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

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 di...

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Autores principales: Melekhova, Elena, Blundy, Jon, Martin, Rita, Arculus, Richard, Pichavant, Michel
Formato: Online Artículo Texto
Lenguaje:English
Publicado: Springer Berlin Heidelberg 2017
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6959387/
https://www.ncbi.nlm.nih.gov/pubmed/32009663
http://dx.doi.org/10.1007/s00410-017-1416-3
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author Melekhova, Elena
Blundy, Jon
Martin, Rita
Arculus, Richard
Pichavant, Michel
author_facet Melekhova, Elena
Blundy, Jon
Martin, Rita
Arculus, Richard
Pichavant, Michel
author_sort Melekhova, Elena
collection PubMed
description 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 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 An(97) and An(95), respectively. Fluid-saturated, equilibrium crystallisation experiments were performed on a St. Kitts basaltic andesite, with three different fluid compositions (XH(2)O = 1.0, 0.66 and 0.33) at 2.4 kbar, 950–1025 °C, and fO(2) = 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 Kd(Ca–Na) and dissolved H(2)O in the melt, together with the occurrence of Al-rich mafic lavas, suggests that parental magmas were water-rich (> 9 wt% H(2)O) 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. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1007/s00410-017-1416-3) contains supplementary material, which is available to authorized users.
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spelling pubmed-69593872020-01-29 Petrological and experimental evidence for differentiation of water-rich magmas beneath St. Kitts, Lesser Antilles Melekhova, Elena Blundy, Jon Martin, Rita Arculus, Richard Pichavant, Michel Contrib Mineral Petrol Original Paper 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 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 An(97) and An(95), respectively. Fluid-saturated, equilibrium crystallisation experiments were performed on a St. Kitts basaltic andesite, with three different fluid compositions (XH(2)O = 1.0, 0.66 and 0.33) at 2.4 kbar, 950–1025 °C, and fO(2) = 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 Kd(Ca–Na) and dissolved H(2)O in the melt, together with the occurrence of Al-rich mafic lavas, suggests that parental magmas were water-rich (> 9 wt% H(2)O) 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. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1007/s00410-017-1416-3) contains supplementary material, which is available to authorized users. Springer Berlin Heidelberg 2017-11-10 2017 /pmc/articles/PMC6959387/ /pubmed/32009663 http://dx.doi.org/10.1007/s00410-017-1416-3 Text en © The Author(s) 2017 Open AccessThis 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.
spellingShingle Original Paper
Melekhova, Elena
Blundy, Jon
Martin, Rita
Arculus, Richard
Pichavant, Michel
Petrological and experimental evidence for differentiation of water-rich magmas beneath St. Kitts, Lesser Antilles
title Petrological and experimental evidence for differentiation of water-rich magmas beneath St. Kitts, Lesser Antilles
title_full Petrological and experimental evidence for differentiation of water-rich magmas beneath St. Kitts, Lesser Antilles
title_fullStr Petrological and experimental evidence for differentiation of water-rich magmas beneath St. Kitts, Lesser Antilles
title_full_unstemmed Petrological and experimental evidence for differentiation of water-rich magmas beneath St. Kitts, Lesser Antilles
title_short Petrological and experimental evidence for differentiation of water-rich magmas beneath St. Kitts, Lesser Antilles
title_sort petrological and experimental evidence for differentiation of water-rich magmas beneath st. kitts, lesser antilles
topic Original Paper
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6959387/
https://www.ncbi.nlm.nih.gov/pubmed/32009663
http://dx.doi.org/10.1007/s00410-017-1416-3
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