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 ca lc-alkaline, probable Tertiary rocks, evolved by feldspar-dominated fr actional crystallization of a basic magma. Trace elements and isotopic ratios of Sr (Sr-87/Sr-86(16.0) = 0.71947-0.72404) and detailed petro genetic modelling exclude the granites from being produced solely by s imple crystal fractionation of a basaltic magma and the similarities o f these ratios to those of the Edough biotite gneisses (Sr-87/Sr-86(16 .0) = 0.71840-0.73008) confirm a genetic link. We conclude that the Ed ough Tertiary magmatic rocks and perhaps many of the Tertiary igneous rocks of NE Algeria were produced by crystal fractionation of mantle-d erived basaltic magma which subsequently assimilated substantial amoun ts of crustal material of the type Edough biotite gneisses.