Carbonate assimilation at Merapi volcano, Java Indonesia: insights from crystal isotope stratigraphy

TY - JOUR

T1 - Carbonate assimilation at Merapi volcano, Java Indonesia

T2 - insights from crystal isotope stratigraphy

AU - Chadwick, J.P

AU - Troll, V.R

AU - Ginibre,, C.

AU - Morgan, D.

AU - Gertisser, R.

AU - Waight, Tod Earle

AU - Davidson, J.P.

PY - 2007

Y1 - 2007

N2 - Recent basaltic andesite lavas from Merapi volcano contain abundant, 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 surfaces 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 0.70568 to 0.70627.The upper end of this range is notably more radiogenic than the host basaltic andesite whole-rocks (0.70574). 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 metamorphosed volcanoclastic sediment and carbonate country rock (calc-silicate skarns) analysed here for petrographic textures, mineralogy, major element composition and Sr isotope composition. The xenoliths contain extremely calcic plagioclase (up to An100) and have whole-rock 87Sr/86Sr ratios of 0.70584 to 0.70786.The presence of these xenoliths and their mineralogy and geochemistry, coupled with the 87Sr/86Sr ratios observed in different zones of individual phenocrysts, indicate that magma-crust interaction at Merapi is potentially more significant than previously thought, as numerous crystal cores in the phenocrysts appear to be inherited from a metamorphosed sedimentary crustal source. This has potentially significant consequences for geochemical mass-balance calculations, volatile saturation and flux and eruptive behaviour at Merapi and similar island arc volcanic systems elsewhere.

AB - Recent basaltic andesite lavas from Merapi volcano contain abundant, 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 surfaces 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 0.70568 to 0.70627.The upper end of this range is notably more radiogenic than the host basaltic andesite whole-rocks (0.70574). 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 metamorphosed volcanoclastic sediment and carbonate country rock (calc-silicate skarns) analysed here for petrographic textures, mineralogy, major element composition and Sr isotope composition. The xenoliths contain extremely calcic plagioclase (up to An100) and have whole-rock 87Sr/86Sr ratios of 0.70584 to 0.70786.The presence of these xenoliths and their mineralogy and geochemistry, coupled with the 87Sr/86Sr ratios observed in different zones of individual phenocrysts, indicate that magma-crust interaction at Merapi is potentially more significant than previously thought, as numerous crystal cores in the phenocrysts appear to be inherited from a metamorphosed sedimentary crustal source. This has potentially significant consequences for geochemical mass-balance calculations, volatile saturation and flux and eruptive behaviour at Merapi and similar island arc volcanic systems elsewhere.

KW - Faculty of Science

KW - Indonesien

KW - isotoper

KW - assimilation

KW - calc-silicate

KW - xenolith

KW - Indonesia

KW - Merapi

KW - isotopes

U2 - 10.1093/petrology/egm038

DO - 10.1093/petrology/egm038

M3 - Journal article

SN - 0022-3530

VL - 48

SP - 1793

EP - 1812

JO - Journal of Petrology

JF - Journal of Petrology

ER -