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Geochemical mapping of North and Central Madagascar was carried out using stream sediments at an average density of one sample per 11 km2. Over 50 elements were determined from some 13,300 stream sediments using a sample size fraction of <150 μm following hot aqua regia digestion. Partially extractable concentrations of six major elements and seven base metals reveal that the Andriamena `greenstone' Belt of the Tsaratanana Complex is geochemically distinct from the other geological divisions within the Precambrian basement of central and northern Madagascar. In particular, this study has shown the detailed spatial distribution of anomalous concentrations of base metals which confirm known areas of chromite mineralisation within the Andriamena Belt. Base metal anomalies also occur in relation to Cretaceous and Neogene volcanic rocks, for example at Nosy Be, and mafic-ultramafic intrusions such as along the Maroala deformation zone. The distribution of anomalous Au in stream sediments showed good correspondence with known gold districts of central and northern Madagascar. Highest concentrations were measured in stream sediments from within the Ampasary-Mananjary (southern Androna-Mandritsara) and Andavakoera (northern margin of North Bemarivo) gold districts. The results of the stream sediment geochemistry show that these new data provide valuable information for current and future mineral exploration and environmental studies in Madagascar, at both regional and local scale.

New detrital zircon U-Pb age data obtained from various quartzite units of three spatially separated supracrustal packages in central and northern Madagascar, show that these units were deposited between 1.8 and 0.8. Ga and have similar aged provenances.

Late tectonic, post-collisional granite suites are a feature of many parts of the Late Neoproterozoic to Cambrian East African Orogen (EAO), where they are generally attributed to late extensional collapse of the orogen, accompanied by high heat flow and asthenospheric uprise. The Maevarano Suite comprises voluminous plutons which were emplaced in some of the tectonostratigraphic terranes of northern Madagascar, in the central part of the EAO, following collision and assembly during a major orogeny at ca. 550 Ma. The suite comprises three main magmatic phases: a minor early phase of foliated gabbros, quartz diorites, and granodiorites; a main phase of large batholiths of porphyritic granitoids and charnockites; and a late phase of small-scale plutons and sheets of monzonite, syenite, leucogranite and microgranite. The main phase intrusions tend to be massive, but with variably foliated margins. New U–Pb SHRIMP zircon data show that the whole suite was emplaced between ca. 537 and 522 Ma. Geochemically, all the rocks of the suite are enriched in the LILE, especially K, and the LREE, but are relatively depleted in Nb, Ta and the HREE. These characteristics are typical of post-collisional granitoids in the EAO and many other orogenic belts. It is proposed that the Maevarano Suite magmas were derived by melting of sub-continental lithospheric mantle that had been enriched in the LILE during earlier subduction events. The melting occurred during lithospheric delamination, which was associated with extensional collapse of the East African Orogen.