Iron- and Nickel Enriched Olivine from Phlogopite Harzburgite of the Bug Granulite Complex (Ukrainian Shield)

Abstract

An abundance of the trace elements has been determined in olivine of the Archean spinel-bearing phlogopite harzburgite enclave (sample UR17/2) from the Bug granulite complex of the Ukrainian Shield by SIMS analysis. Major elements were analyzed in the olivine by SEM-EDS and EPMA analysis. The olivine shows a homogeneous chemical composition: MgO — 45.20—45.64 wt.%, FeO — 13.66—14.23 wt.%, with Fo85—86 and Fe/Mn ratio of 68.3—68.6 which corresponds to the ratio of 60—70 in olivine of peridotites. Ni content in the UR17/2 olivine ranges from 4730 to 5612 ppm, which is higher than in olivine from mantle peridotites, high magnesium OIB and Hawaiian picrites. The olivine has average content of Ti — 20.6 ppm, Nb — 0.03 ppm, Zr — 0.32—0.60 ppm, the low total REE (0.1—0.5 ppm). The olivine crystallization temperature, calculated using an Al-in-olivine thermometer, corresponds to ~ 900°C. Enrichment in Fe and Ni is the main feature that distinguishes the UR17/2 olivine from other mantle-derived olivine. Сomposition of the UR17/2 olivine and host harzburgite indicates an influence of T, P, the oxygen fugacity and composition of parent magma on the partition coefficients of Fe and Ni. Сomposition and structure (degree of polymerization) of magma are the main factors responsible for the olivine enrichment by iron and nickel.