Clinopyroxene megacrysts from Marion Island, Antarctic Ocean : evidence for a late stage shallow origin

Inclusions of olivine, pyrrhotite, oxides, sulphides, and rounded inclusions with euhedral micro-crystals interpreted as former melt inclusions are observed. Olivine inclusions have variable compositions, ranging from primary Ti-poor crystals to Ti-rich crystals hosting secondary haematite crystals formed by hydrogenation.

The crystals contain voids, which are concentrated in the middle of each crystal, indicating that the initial crystal growth was skeletal. Subsequent crystallisation filled in the skeletal framework, creating the patchy zoning in the crystals. The Marion Island megacrysts are not homogenous, but the combination of crustal clinopyroxene compositions, primary and hydrogenated olivine, and the mode of eruption in scoria eruptions indicates that these crystals most likely formed in a shallow magma chamber.