The South West Atakor Volcanic District (Hoggar-Algeria): Petrography and Mineralogy from the Taessa Lavas

Abstract

The Taessa lavas are located in the Atakor volcanic domain, (Hoggar Algeria). The Atakor district has undergone a significant magmatic activity during the Mio-plio-quaternary, which lead to the outpouring of massive amounts of alkaline lava. This magmatic activity resulted in the reactivation of the Pan-african orogenesis accidents that occured during the collision between the african and european continents (Liégeois in Plates, Plumes and Paradigms: Geological society of America Special Paper, pp. 379–400, [10]). The petrographic and mineralogical studies relating to the Taessa’s alkali basalts highlighted the persistence of two basaltic groups: olivine-pyroxene basalt and olivine-green-pyroxene basalt. They are mainly represented by magnesian olivines, whose crystallization process ended by 693 °C, according to the Fabriès geothermometer (Contr Mineral Petrol 69:329–336, [6]) olivine-spinel, pyroxenes (diop-side, augite and hedenbergite) which crystallized by 500– 1300°C (phenocrysts), and by 1100–1300 °C (micro-lites), according to Lindsley geothermometer (Pyroxene thermometry. American Mineralogist 68:477–493, [11]), plagioclases (andesine –labrador) and sanidine, Oxides (titano-magnetites and spinel).