Petrography and Chemistry of Basalts from the Carlsberg Ridge

The petrography of the basalts collected in dredge hauls from the Carlsberg Ridge (3° 37' N and 64° 07' E) show systematic variations in their textural and mineralogical assemblages, from an outennost 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 P₂O₅ 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.