Metamorphism in Deep-Seated Zones of Transcurrent Movement at Kungwe Bay, Tanganyika Territory

Deformed rocks developed in zones where transcurrent movements took place during a late stage of the Ubendian orogeny are described from Kungwe Bay, western Tanganyika Territory. In areas where the regional metamorphism was still continuing, the mineral assemblages developed in the movement zones are the same as those developing regionally. Cataclastic textures characterize such movement zones. In other parts of the district, where the regional metamorphism had apparently come to an end, the zones of concentrated movement contain both mylonites and certain fine-grained deformed rocks which show no obvious cataclastic features. Some of the latter have textures recalling those of hornfelses and contain minerals such as garnet and hornblende which have remained stable during the deformation and have grown porphyroblastically. It is considered that these rocks result from deformation of the crust at depth, resulting in a local high-grade dislocation metamorphism to which heat released during the movements may have contributed. The significance of the deformed rocks and of the transcurrent movement system in which they occur is discussed, and a possible analogy with active seismic belts of the present day is mentioned.