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Geology and correlation of the central Irumide belt

2002; Elsevier BV; Volume: 35; Issue: 3 Linguagem: Inglês

10.1016/s0899-5362(02)00149-5

1879-1956

Bert De Waele, Benjamin Mapani,

earthquake and tectonic studies

The Irumide Fold belt of Zambia consists of a Palaeo to Mesoproterozoic complex of gneisses and granite gneisses and a supracrustal sequence of quartzites and pelites. Although no direct correlation is possible, the metasedimentary sequence is tentatively equated with the Manshya River Group described in the NE. The basement to the Irumide belt consists of the Bangweulu Granites to the North, and the Mkushi gneiss basement (MGB) to the Southwest. Age constraints on the Bangweulu Block are limited, but the Mkushi Gneiss has been dated at ∼2050 Ma. A detrital provenance study on a quartzite of the Manshya River Group near Mkushi indicates derivation from terranes of up to 3180 Ma, with a maximum age for the Manshya River Group set by the youngest detrital grain at 1941 Ma. Detrital cores from paragneisses and migmatites in the Serenje area indicate a more uniform detrital source for the sedimentary protolith of 2050–2000 Ma. A more direct age constraint on the Manshya River Group has been provided through an age of 1880 Ma on a concordant rhyolite in the metasedimentary sequence near Chinsali. The Manshya River Group consists of a succession of four pelite and four quartzite Formations. The granitoids, which make up a large portion of the Irumide belt, can be subdivided into an older suite of leucocratic gneisses and biotite-granites, and a younger suite of alkaline, often porphyritic K-feldspar granites. Oversimplified lithostratigraphic division of the "crystalline basement" in the southwest of the Irumide belt has lead to an overestimation of the Palaeoproterozoic basement (MGB). The extent of the Palaeoproterozoic basement awaits re-evaluation through fieldwork. The main structural trend of the Irumide belt is northeast and is related to extensive crustal shortening during the main stage of the Irumide orogeny. Tectonic transport is directed towards the northwest, with southwest directed backthrusting locally developed to define a double verging overall structure. The compressional stage is characterised by amphibolite grade metamorphism and accompanied by widespread granite magmatism and anatexis.