Rb-Sr isotope analyses of 19 samples from three “Younger Granites” along the southern margin of the Rhodesian craton in southern Africa yield a good isochron with an age of 2,630 ± 15 m.y. and an initial Sr87/Sr86 ratio of 0.7040 ± 0.0005 (1σ errors). This initial ratio is significantly higher than those of other Younger Granites farther north, but is indistinguishable from those of gneisses and an anatectic granite of similar age in the high-grade Limpopo mobile belt to the south. The three intrusive units studied could not have been formed by reworking of the ancient (ca. 3,500 to 3,600 m.y. old) crust of the craton, but could have been derived form a ca. 2,900-m.y.-old terrane, for which evidence is presented from the adjacent northern marginal zone of the Limpopo belt.

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