Petrography and chemistry of basalts from the Carlsberg ridge

Abstract

The petrography of the basalts collected in dredge hauls from the Carlsberg Ridge (3 degrees 37'N and 64 degrees 07'E) show systematic variations in their textural and mineralogical assemblages, from an outermost vitreous glassy to a holocrystalline interior through a variolitic zone. The silica-alkalies relation show these basalts to be of sub-alkaline nature. Variable normative compositions and Mg number, increase in alkali index, differences in Al2O3/CaO and FeO/MgO ratios, variable trace element concentrations, together with variable relations of P2O3, TiO2, Ni and Cr with MgO indicate a process of fractional crystallisation of a primary magma. Chemically and mineralogically these rocks have a closer affinity to those of the other parts of the Mid-Indian Ocean Ridge