Trace element and isotopic geochemistry of Cenozoic alkali basaltic lavas from Atakor (Central Sahara)

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The Late Miocene to Recent Atakor volcanic complex of the Hoggar (southern Algeria, central Sahara) is composed of alkali basalts and related rocks (mainly phonolites and trachytes). Most lavas have a restricted spread of their Sr and Nd isotopic ratios. ⁸⁷Sr/⁸⁶Sr ratios range from 0.70318 to 0.70422 and ¹⁴³Nd/¹⁴⁴Nd ratios range from 0.512776 to 0.512937. An exception is peralkaline trachyte which has the highest Sr (0.71271) and the lowest Nd (0.512593) isotope values and was formed by an assimilation-fractional crystallization process from basaltic magma. The basaltic rocks have trace element and isotopic compositions similar to ocean island basalts. It is suggested that the parent basaltic magmas were derived from a mantle plume which was modified during its ascent by interaction involving infiltration of a subcontinental lithospheric peridotite by plume-derived melts.