THE MOZAMBIQUE BELT IN NORTHERN MOZAMBIQUE - NEOPROTEROZOIC (1100-850-MA) CRUSTAL GROWTH AND TECTOGENESIS, AND SUPERIMPOSED PAN-AFRICAN (800-550-MA) TECTONISM

The Precambrian basement of northern Mozambique is composed mainly of high-grade gneiss, granulite, migmatite and orogenic plutonic rocks em placed and deformed during the Mozambican orogeny between 1100 and 850 Ma. Granulite nappes (Lurio Supergroup) were thrust over allochthonou s supracrustal units (Chiure Supergroup), and both sequences were then thrust over an autochthonous migmatitic foreland (Nampula Supergroup) . The granulite rocks are mostly of plutonic origin, and a model is pr oposed of an initial calc-alkalic enderbitic mass extracted from the m antle at approximately 1050 Ma and emplaced in the lower crust; this e nderbitic parent is considered as the source for successive alkali-ric h melts which were emplaced synkinematically between 1050 and 850 Ma. The supracrustal units comprise marine metasedimentary rocks, and calc -alkalic and tholeiitic rocks associated with ultramafic-mafic sequenc es and synkinematic granite. The autochthonous foreland consists mainl y of plutonic migmatite, showing low Sr initial ratios and originating from mantle-derived tonalitic rocks emplaced between 1100 and 9 50 Ma , associated with crustal-melt granite showing higher Sr initial ratio s and dated as late as 8 50 Ma. Major synmetamorphic shearing and blas tomylonitization, and regional thrusting to the east and southeast, ar e the main manifestations of the Mozambican orogeny. Early structures are preserved in the granulite complex and the migmatite foreland. Low -grade metasedimentary rocks (phyllite, sandstone, conglomerate and ma rble), with possible glacial affinities, unconformably overlie the Moz ambican basement and are correlated with the Katangan Supergroup. Thes e rocks, together with the basement, were caught up at approximately 5 38 Ma in Pan-African thrusts, transcurrent shear zones and folds in an intracontinental environment. These new data allow a reassessment of the entire Mozambique Belt, until now regarded as a Pan-African mobile belt involving variably remobilized cratons. The authors believe the belt to be a major fan-shaped collision zone between a Kalahari craton and an Indo-Antarctic craton.