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Textural history of recent basaltic-andesites and plutonic inclusions from Merapi volcano
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
2013 (English)In: Contributions to Mineralogy and Petrology, ISSN 0010-7999, E-ISSN 1432-0967, Vol. 166, no 1, 43-63 p.Article in journal (Refereed) Published
Abstract [en]

Mt. Merapi in Central Java is one of the most active stratovolcanoes on Earth and is underlain by a multistage plumbing system. Crystal size distribution analyses (CSD) were carried out on recent Merapi basaltic-andesites and co-eruptive magmatic and plutonic inclusions to characterise the crystallisation processes that operate during storage and ascent and to obtain information on respective time scales. The basaltic-andesites exhibit log-linear, kinked-upwards CSD curves for plagioclase and clinopyroxene that can be separated into two main textural populations. Large plagioclase phenocrysts (a parts per thousand yen1.6 mm) make up one population, but correspond to crystals with variable geochemical composition and reflect a period of crystal growth at deep to mid-crustal levels. This population was subsequently influenced by crystal accumulation and the onset of crustal assimilation, including the incorporation of high-Ca skarn-derived xenocrysts. Textural re-equilibration is required for these crystals to form a single population in CSD. A second episode of crystal growth at shallower levels is represented by chemically homogenous plagioclase crystals < 1.6 mm in size. Crustal assimilation is indicated by, for example, oxygen isotopes and based on the CSD data, crystallisation combined with contamination is likely semi-continuous in these upper crustal storage chambers. The CSD data observed in the basaltic-andesite samples are remarkably consistent and require a large-volume steady state magmatic system beneath Merapi in which late textural equilibration plays a significant role. Plagioclase CSDs of co-eruptive magmatic and plutonic inclusions may contain a third crystal population (< 1 mm) not found in the lavas. This third population has probably formed from enhanced degassing of portions of basaltic-andesite magma at shallow crustal levels which resulted in increased crystallinity and basaltic-andesite mush inclusions. A suite of coarse plutonic inclusions is also present that reflects crystallisation and accumulation of crystals in the deep Merapi plumbing system, as deduced from CSD patterns and mineral assemblages.

Place, publisher, year, edition, pages
2013. Vol. 166, no 1, 43-63 p.
Keyword [en]
Basaltic-andesite, Crystal size distribution, Plutonic inclusions, Volcanic plumbing system, Merapi volcano
National Category
Earth and Related Environmental Sciences Geology
Research subject
Earth Science with specialization in Mineral Chemistry, Petrology and Tectonics
URN: urn:nbn:se:uu:diva-204782DOI: 10.1007/s00410-013-0864-7ISI: 000320655900003OAI: oai:DiVA.org:uu-204782DiVA: diva2:641108
Available from: 2013-08-15 Created: 2013-08-12 Last updated: 2013-12-18Bibliographically approved

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Troll, Valentin R.
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