Petrogenetic analysis of fluid and melt inclusions in minerals from mantle xenoliths from the Bele pipe basanites ( North Minusa depression)

Abstract

Results of study of different types of inclusions in minerals from mantle xenoliths from the Bele pipe basanites are presented. Two groups of inclusions were recognized in the host minerals according to their genesis. The first group includes single, apparently primary, fluid inclusions. They were discovered only in orthopyroxenes and consist of CO 2 (95 mol.%) and N 2 (5 mol.%). These inclusions had partly leaked. The densities of two least leaked inclusions from different xenoliths are 1.05 and 1.14 g/cm 3, and their trapping pressures are estimated at >8.5 and 12 kbar, respectively. The second group includes syngenetic secondary fluid, melt, and crystalline inclusions. In composition the secondary fluid inclusions differ from the primary ones in higher concentrations of N 2 (up to 7 mol.%). Their maximum density is 0.57 g/cm 3, which corresponds to 2.4–2.6 kbar and 1100–1200 °C (homogenization temperature of secondary melt inclusions). Comparison of data on melt inclusions in xenolith minerals and host-basanite phenocrysts shows that the secondary inclusions in the xenoliths are, most likely, the result of infiltration and partial reaction of basanitic melt with the xenoliths. On the ascent, the basanitic melt vigorously reacted with mantle xenoliths, which led to the appearance of secondary inclusions in nodule minerals at shallow depths and interstitial mineral assemblages in the xenoliths.