An overview of phase chemistry and magmatic evolution in the Cretaceous flood basalt province of northern Madagascar

The Cretaceous flood basalts of northern Madagascar range in composition from picritic basalt to basaltic andesite with a serial affinity ranging from tholeiitic to slightly alkaline. Rare, more evolved rocks are represented by peraluminous rhyodacites and peralkaline rhyolites. The intrusive complexes have a large range of lithologies, from ultramafic (dunites, wehrlites, clinopyroxenites) to felsic (leucogabbros, syenites). We report here the chemical composition of olivine, Ca-rich and Capoor pyroxene, feldspar, Fe-Cr-Ti oxide, amphibole, glass and accessory phases; the significance of their variations for what concerns geothermobarometry and regional chemical correlations is also discussed. The evolution from the least to the most evolved compositions, and from the whole rocks towards the interstitial glasses, which are thought to be lowpressure residual liquid compositions, has been modelled with fractionation of the observed phases, leaving Mg- to Fe-rich gabbroic solids.