The petrology, geochemistry and petrogenesis of the Edough igneous rocks, Annaba, NE Algeria

Microgranites and rhyolites of the Edough complex, Annaba, NE Algeria are described. Their petrology and geochemistry indicate that these calc-alkaline, probable Tertiary rocks, evolved by feldspar-dominated fractional crystallization of a basic magma. Trace elements and isotopic ratios of Sr (⁸⁷Sr/⁸⁶Sr_16.0 = 0.71947−0.72404) and detailed petrogenetic modelling exclude the granites from being produced solely by simple crystal fractionation of a basaltic magma and the similarities of these ratios to those of the Edough biotite gneisses (⁸⁷Sr/⁸⁶Sr_16.0 = 0.71840−0.73008) confirm a genetic link. We conclude that the Edough Tertiary magmatic rocks and perhaps many of the Tertiary igneous rocks of NE Algeria were produced by crystal fractionation of mantle-derived basaltic magma which subsequently assimilated substantial amounts of crustal material of the type Edough biotite gneisses.