Abstract

Shales and siltstone samples from the Ikorongo Group of north-eastern Tanzania yield TDM ages of between 2049 Ma and 2597 Ma and ɛNd(0) ranging from ca. -28.3 to -17.3. These ages are interpreted as representing the mean mantle extraction ages of the protolith of the Ikorongo rocks. The data are consistent with most of the detritus being derived from lithologies of the Archaean Musoma-Mara Greenstone Belt. The TDM data also suggest participation of the Mozambique Belt rocks, although less in proportion when compared to the cratonic protolith. Mixing calculations indicate that the samples’ protolith can be modelled as mixtures of detritus from cratonic granitoids (42.2%) and andesites (40.4%) of the MMGB with those from Proterozoic granulites (17.4%) of the Mozambique Belt. The fact that the basin received material from the Pan-African Mozambique Belt, which is known to have cooled below ~300°C at about 540 Ma, points to a Cambrian or younger age for deposition of the Ikorongo strata.

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