The Mozambique Belt in northern Mozambique: Neoproterozoic (1100–850 Ma) crustal growth and tectogenesis, and superimposed Pan-African (800–550 Ma) tectonism

Abstract

Abstract The Precambrian basement of northern Mozambique is composed mainly of high-grade gneiss, granulite, migmatite and orogenic plutonic rocks emplaced and deformed during the Mozambican orogeny between 1100 and 850 Ma. Granulite nappes (Lurio Supergroup) were thrust over allochthonous 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 proposed of an initial calc-alkalic enderbitic mass extracted from the mantle at ∼1050 Ma and emplaced in the lower crust; this enderbitic parent is considered as the source for successive alkali-rich 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 sequences and synkinematic granite. The autochthonous foreland consists mainly of plutonic migmatite, showing low Sr initial ratios and originating from mantle-derived tonalitic rocks emplaced between 1100 and 950 Ma, associated with crustal-melt granite showing higher Sr initial ratios and dated as late as 850 Ma. Major synmetamorphic shearing and blastomylonitization, and regional thrusting to the east and southeast, are 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 marble), with possible glacial affinities, uncomformably overlie the Mozambican basement and are correlated with the Katangan Supergroup. These rocks, together with the basement, were caught up at ∼538 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 Kalahari craton and an Indo-Antarctic craton.