Dating basaltic volcanism in the Neoarchaean Sukumaland Greenstone Belt of the Tanzania Craton using the Sm-Nd method: implications for the geological evolution of the Tanzania Craton

Metabasalts from the Sukumaland Greenstone Belt of north western Tanzania yield a whole rock Sm-Nd isochron age of 2823 +/- 44Ma (initial epsilon(Nd) = 2.7, MSWD = 1.24). This age, which is interpreted as dating the eruption of the oldest mafic volcanics in the belt, is at the 95% confidence level indistinguishable from 2780 +/- 3 and 2808 +/- 3 Ma single zircon U-Pb ages previously reported from strati graphically higher rhyolitic pyroclastic rocks from the southern margin of the belt. The age equivalency suggests that the entire similar to5-7 km thick greenstone sequence that has been traditionally classified into a predominantly mafic lower part overlain by an upper part in which felsic volcanics and BIF predominate, was emplaced within a relatively short time interval not exceeding similar to44Ma. The Sm-Nd age of the metabasalts is significantly older than a published zircon U-Pb age of 2680 +/- 3 Ma obtained from a migmatitic gneiss on the southernmost fringe of the Sukumaland Greenstone Belt. This corroborates previous evidence that high-grade metamorphism in the Tanzania Craton postdates emplacement of the greenstones and is most likely associated with the regional emplacement of the large granitic bodies that intrude and flank the greenstones. (C) 2002 Elsevier Science B.V. All rights reserved.