Mantle Committee and is a contribution to the South African part of the Upper Mantle Project.