Abstract

N Malawi includes two main groups of rocks, the Jembia River Granulites to the south and the Misuku Gneisses to the north. The latter are separated into two distinct units, the Chambo and the Songwe Gneisses. The region lies at the junction of the Ubendian, Irumide and Mozambique Orogenic Belts and an insight into the structural history of the area has been gained by mapping and Rb–Sr, K–Ar age determinations.

The Ubendian deformation (pre-1800 m.y.), which was accompanied by granite intrusions, produced the dominant SE structural trend. A subsequent Irumide deformation (c. 1100 m.y.) resulted in some weak N trending structures. The influence of the Irumide movements is believed to extend into S Tanzania.

The intrusion of the Songwe Syenite Complex (c. 700 m.y.) occurred during the initial Mozambique deformation. This caused the realignment of many Irumide structures and generated folds whose geometry was controlled by the pre-existing Ubendian structural trend. The Mozambique folding was associated with movement along several shear zones; these include the Mugesse Shear Zone which forms a tectonic junction between the Songwe and the Chambo Gneisses. This shear is a major line of weakness which originated during the Ubendian Orogeny and was reactivated by the Mozambique deformation and recent rift faulting.

A tentative correlation is made between the Misuku Gneisses and rocks of the Ubendian Belt in Tanzania.

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