Kaersutite-Bearing Xenoliths and Megacrysts in Volcanic Rocks from the Funk Seamount in the Southwest Indian Ocean

Abstract

Eight samples (seven volcanic rocks and one quartz sandstone) have been dredged from the Funk Seamount, 60 km NW of Marion Island in the southwest Indian Ocean Oat. 46 ~ 15' S, long. 37 ~ 20' E). The volcanic rocks are fine-grained vesicular basanitoids and glass-rich volcanic breccias geochemically similar to the Marion Island lavas. Lavas and breccias contain a suite of megacryst minerals and of small polymineralic xenoliths, in both of which kaersutite is a prominent constituent.The megacryst suite comprises large unzoned single grains of kaersutite, plagioclase, pyroxene, magnetite and ilmenite, all showing textural evidence of resorption/reaction with the basanitoid host. The megacrysts have a limited range of compositions except for the plagioclase which ranges from oligoclase to labradorite.The small (2 mm to ~ 3 cm) xenoliths are mostly two-pyroxene amphibole assemblages with or without olivine, magnetite, ilmenite, plagioclase and apatite. The xenoliths show some evidence of reaction with the basanitoid host and most have undergone recrystallization and/or localised decompression melting.Xenolith and megacryst assemblages are interpreted as being associated with the formation and partial crystallization of a hydrous basanitoid melt at depth.

Geochemistry of pyroxenitic and hornblenditic xenoliths in alkaline lamprophyres from the Spanish Central System

“…Orthopyroxene and olivine-poor mafic to ultra mafic xenoliths of gabbroic, homblenditic and py roxenitic types, carried by basaltic and basanitic melts are also common in other regions and have been described by many authors (Brooks and Platt, 1975;Wilshire and Sherv ais, 1975;Frey and Prinz, 1978 ;Dautria et al, 1987;Reid and Le Roex, 1988;Capedri et al ., 1989;Bondi et aI., 2002). They have been interpreted in most cases as segregates from crystallizing melts.…”

Pyroxenite xenoliths in basalts of the Roca Negra volcano, Catalonia

“…The amphibole was first classed with pargasite-ferrohastingsite [Tournon, 1968] based on a single analysis of the mineral, but its high TiO2 concentration (Table 7) provides a ground to attribute the amphibole of the Roca Negra xenoliths to kaersutite. As can be seen in Figure 6, this amphibole is compositionally identical with amphibole in xenoliths in oceanicisland basalts [Frisch and Schminke, 1970;Kogarko, 1990;Munoz et al, 1974;Reid and Le Roex, 1988;Sagredo, 1969] and such intraplate magmatic areas as the Tien Shan [Dobretsov and Dobretsova, 1975]. [Ionov and Hofmann, 1995;Ionov et al, 1984;Witt and Seck, 1989]; 3 -amphibole in pyroxenite xenoliths from the canary Islands, Frank Seamount in the Indian Ocean, the Cape Verde Islands in the Atlantic Ocean, Murcia, and the Tien Shan [Kogarko, 1990;Munoz et al, 1974;Reid and Le Roex, 1988;Sagredo, 1969]; 4amphibole in pyroxenite xenoliths from the Tien Shan [Dobretsov and Dobretsova, 1975].…”