The composition of melt and fluid inclusions in spinel of peridotite xenoliths from Avacha volcano (Kamchatka)

Abstract

This work considers the studies of melt and fluid inclusions in spinel of ultramafic rocks in the mantle wedge beneath Avacha volcano (Kamchatka). The generations of spinel were identified: 1 is spinel (Sp-I) of the “primary” peridotites, has the highest magnesium number (#0.69–0.71), highest contents of Al2O3 and lowest contents of Cr2O3 (26.2–27.1 and 37.5–38.5 wt %, respectively), and the absence in it of any fluid and melt inclusions; 2 is spinel (Sp-II) of the recrystallized peridotites, has lower magnesium number (Mg# 0.64–0.61) and the content of Al2O3 (18–19 wt %), a higher content of Cr2O3 (45.4–47.2 wt %) and the presence of primary fluid inclusions; 3 is spinel (Sp-III) that is characterized by the highest content of Cr2O3 (50.2–55.4 wt %), the lowest content of Al2O3 (13.6–16.6 wt %), and the presence of various types of primary melt inclusions. The data obtained indicate that metasomatic processing of “primary” peridotites occurred under the influence of high concentrated fluids of mainly carbonate-water-chloride composition with influx of the following petrogenic elements: Si, Al, Fe, Ca, Na, K, S, F, etc. This process was often accompanied by a local melting of the metasomatized substrate at a temperature above 1050°C with the formation of melts close to andesitic.