Northern Belt Zwankendaba

The northern volcanic terrane includes the Harare (Salisbury), Mount Darwin, Chipuriro (Sipo-lilo), Midlands (Silobela and Que Que), Chegutu (Gatoma), Bubi, Bulawayo, and parts of the Fila-busi and Gwanda greenstone belts. These contain a lower volcanic series overlain by a calc-alkaline suite of basalts, andesites, dacites, and rhyolites. Pyro-clastic, tuffaceous, and volcaniclastic horizons are common. Also common are iron formations, and other sedimentary rocks including slates, phyllites, and conglomerate. In the Bulawayo-Silobela area (Mulangwane Range), the top of the upper volca-nics include a series of porphyritic and amgdaloidal andesitic and dacitic agglomerate and other pyroclas-tic rocks.

u-Pb ages from felsic volcanics of the northern volcanic belt include 2.696, 2.698, 2.683, 2.702, and 2.697 billion years. Isotopic data from the Harare-Shamva greenstone belt and surrounding granitoids suggest that the greenstones evolved on older continental crust between 2.715 and 2.672 billion years ago. The age of deformation is constrained by a 2.667 billion-year-old syn-tectonic gneiss, a 2.664 billion-year-old late syn-tectonic intrusion, and 2.659 billion-year-old shear zone-related gold mineralization. Other posttectonic granitoids yielded U-Pb zircon ages of 2.649, 2.618, and 26.01 billion years. Isotopic data for the felsic volcanics suggest that the felsic magmas were derived from a melt extracted from the mantle 200 million years before volcanism and saw considerable interaction between these melts and older crustal material.

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