Copper partitioning between olivine and melt inclusions and its content in primitive island-arc magmas of Kamchatka

Abstract

Melt inclusions and hosting them highly magnesian olivine from rocks of Kamchatka and the Western Aleutian island arc were analyzed for copper content by LA-ICP-MS to determine the copper partition coefficient in primitive island-arc magmas. Based on measurements of 45 olivine–melt pairs, this coefficient was determined to be 0.028 ± 0.009 (2σ), which is the lowest value among previously published data. Mass-balance calculations of copper in a typical mantle peridotite using obtained partition coefficient indicate that its content in peridotite and primary mantle magmas is mainly determined by mantle sulfide. The Cu partition coefficient was also used to calculate the copper content in parental magmas of volcanoes of the Central Kamchatka Depression. Estimates obtained using copper content in phenocrysts of primitive olivine (Fo > 88 mol %) from these rocks are, on average, 139 ± 58 ppm (2σ), which exceed copper contents in primitive basalts (MgO > 8.5 wt %) of mid-ocean ridges (MORB 93 ± 31 ppm). This suggests the primary enrichment of Central Kamchatka magmas in copper and correlates with their more oxidizing conditions of formation as compared to MORB.