ZINC IN SPINELS OF PERIDOTITE XENOLITHS FROM PLIOCENE BASANITES OF THE VITIM VOLCANIC FIELD

Abstract

A group of low-temperature peridotites with equigranular mosaic texture is distinguished among spinel peridotite xenoliths from Pliocene basanites of the Dzhilinda River. The mineral compositions of these peridotites are characterized by some anomalous features. At a generally highly magnesian composition (Mg# = 91), peridotites are enriched in pyroxenes and spinel and contain 47.4% olivine, 28% orthopyroxene, 21% clinopyroxene, and 3.6% spinel, on the average. Clinopyroxene has 1.8-2.2% TiO2. Olivine contains up to 0.8% NiO. Spinel is characterized by high concentrations of ZnO = 0.8-0.95%, NiO = 0.6-0.8%, and V2O5 = 0.3-0.4%. These data allow us to assume that the peridotites were originated by an influence of a specific metasomatic agent on a depleted peridotite protolith. Metasomatic fluid or melt was strongly enriched in Ti and Zn and, to a lesser degree, in Al, Na, and Ca. Metasomatism and accompanied subsolidus recrystallization lead to the redistribution of elements among phases and anomalous enrichment of spinel in Zn and Ni, olivine in Ni, and clinopyroxene in Ti.