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Ane K. Engvik, Geological Survey of Norway (Norway)
Bernard Bingen, Geological Survey of Norway (Norway)
Einar Tveten, Geological Survey of Norway (Norway)
Giulio Viola, Geological Survey of Norway (Norway)
Joachim Jacobs, University of Bergen (Norway)
Elias Daudi, National Directorate of Geology of Mozambique, Mozambique (Mozambique)
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NE Mozambique exposes a deeply eroded high-grade segment of the East African Orogen, showing widespread granulite-facies lithologies. Granulites were investigated as part of a geological mapping project, with special focus on the Lurio Belt, a possible Pan-African suture zone. Results are summarized here from the foreland (NW) to the hinterland (SE) of the orogen. (1) In the foreland, the Ponta Messuli Complex shows evidence for a Palaeoproterozoic (1950 Ma) granulite-facies metamorphism. Migmatitic metapelitic gneisses are characterized by the assemblage Grt+Sil+Spl+Crd+Bt+Mag/Ilm, providing PT estimates of 0.7 GPa above 700°C. (2) The Mesoproterozoic Unango and Marrupa Complexes show geochronological evidence for a late-Grenvillian metamorphism (950 Ma) and a Pan-African (550 Ma) increasingly pervasive SW-wards towards the Lurio Belt. Widespread intermediate-P charnockites in the Unango are attributed to the first event. A few occurrences of high-P granulites are reported in the NW part of this complex, including Ky+Rt-bearing quartzites and mafic granulites. These show the assemblage Grt+Cpx+Pl+Qtz+Ts+Rt recording 1.50 GPa-820°C, but are undated and their significance is difficult to assess. In the southern part of the Unango Complex, Pan-African Opx+Grt+Pl+Qtz+Bt granulites and Sil+Grt-bearing metapelites indicate 0.7 GPa->800 °C. (3) A stack of Pan-African nappes overlay the Unango and Marrupa Complexes. It is characterized by early Pan-African metamorphism at 735 Ma and 630-610 Ma. A Grt+Opx+Pl+Qtz+Bt+Ilm banded granulite pins PT conditions of 1.09 GPa-810°C at 735±4 Ma in a large enderbite in the Xixano Complex. Grt+Cpx-bearing amphibolites in this complex (0.57 GPa->700°C) and Sil-bearing metapelites probably record a younger amphibolite facies overprint (630-610 Ma?). Undated mafic granulites in the M'Sawize complex yield estimates of 1.15 GPa->800°C. (4) The Lurio Belt is a NNE-trending linear structure reworking the Unango, Marrupa and the nappe complexes. It is cored by a granulite-facies mélange, the Ocua Complex, showing consistent evidence for peak conditions above 1.0 GPa between 580 and 540 Ma. Mafic boudins at one locality preserve a Grt+Cpx+Pl+Qtz high-P granulite-facies assemblage equilibrated at 1.6 GPa-950°C-557±16 Ma. Pl+Opx-bearing corona around garnet attests to rapid near-isothermal decompression, while a Pl+Amp-corona records subsequent cooling into amphibolites facies. The high-P granulites in the Lurio Belt demonstrate burial of crust to at least 55 km followed by rapid exhumation during the final stage of Pan-African convergence. (5) South of the Lurio Belt, the Nampula Complex is characterized by a late Pan-African, poorly evaluated, high-grade metamorphism between 550 and 490 Ma, coeval with widespread granite plutonism. The investigation of NE Mozambique shows that high-T metamorphism and high-P granulite facies conditions were achieved through a long periode from the Palaeoproterozoikum to early Palaeozoikum.
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