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dc.contributor.authorNeave, Daviden
dc.contributor.authorMaclennan, Johnen
dc.contributor.authorHartley, Margaret Een
dc.contributor.authorEdmonds, Marieen
dc.contributor.authorThordarson, Thorvalduren
dc.date.accessioned2014-10-17T11:09:40Z
dc.date.available2014-10-17T11:09:40Z
dc.date.issued2014-10-31en
dc.identifier.citationJournal of Petrology 55 (12): 2311-2346. doi: 10.1093/petrology/egu058en
dc.identifier.issn0022-3530
dc.identifier.urihttps://www.repository.cam.ac.uk/handle/1810/246196
dc.description.abstractMagma mixing and crystal mush disaggregation are important processes in basaltic magma reservoirs. We carried out a detailed petrological and geochemical study on a highly plagioclase-phyric eruption within the Eastern Volcanic Zone of Iceland – the Skuggafjöll eruption – in order to investigate crystal storage and transport processes within a single magmatic system. Crystal content and phase proportions vary between samples: the least phyric samples have phase proportions similar to the low pressure, 3-phase gabbro eutectic (plg:cpx:ol ~ 11:6:3), whereas highly phyric samples are strongly enriched in plagioclase (plg:cpx:ol ~ 8:1:1). Statistically significant geochemical variability in 28 whole-rock samples collected across the eruption can be accounted for by variable accumulation of a troctolitic assemblage containing plagioclase and olivine in an approximately 9:1 ratio. Two macrocryst assemblages are defined using compositional and textural information recorded in QEMSCAN® images: a primitive assemblage of high-anorthite plagioclase (An>83) and high-forsterite olivine (Fo>84), and an evolved assemblage of low-anorthite plagioclase (An<79), low forsterite olivine (Fo<82) and clinopyroxene (Mg# ~ 82). Plagioclase and olivine have strongly bimodal composition distributions whereas the composition distribution of clinopyroxene is unimodal. The mean trace element composition of melt inclusions hosted within high-forsterite olivine and high-anorthite plagioclase macrocrysts is the same (mean Ce/Y ~ 0.47–0.48), confirming that both primitive macrocryst phases crystallised from the same distribution of melts. Clinopyroxene macrocrysts and matrix glasses are in Ce/Yb equilibrium with each other, indicating that the evolved assemblage crystallised from melts with a more incompatible trace element-enriched composition (mean Ce/Y ~ 0.65–71) than the primitive assemblage. Variability in whole-rock, macrocryst and melt inclusion compositions suggests that the Skuggafjöll magma experienced two stages of crystallisation. Primitive macrocrysts crystallised first from incompatible trace element-depleted melts within a shallow crustal magma reservoir. These primitive macrocrysts were subsequently stored in crystal mushes that ultimately disaggregated into an evolved and incompatible trace element-enriched magma from which the evolved assemblage crystallised. On average, ~17% of the erupted magma at Skuggafjöll is composed of accumulated macrocrysts entrained from crystal mushes. The timescale between mush disaggregation and eruption, during which crystal accumulation occurred, was short – of the order of years – according to simple diffusion calculations. Striking petrological similarities between Skuggafjöll and other highly phyric eruptions both in Iceland and along mid-ocean ridges indicate that crystal accumulation by mush disaggregation is likely to be an important mechanism for generating highly phyric magmas in basaltic plumbing systems.
dc.languageEnglishen
dc.language.isoenen
dc.publisherOUP
dc.rightsAttribution 2.0 UK: England & Wales
dc.rights.urihttp://creativecommons.org/licenses/by/2.0/uk/
dc.titleCrystal storage and transfer in basaltic systems: the Skuggafjöll eruption, Icelanden
dc.typeArticle
dc.description.versionThis is the final version. It was first published by OUP at http://petrology.oxfordjournals.org/content/55/12/2311.en
prism.endingPage2346
prism.publicationDate2014en
prism.publicationNameJournal of Petrologyen
prism.startingPage2311
prism.volume55en
dc.rioxxterms.funderNatural Environment Research Council
dc.rioxxterms.projectidNE/1528277/1 and IMF484/0513
rioxxterms.versionofrecord10.1093/petrology/egu058en
rioxxterms.licenseref.urihttp://www.rioxx.net/licenses/all-rights-reserveden
rioxxterms.licenseref.startdate2014-10-31en
dc.contributor.orcidMaclennan, John [0000-0001-6857-9600]
dc.contributor.orcidEdmonds, Marie [0000-0003-1243-137X]
dc.identifier.eissn1460-2415
rioxxterms.typeJournal Article/Reviewen
pubs.funder-project-idNERC (NE/I012508/1)


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Attribution 2.0 UK: England & Wales
Except where otherwise noted, this item's licence is described as Attribution 2.0 UK: England & Wales