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Petrological and experimental evidence for differentiation of water-rich magmas beneath St. Kitts, Lesser Antilles

Blundy, J.D.; Melekhova, E; Martin, Rita; Arculus, Richard; Pichavant, Michel

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St. Kitts lies in the northern Lesser Antilles, a subduction-related intraoceanic volcanic arc known for its magmatic diversity and unusually abundant cognate xenoliths. We combine the geochemistry of xenoliths, melt inclusions and lavas with high pressure–temperature experiments to explore magma differentiation processes beneath St. Kitts. Lavas range from basalt to rhyolite, with predominant andesites and basaltic andesites. Xenoliths, dominated by calcic plagioclase and amphibole, typically...[Show more]

dc.contributor.authorBlundy, J.D.
dc.contributor.authorMelekhova, E
dc.contributor.authorMartin, Rita
dc.contributor.authorArculus, Richard
dc.contributor.authorPichavant, Michel
dc.date.accessioned2021-08-30T03:34:28Z
dc.date.available2021-08-30T03:34:28Z
dc.identifier.issn0010-7999
dc.identifier.urihttp://hdl.handle.net/1885/245920
dc.description.abstractSt. Kitts lies in the northern Lesser Antilles, a subduction-related intraoceanic volcanic arc known for its magmatic diversity and unusually abundant cognate xenoliths. We combine the geochemistry of xenoliths, melt inclusions and lavas with high pressure–temperature experiments to explore magma differentiation processes beneath St. Kitts. Lavas range from basalt to rhyolite, with predominant andesites and basaltic andesites. Xenoliths, dominated by calcic plagioclase and amphibole, typically in reaction relationship with pyroxenes and olivine, can be divided into plutonic and cumulate varieties based on mineral textures and compositions. Cumulate varieties, formed primarily by the accumulation of liquidus phases, comprise ensembles that represent instantaneous solid compositions from one or more magma batches; plutonic varieties have mineralogy and textures consistent with protracted solidification of magmatic mush. Mineral chemistry in lavas and xenoliths is subtly different. For example, plagioclase with unusually high anorthite content (An≤100) occurs in some plutonic xenoliths, whereas the most calcic plagioclase in cumulate xenoliths and lavas are An97 and An95, respectively. Fluid-saturated, equilibrium crystallisation experiments were performed on a St. Kitts basaltic andesite, with three different fluid compositions (XH2O = 1.0, 0.66 and 0.33) at 2.4 kbar, 950–1025 °C, and fO2 = NNO − 0.6 to NNO + 1.2 log units. Experiments reproduce lava liquid lines of descent and many xenolith assemblages, but fail to match xenolith and lava phenocryst mineral compositions, notably the very An-rich plagioclase. The strong positive correlation between experimentally determined plagioclase-melt KdCa–Na and dissolved H2O in the melt, together with the occurrence of Al-rich mafic lavas, suggests that parental magmas were water-rich (> 9 wt% H2O) basaltic andesites that crystallised over a wide pressure range (1.5–6 kbar). Comparison of experimental and natural (lava, xenolith) mafic mineral composition reveals that whereas olivine in lavas is predominantly primocrysts precipitated at low-pressure, pyroxenes and spinel are predominantly xenocrysts formed by disaggregation of plutonic mushes. Overall, St. Kitts xenoliths and lavas testify to mid-crustal differentiation of low-MgO basalt and basaltic andesite magmas within a trans-crustal, magmatic mush system. Lower crustal ultramafic cumulates that relate parental low-MgO basalts to primary, mantle -derived melts are absent on St. Kitts.
dc.description.sponsorshipThis research was supported by grants from ERC (“CRITMAG”) and NERC (NE/N001966/1). JB acknowledges a Wolfson Research Merit Award from the Royal Society.
dc.format.mimetypeapplication/pdf
dc.language.isoen_AU
dc.publisherSpringer
dc.rights© The Author(s) 2017.
dc.rights.urihttp://creativecommons.org/licenses/by/4.0/
dc.sourceContributions to Mineralogy and Petrology
dc.subjectXenolith
dc.subjectCumulates
dc.subjectHigh-An plagioclase
dc.subjectDiferentiation of basaltic andesite
dc.subjectExperiments
dc.subject‘Magma mush’
dc.titlePetrological and experimental evidence for differentiation of water-rich magmas beneath St. Kitts, Lesser Antilles
dc.typeJournal article
local.description.notesImported from ARIES
local.identifier.citationvolume172
dc.date.issued2017
local.identifier.absfor040201 - Exploration Geochemistry
local.identifier.absfor040304 - Igneous and Metamorphic Petrology
local.identifier.ariespublicationa383154xPUB8920
local.publisher.urlhttps://link.springer.com/
local.type.statusPublished Version
local.contributor.affiliationBlundy, J.D., University of Bristol
local.contributor.affiliationMelekhova, E, University of Bristol
local.contributor.affiliationMartin, Rita, University of Bristol
local.contributor.affiliationArculus, Richard, College of Science, ANU
local.contributor.affiliationPichavant, Michel, ISTO
local.bibliographicCitation.issue98
local.bibliographicCitation.startpage1
local.bibliographicCitation.lastpage32
local.identifier.doi10.1007/s00410-017-1416-3
dc.date.updated2020-11-23T10:56:05Z
local.identifier.scopusID2-s2.0-85034443448
dcterms.accessRightsOpen Access
dc.provenanceThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.
dc.rights.licenseCreative Commons Attribution 4.0 International License
CollectionsANU Research Publications

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