Shallow-level decompression crystallisation and deep magma supply at Shiveluch Volcano

Humphreys, M. C. S. and Blundy, J. D. and Sparks, R. S. J. (2008) Shallow-level decompression crystallisation and deep magma supply at Shiveluch Volcano. Contributions to Mineralogy and Petrology, 155 (1). pp. 45-61. ISSN 0010-7999 (Print) 1432-0967 (Online) DOI 10.1007/s00410-007-0223-7

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Abstract

Recent petrological studies indicate that some crustal magma chambers may be built up slowly by the intermittent ascent and amalgamation of small packets of magma generated in a deep-seated source region. Despite having little effect on whole-rock compositions, this process should be detectable as variable melt trace element composition, preserved as melt inclusions trapped in phenocrysts. We studied trace element and H2O contents of plagioclase- and hornblende-hosted melt inclusions from andesite lavas and pumices of Shiveluch Volcano, Kamchatka. Melt inclusions are significantly more evolved than the whole rocks, indicating that the whole rocks contain a significant proportion of recycled foreign material. H2O concentrations indicate trapping at a wide range of pressures, consistent with shallow decompression-driven crystallisation. The variation of trace element concentrations indicates up to ∼30% decompression crystallisation, which accounts for crystallisation of the groundmass and rims on phenocrysts. Trace element scatter could be explained by episodic stalling during shallow magma ascent, allowing incompatible element concentrations to increase during isobaric crystallisation. Enrichment of Li at intermediate pH2O reflects influx and condensation of metal-rich vapours. A set of “exotic melts”, identified by their anomalous incompatible trace element characteristics, indicate variable source chemistry. This is consistent with evolution of individual magma batches with small differences in trace element chemistry, and intermittent ascent of magma pulses.

Item Type: Article
Uncontrolled Keywords: 2007 AREP 2007 P IA55
Subjects: 05 - Petrology - Igneous, Metamorphic and Volcanic Studies
Divisions: 05 - Petrology - Igneous, Metamorphic and Volcanic Studies
Journal or Publication Title: Contributions to Mineralogy and Petrology
Volume: 155
Page Range: pp. 45-61
Identification Number: 10.1007/s00410-007-0223-7
Depositing User: Sarah Humbert
Date Deposited: 16 Feb 2009 13:02
Last Modified: 23 Jul 2013 10:07
URI: http://eprints.esc.cam.ac.uk/id/eprint/417

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