The chemistry and petrology of basalts from leg 37 of the Deep-Sea Drilling Project

Abstract

This paper presents combined major element, trace element, and petrographic data on 108 samples from sites 332, 334, and 335 of DSDP (Deep-Sea Drilling Project) leg 37. The 102 basalt samples have characteristics of midocean tholeiites but exhibit wide compositional variation ranging from ‘normally’ LREE (light rare earth element) depleted to ‘anomalous’ LREE enriched compositions. We have distinguished five basalt types on the basis of major elements. The olivine phyric basalts type IV (site 332) with characteristics (Mg/(Mg + Fe) ∼ 0.7, Ni ∼ 250 μg/g, and Sc ∼ 35 μg/g) indicative of primitive magmas can be related to plagioclase accumulative basalts (type II) and picrites (type III) by simple addition of plagioclase and olivine. Plagioclase phyric basalts (type I) characterized by lower Mg/(Mg + Fe) (≃0.50–0.65) at sites 332 and 335 are not related by fractional crystallization to a common parent or to each other. The plagioclase phyric type V basalts recovered from site 334 are not related to type I basalts or to a common parental magma by fractional crystallization processes. Several parental magmas derived from an inhomogeneous mantle are required.