The geochronology of the Tanzanian Shield.

Abstract

New whole-rock Rb-Sr isochron dates from the Tanzanian Shield of E Africa fall in the range 2500+ -100Ma and outline a major period of granitoid magmatism that has not, until now, been documented from this part of the African continent. Although at least two events can be delineated, one at 2740Ma, the other at 2540Ma, the younger is more widespread and reflects extensive granitoid magmatism throughout large areas of Tanzania, SE Uganda and W Kenya. Lacking ages greater than 2800Ma, the Tanzanian Shield is unique among the Archaean cratons of Africa. Initial 87Sr/86Sr ratios lie typically between 0.7010 and 0.7020, similar to late Archaean igneous rocks in other crations, and provide little evidence to support the origin of the 2500Ma Tanzanian crustal segment by simple reworking of ancient continental crust.-Authors Show more