Abstract
Vesicular interstitial glass in four kaersutite-bearing spinel–wehrlite xenoliths from Foster Crater, Antarctica has reacted with host olivine (Fo75–79) and clinopyroxene (Ca47 Mg45 Fe8) and contains a microphenocryst assemblage of spinel, olivine, and clinopyroxene together with later rhonite and plagioclase. Electron microprobe analyses of the glasses have low SiO2 (46–49 wt. per cent) and MgO (2.2–3.7) contents and high contents of alkalis, TiO2 (3.4–4.8), Al2O3 (18.1–20.6) and P2O5 (1.1–1.3). Olivine microphenocryst cores in glass are magnesian (up to Fo88) and must have precipitated from more primitive liquids; rim compositions are Fe-rich (Fo75) and in equilibrium with glass. Continuous core to rim zonation in the olivine microphenocrysts indicate that glass compositions have fractionated due to crystallization of the enclosed mineral assemblage. Mass balance addition calculations, using the compositions and proportions of the crystals in glass, produce melt compositions appropriate to primary alkali basaltic magmas. Glasses show light rare earth element (REE) enrichment relative to chondrites (Ce/YbN = 10.5) and, together with Ba, Rb, Cr, Hf, Ta, and Th are similar to many of the basanites from the Erebus Volcanic Province.

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