OLIVINE LIQUID PARTITIONING OF VANADIUM AND OTHER TRACE ELEMENTS, WITH APPLICATIONS TO MODERN AND ANCIENT PICRITES

Abstract

The partitioning of V, Ti, Sc, Cr, Ni, Zn, Ga, Zr, La and Yb between olivine and coexisting basaltic and komatiitic liquids was measured at known fugacity of oxygen, f (O2). Olivine and glass were analyzed for trace elements using laser-ablation inductively coupled plasma – mass spectrometry (LA–ICP–MS). The purpose of the study was to further refine an empirical oxygen barometer for picritic magmas (>10% MgO) based on the comparison of the f (O2)-dependent behavior of V with that of other incompatible and immobile trace elements (Ti, Sc, Ga, Zr and Yb) along the liquid line of descent. Results of this study present an improvement on the earlier estimates of redox conditions that utilized this approach because the partition coefficients for V and other incompatible trace elements (Ti, Sc, Ga, Zr and Yb) are measured in the same bulk-compositions under the same experimental conditions, eliminating any previous bias or correlations. The advantages and limits of the approach are demonstrated in applications to modern Hawaiian picrites, Archean komatiitic lavas and lunar rocks. Uncertainties in the method are significant [about ± 0.5 log f (O2) units], but it is applicable to mafic suites having an igneous phase-assemblage altered by metamorphism, or without a phase assemblage to which more conventional estimates of redox conditions can be applied. In many cases, crucial estimates of the minimum f (O2) can be made for many terrestrial and extraterrestrial rocks in the geological record.