Geochemistry, petrography and rock magnetism of the basalts of Phek district, Nagaland

Abstract

Basalts occur as sub-alkaline tholeiites in the Naga ophiolite belt. They bear an E-MORB affinity ascribed to aqueous fluid addition from a dehydrating oceanic crust in a supra-subduction zone during the Indo-Burma plate collision. They are commonly altered to spilite. They exhibit relatively poor REE fractionation with almost flat chondrite-normalized patterns. Eu-anomalies are not prominent, indicating the negligible role of plagioclase fractionation in their petrogenesis. Rock magnetic studies suggest that magnetite is the major magnetic mineral in these Upper Cretaceous basalts.