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

Abstract

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. 8, 7Sr/36Sr ratios range from 0.70318 to 0.70422 and l43Nd/l44Nd 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 ele-ment 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 involv-ing infiltration of a subcontinental lithospheric peridotite by plume-derived melts. © 1993, GEOCHEMICAL SOCIETY OF JAPAN. All rights reserved.