Tectonometamorphic Evolution of the Chewore Inliers: Partial Re-equilibration of High-grade Basement during the Pan-African Orogeny

Abstract

only minor structural reworking during M2. Granulite Terrane The Chewore Inliers are isolated outcrops of the Zambezi Mobile samples within 2 km of the basal thrust margin preserve M1 Belt within the Mesozoic Lower Zambezi Rift Valley in Zimbabwe. mineral assemblages but these minerals were chemically re-equiDetailed mapping has recognized four terranes: the Zambezi, librated without recrystallization during M2 at conditions of 5·6 Quartzite, Granulite and Ophiolite Terranes. Apart from the ± 1·5 kbar and 631±100°C. Granulite Terrane samples were Ophiolite Terrane, all are dominated by supracrustal gneisses with totally recrystallized in shear zones at the margin of this terrane. concordant granitic orthogneiss units of 1071 ± 8 and 1083 ± These samples equilibrated at conditions identical to the peak of 8 Ma age. These terranes experienced low-P–high-T metamorphism M2, at 7·7± 1·9 kbar and 590± 110°C. The re-equilibrated (M1) terminated by isobaric cooling at 945 ± 34 Ma. M1 and recrystallized sample sets define two points on the clockwise assemblages of sillimanite–spinel–garnet, garnet–orthopyroxene and P–T path experienced by the Granulite Terrane during further two-pyroxene mafics are recorded in the Granulite Terrane, and burial and reworking in the Pan-African Orogeny, and are consistent conditions of formation were 4·4 ± 1·7 kbar and >800°C. M1 with the M2 P–T path documented for the other terranes. mineral parageneses and associated ductile deformation structures dominate the Granulite Terrane, but M1 mineral parageneses are only preserved as sillimanite–spinel inclusions in garnet cores in the other terranes. The Zambezi, Quartzite and Ophiolite Terranes were almost totally recrystallized during reworking in the M2