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Amadeu Muchangos C., Eduardo Mondlane University (Mozambique)
Salvadore Mondlane Jr. , Eduardo Mondlane University (Mozambique)
Daud Jamal L., Eduardo Mondlane University (Mozambique)
Daniel Ibraimo L., Eduardo Mondlane University (Mozambique)
L. Jeque A., Eduardo Mondlane University (Mozambique)
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The Archaean Manica Mutare Odzi (MMO) greenstone belt of Zimbabwe Craton was formed between 3.1 and 2.6 Ga, it has a synform structure with its fold axis plunging shallowly to the east. The structure comprises a volcano-sedimentary sequence of the Upper Bulawaian at the margins and Shamvaian meta-sediments (shallow water origin) in the core. To the east, the belt is bound by Archaean granitic gneisses and a N-S trending belt of Proterozoic gneisses of the Bárue Complex and quartzites and pelites of the Frontier Formation. The geology of MMO greenstone belt is dominated by shear zones occurring at the contacts between upper Bulawayan and the Mbeza metasedimentary rocks and within ultramafic units.
The mafic and ultramafic rocks have been assigned to the Bulawayan Supergroup on the basis of field relationships similarities. In the Manica (Mozambique) section of the belt these lithologies are referred to as the Macequece Formation. The Macequece Formation comprises peridotites, serpentinites, talc and chlorite schists, komatiitic and picritic metabasalts with discontinuous intercalations of BIF. The clastic rocks have been assigned to the Shamvaian Supergroup and are referred to as the Mbeza-Vengo Formation. The Mbeza-Vengo Formation is composed of basal conglomerate, polimict coglomerate/sandstone, siltstones, greywackes, slates, phyllites and grits. The presence of komatiitic basalt pebbles, BIF and minor granitic clasts in the basal conglomerate suggests that the Mbeza - Vengo metasedimentary rocks mainly originated from erosion of immediately underlying greenstone lithologies and old basement.
The entire sequence was deformed by intrusion of post tectonic granites, which caused contact metamorphism in the greenstones, and probably local growth of biotite in the Mbeza sediments. The intrusion of late granites and the related metamorphism represent the last significant deformation phase in the Archaean. In the Proterozoic, the MMO greenstone belt and surrounding granites were fractured and intruded by dolerite dykes mainly NE and NW trending and related sills.
Three main groups of mafic dikes were indicated intruding the granite- greenstone terrains East of the Zimbabwean Craton. These include mafic dikes in the MMO greenstone belt, meta-dolerites in the Archaean granitic-gneisses and meta-sediments of the Gairezi Group and the dolerites dikes and sills of the Mashonaland in the Umkondo quartzites. The Sm/Nd dating gives an age of 1783±51 for the MMO dolerites, 1102±52 Ma for the Umkondo dolerites and 973±73 Ma for the meta-dolerites in the Archaean granitic-gneisses.
The present study concentrates on the establishment of the spatial relationships between the mafic intrusions and the greenstone - granitic-gneiss hosts, the petrography of the dolerites and the age relationship.
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