¹MINERALOGISCH-PETROGRAPHISCHES INSTITUT, UNIVERSITÄT KIEL, 24098 KIEL, GERMANY ²MAX-PLANCK-INSTITUT FÜR CHEMIE, POSTFACH 3060, 55020 MAINZ, GERMANY

RECEIVED APRIL 1, 1997; REVISED TYPESCRIPT ACCEPTED DECEMBER 3, 1997

Combination of Nd and Sr model ages and Pb isotopes on leached feldspars reveals distinct model age provinces not recognized previously within the Mozambique Belt of Tanzania. Most boundaries of these age domains are overprinted by Neoproterozoic (Pan-African) tectonism and metamorphism. Granitoids from the Archean craton show Nd model ages of 2·7-3·1 Ga and very primitive Pb isotope systematics in feldspars. Amphibolite-facies migmatites and granulites from the Mozambique Belt have similar characteristics, yet their high ²⁰⁸Pb/²⁰⁴Pb values point to U loss in the Archean, possibly during high-grade metamorphism, and subsequent Pan-African reworking. Eclogite-facies metapelites of the Early Proterozoic Usagaran Belt likewise exhibit Archean Nd model ages, but higher Pb isotopic ratios are consistent with last recrystallization of feldspar at 2 Ga. Granulites with Nd model ages from 1 to 1·5 Ga only occur in NE Tanzania; because of their restricted range in Pb isotopic composition they are interpreted as juvenile additions during late Proterozoic time. Granulites of the W Uluguru Mts have Nd model ages between 2·1 and 2·6 Ga, and highly variable feldspar Pb isotope composition indicating possible derivation from cratonic and/or Usagaran material, reworked and mixed with a small pr