Miocene igneous rocks (diorites. andesites, dacites, rhyolites and microgranites) of Chetaibi and Cap de Fer massif, NE Algeria, are high-K calc-alkaline to shoshonitic rocks. Fresh diorites have delta(34)S and delta(18)O values ranging between -2.5 parts per thousand and +5.9 parts per thousand, +6.5 parts per thousand and +6.7 parts per thousand respectively, indicating a mantle origin. The relatively low delta(34)S values (-5.47 parts per thousand to -12.2 parts per thousand) and high delta(18)O (+8.37 parts per thousand to +9.0 parts per thousand) of altered diorites indicate the input of a crustal component to the initial magma. The microgranites' I-type signature is indicated by the geochemical data and the delta(34)S and delta(18)O values of -1.2 parts per thousand and -3.6 parts per thousand and +7.8 parts per thousand to +10.4 parts per thousand respectively. The andesites show a large variation of delta(34)S, between -33.2 parts per thousand and +25.7 parts per thousand. Massive andesites with delta(34)S between +6.87 parts per thousand and +7.67 parts per thousand preserve a S-enriched mantle signature. The of the lava flows between +25.77 parts per thousand and +25.8 parts per thousand are attributed to open system magma degassing, whereas the low delta(34)S of two andesitic dyke samples (-13.7 parts per thousand and -33.2 parts per thousand) strongly suggest a crustal Sulphur input. High delta(18)O (+9.2 parts per thousand to + 15.7 parts per thousand) of andesites indicate post-magmatic alteration (mainly silicification); the flyschs with delta(18)O between of +13.3 parts per thousand and +21.7 parts per thousand are most likely the contaminant. Quartz veins within the andesites gave a delta(18)O Value of +23.0 parts per thousand while silica-filling vesicles yielded a value of +13.8 parts per thousand. Initial Sr-isotope data are rather high for all the rocks (diorites: 0.707-0.708, andesites: 0.707-0.710, and microgranites and rhyolites: 0.717-0.719), and because geochemical and stable isotope data do not indicate a substantial amount of crustal assimilation, an extensive enrichment of the mantle source by subducted sediments is called for. A metasomatized-mantle source, characterized by high radiogenic Sr and relatively high delta(18)O, has also been indicated for the genesis of similar Tertiary igneous rocks in the Western Mediterranean basin, e.g. the Volcanic Province of southeasten Spain [Benito, R., Lopez-Ruiz, J., Cebria, J.M., Hertogcn, J., Doblas M., Oyarzun, R., Demaiffe, D., 1999. Sr and O isotope constraints oil source and crustal contamination in the high-K calc-alkaline and shoshonitic neogene volcanic rocks of SE Spain. Lithos 46, 773-802] and some plutons of northeastern Algeria [Ouabadi, A., 1994. Petrologie, geochimie et origine des granitoides peralumineux cordierite (Cap Bougaroun, Beni-Touffout et Filfila), Algerie nord-orientale. These de Doctorat, Universite de Rennes I, France, 257p; Fourcade, S., Capdevila, R., Ouabadi, A., Martineau, F., 2001. The origin and geodynamic significance of the Alpine cordierite-bearing granitoids of northern Algeria. A combined petrological, mineralogical, geochemical and isotopic (O, H, Sr, Nd) study. Lithos 57, 187-216]. (c) 2005 Elsevier Ltd. All rights reserved.
