Isotopic Compositions of Plagioclase From Plutonic Xenoliths Reveal Crustal Assimilation Below Martinique, Lesser Antilles Arc

The chemical and isotopic compositions of volcanic arc lavas often show evidence for involvement of a sedimentary component during magma genesis. Determining where this sedimentary component is added to arc magmas is of vital importance for constraining the extent to which sediments and volatiles ar...

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Main Authors: J. R. Brown, G. F. Cooper, G. M. Nowell, C. G. Macpherson, I. Neill, J. Prytulak
Format: Article
Language:English
Published: Frontiers Media S.A. 2021-05-01
Series:Frontiers in Earth Science
Subjects:
Online Access:https://www.frontiersin.org/articles/10.3389/feart.2021.682583/full
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author J. R. Brown
G. F. Cooper
G. M. Nowell
C. G. Macpherson
I. Neill
J. Prytulak
author_facet J. R. Brown
G. F. Cooper
G. M. Nowell
C. G. Macpherson
I. Neill
J. Prytulak
author_sort J. R. Brown
collection DOAJ
description The chemical and isotopic compositions of volcanic arc lavas often show evidence for involvement of a sedimentary component during magma genesis. Determining where this sedimentary component is added to arc magmas is of vital importance for constraining the extent to which sediments and volatiles are recycled at subduction zones. Lavas from Martinique in the Lesser Antilles arc have wide ranging isotopic compositions extending to highly radiogenic values (e.g. 87/Sr/86Sr up to ∼0.710) that could, in principle, be explained by sediment addition to the mantle source or by crustal assimilation in the upper plate. We use Sr isotopic compositions of plagioclase from Martinique plutonic xenoliths to provide evidence supporting the crustal assimilation hypothesis. Plagioclase from plutonic xenoliths formed in the mid-crust (∼12 km) show a restricted range of unradiogenic Sr isotope ratios (87Sr/86Sr = 0.7041–0.7042) whereas plagioclase from upper crustal plutonic xenoliths (∼6 km) show greater intra-sample variation and more radiogenic Sr isotopic compositions up to 87Sr/86Sr = 0.7047. This trend is also observed in plutonic xenolith whole rock 87Sr/86Sr. Combined, these results indicate that the range of Sr isotope compositions becomes larger and more radiogenic in Martinique magmas as a result of sediment assimilation at shallow crustal levels. This is supported by Assimilation-Fractional Crystallization modeling, which shows that assimilation of chemically and isotopically heterogenous crustal sediments can produce the isotopic variation in Martinique plutonic xenoliths and lavas. Our results highlight the importance of constraining crustal contributions from the upper plate before using arc lava geochemistry to quantify sediment and volatile recycling at subduction zones and assessing potential heterogeneity of arc mantle sources.
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spelling doaj.art-9eb93f833e1c4962b68bcc62e6fa27752022-12-21T22:06:33ZengFrontiers Media S.A.Frontiers in Earth Science2296-64632021-05-01910.3389/feart.2021.682583682583Isotopic Compositions of Plagioclase From Plutonic Xenoliths Reveal Crustal Assimilation Below Martinique, Lesser Antilles ArcJ. R. Brown0G. F. Cooper1G. M. Nowell2C. G. Macpherson3I. Neill4J. Prytulak5Department of Earth Sciences, Durham University, Durham, United KingdomSchool of Earth and Ocean Sciences, Cardiff University, Cardiff, United KingdomDepartment of Earth Sciences, Durham University, Durham, United KingdomDepartment of Earth Sciences, Durham University, Durham, United KingdomSchool of Geographical and Earth Sciences, University of Glasgow, Glasgow, United KingdomDepartment of Earth Sciences, Durham University, Durham, United KingdomThe chemical and isotopic compositions of volcanic arc lavas often show evidence for involvement of a sedimentary component during magma genesis. Determining where this sedimentary component is added to arc magmas is of vital importance for constraining the extent to which sediments and volatiles are recycled at subduction zones. Lavas from Martinique in the Lesser Antilles arc have wide ranging isotopic compositions extending to highly radiogenic values (e.g. 87/Sr/86Sr up to ∼0.710) that could, in principle, be explained by sediment addition to the mantle source or by crustal assimilation in the upper plate. We use Sr isotopic compositions of plagioclase from Martinique plutonic xenoliths to provide evidence supporting the crustal assimilation hypothesis. Plagioclase from plutonic xenoliths formed in the mid-crust (∼12 km) show a restricted range of unradiogenic Sr isotope ratios (87Sr/86Sr = 0.7041–0.7042) whereas plagioclase from upper crustal plutonic xenoliths (∼6 km) show greater intra-sample variation and more radiogenic Sr isotopic compositions up to 87Sr/86Sr = 0.7047. This trend is also observed in plutonic xenolith whole rock 87Sr/86Sr. Combined, these results indicate that the range of Sr isotope compositions becomes larger and more radiogenic in Martinique magmas as a result of sediment assimilation at shallow crustal levels. This is supported by Assimilation-Fractional Crystallization modeling, which shows that assimilation of chemically and isotopically heterogenous crustal sediments can produce the isotopic variation in Martinique plutonic xenoliths and lavas. Our results highlight the importance of constraining crustal contributions from the upper plate before using arc lava geochemistry to quantify sediment and volatile recycling at subduction zones and assessing potential heterogeneity of arc mantle sources.https://www.frontiersin.org/articles/10.3389/feart.2021.682583/fullcrustal sediment assimilationplutonic xenolithsstrontium isotopeslesser antilles arcplagioclasemartinique
spellingShingle J. R. Brown
G. F. Cooper
G. M. Nowell
C. G. Macpherson
I. Neill
J. Prytulak
Isotopic Compositions of Plagioclase From Plutonic Xenoliths Reveal Crustal Assimilation Below Martinique, Lesser Antilles Arc
Frontiers in Earth Science
crustal sediment assimilation
plutonic xenoliths
strontium isotopes
lesser antilles arc
plagioclase
martinique
title Isotopic Compositions of Plagioclase From Plutonic Xenoliths Reveal Crustal Assimilation Below Martinique, Lesser Antilles Arc
title_full Isotopic Compositions of Plagioclase From Plutonic Xenoliths Reveal Crustal Assimilation Below Martinique, Lesser Antilles Arc
title_fullStr Isotopic Compositions of Plagioclase From Plutonic Xenoliths Reveal Crustal Assimilation Below Martinique, Lesser Antilles Arc
title_full_unstemmed Isotopic Compositions of Plagioclase From Plutonic Xenoliths Reveal Crustal Assimilation Below Martinique, Lesser Antilles Arc
title_short Isotopic Compositions of Plagioclase From Plutonic Xenoliths Reveal Crustal Assimilation Below Martinique, Lesser Antilles Arc
title_sort isotopic compositions of plagioclase from plutonic xenoliths reveal crustal assimilation below martinique lesser antilles arc
topic crustal sediment assimilation
plutonic xenoliths
strontium isotopes
lesser antilles arc
plagioclase
martinique
url https://www.frontiersin.org/articles/10.3389/feart.2021.682583/full
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