|
|||||
|
|
Carbonate Assimilation at Merapi Volcano, Java, Indonesia: Insights from Crystal Isotope Stratigraphy |
|
| Authors: | Chadwick Jane P; Troll Valentin R; Ginibre Catherine; Morgan Daniel; Gertisser Ralf; Waight Tod E; Davidson Jon P |
| Institution: | 1Department of Geology, the University of Dublin, Trinity College, Dublin 2, Ireland 2Department of Earth Sciences, University of Durham, South Road, Durham DH1 3LE, UK 3Department of Mineralogy, University of Geneva, Rue Des Maraîchers, 13 CH-1205, Geneva, Switzerland 4School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UK 5School of Physical and Geographical Sciences, Keele University, Keele ST5 5BG, UK 6Geological Institute, Øster Voldgade 10, 1350 Copenhagen K, Denmark |
| Abstract: | Recent basaltic andesite lavas from Merapi volcano contain abundant,complexly zoned, plagioclase phenocrysts, analysed here fortheir petrographic textures, major element composition and Srisotope composition. Anorthite (An) content in individual crystalscan vary by as much as 55 mol% (An40–95) across internalresorption surfaces with a negative correlation between highAn mol% (>70), MgO wt% and FeO wt%. In situ Sr isotope analysesof zoned plagioclase phenocrysts show that the 87Sr/86Sr ratiosof individual zones range from 0·70568 to 0·70627.The upper end of this range is notably more radiogenic thanthe host basaltic andesite whole-rocks (< 0·70574).Crystal zones with the highest An content have the highest 87Sr/86Srvalues, requiring a source or melt with elevated radiogenicSr, rich in Ca and with lower Mg and Fe. Recent Merapi eruptiverocks contain abundant xenoliths, including metamorphosed volcanoclasticsediment and carbonate country rock (calc-silicate skarns) analysedhere for petrographic textures, mineralogy, major element compositionand Sr isotope composition. The xenoliths contain extremelycalcic plagioclase (up to An100) and have whole-rock 87Sr/86Srratios of 0·70584 to 0·70786. The presence ofthese xenoliths and their mineralogy and geochemistry, coupledwith the 87Sr/86Sr ratios observed in different zones of individualphenocrysts, indicate that magma–crust interaction atMerapi is potentially more significant than previously thought,as numerous crystal cores in the phenocrysts appear to be inheritedfrom a metamorphosed sedimentary crustal source. This has potentiallysignificant consequences for geochemical mass-balance calculations,volatile saturation and flux and eruptive behaviour at Merapiand similar island arc volcanic systems elsewhere. KEY WORDS: assimilation; isotopes; Merapi; xenolith; calc-silicate |
| Keywords: | : assimilation isotopes Merapi xenolith calc-silicate |
| 本文献已被 Oxford 等数据库收录！ | |