The geological evolution of the Magondi Mobile Belt, Zimbabwe

Abstract

Abstract The Zimbabwe Archaean craton is flanked to the NW by the Magondi Mobile Belt. Within this belt, Magondi Supergroup volcanics and sediments were deposited during the early Proterozoic before being deformed and metamorphosed ∼ 1850 Ma ago. In the south, the belt is a typical thin-skinned thrust belt with Magondi Supergroup rocks thrust SE onto the Archaean craton. Northwards, the character of the belt changes with the structural style changing to a more thick-skinned type, metamorphic grade increasing from greenschist to granulite facies and with increasing amounts of early Proterozoic basement gneisses imbricated within the sedimentary sequence. Metamorphism in the northern part of the belt is explained by thermal relaxation after the overthrusting of hot early Proterozoic rocks from the west effectively sandwiching the Magondi rocks between Archaean basement below and allochthonous early Proterozoic basement above. Flat-lying isograds that date from this event were subsequently folded along S-plunging axes during continued orogenic squeezing. The rocks within the Magondian belt are essentially unaffected by subsequent Pan-African deformation and metamorphism. The evolution of the belt seems to fit the emerging pattern of cratonisation of the African plate, within which pattern the Magondian Mobile Belt may be correlated with other ‘Eburnian’ cycle belts in South Africa but not with any of the tectonothermal provinces to the north of the Pan-African Zambezi-Damara Belt.