Experimental Evidence for Polybaric Differentiation of Primitive Arc Basalt beneath St. Vincent, Lesser Antilles

Abstract

Equilibrium crystallization experiments have been performed on a primitive high-MgO basalt (HMB) from Soufrie`re, St. Vincent, with three initial H2O contents (06, 23 and 45 wt %), at pressures of 04, 07, 10 and 13 GPa and temperatures from 1350 to 950C. Redox conditions, as determined by mXANES analysis of Fe3þ in experimental glasses, were 1–4 log units above the nickel–nickel oxide (NNO) buffer. The aim of the study was to explore the differentiation conditions that gave rise to the observed geochemical variation in lavas and plutonic (cumulate) xenoliths from St. Vincent.