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

Published online by Cambridge University Press:  05 July 2018

Arch M. Reid  and
Anton P. le Roex
Arch M. Reid
Affiliation:
Department of Geology, University of Cape Town, Rondebosch 7700, South Africa
Anton P. le Roex
Affiliation:
Department of Geology, University of Cape Town, Rondebosch 7700, South Africa
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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 (lat. 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.

Keywords

kaersutiteamphibolexenolithFunk SeamountIndian Ocean
Type
Mineralogy and Crystal Structures
Information
Mineralogical Magazine , Volume 52 , Issue 366 , June 1988 , pp. 359 - 370
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1988

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Footnotes

*

Present address: Department of Geosciences, University of Houston, Houston, Texas 77004, USA.

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