Carbonate Assimilation at MerapiVolcano, Java, Indonesia: Insights from Crystal Isotope Stratigraphy

Recent basaltic andesite lavas from Merapi volcano contain abun-dant, complexly zoned, plagioclase phenocrysts, analysed here for their petrographic textures, major element composition and Sr isotope composition. Anorthite (An) content in individual crystals can vary by as much as 55 mol % (An40^95) across internal resorption sur-faces with a negative correlation between high An mol % (470), MgO wt % and FeO wt%. In situ Sr isotope analyses of zoned plagioclase phenocrysts show that the 87Sr/86Sr ratios of individual zones range from 070568 to 070627.The upper end of this range is notably more radiogenic than the host basaltic andesite whole-rocks (5070574). Crystal zones with the highest An content have the highest 87Sr/86Sr values, requiring a source or melt with elevated radiogenic Sr, rich in Ca and with lower Mg and Fe. Recent Merapi eruptive rocks contain abundant xenoliths, including meta-morphosed volcanoclastic sediment and carbonate country roc