Geochemistry and Petrogenesis of Silicic Magmas in the Intra-Oceanic Kermadec Arc
Geochemistry and Petrogenesis of Silicic Magmas in the Intra-Oceanic Kermadec Arc
The geochemistry of pyroclasts sampled from four volcanoes along the Kermadec arc in the SW Pacific is used to investigate the genesis of silicic magmas in a young (<2 Myr), archetypical intra-oceanic arc setting. Raoul, Macauley and Raoul SW volcanoes in the northern Kermadec arc, and Healy volcano in the southern Kermadec arc have all recently erupted dacitic to rhyolitic crystal-poor pumice. In addition to whole-rock analyses, we present a detailed study of mineral and glass chemistries to highlight the complex structure of the Kermadec magmatic systems. Major and trace element bulk-rock compositions mostly fall into relatively narrow compositional ranges, forming discrete groups by eruption for Raoul, and varying with relative crystal contents for Healy. In contrast, pumices from Macauley cover a wide range of compositions, between 66 and 72·5 wt % SiO2. At all four volcanoes the trace element patterns of pumice are subparallel to both those of previously erupted basalts and/or whole mafic blebs found both as discrete pyroclasts and as inclusions within pumices. Pb and Sr isotopic compositions have limited ranges within single volcanoes, but vary considerably along the arc, being more radiogenic in the southern volcanoes. Distinctive crystal populations and zonation patterns in pumices, mafic blebs and plutonic xenoliths indicate that many crystals did not grow in the evolved magmas, but are instead mixed from other sources including gabbros and hydrothermally altered tonalites. Such open-system mixing is ubiquitous at the four volcanoes. Oxygen isotope compositions of both phenocrysts (silicic origin) and xenocrysts or antecrysts (mafic origin) are typical for mantle-derived melts. Whole-rock, glass and mineral chemistries are consistent with evolved magmas being generated at each volcano through ?70–80% crystal fractionation of a basaltic parent. Our results are not consistent with silicic magma generation via crustal anatexis, as previously suggested for these Kermadec arc volcanoes. Although crystallization is the dominant process driving melt evolution in the Kermadec volcanoes, we show that the magmatic systems are open to contributions from both newly arriving melts and wholly crystalline plutonic bodies. Such processes occur in variable proportions between magma batches, and are largely reflected in small-scale chemical variations between eruption units.
fractional crystallization, Kermadec, magma mixing, oceanic arc, anatexis
351 -391
Barker, S.J.
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Wilson, C.J.N.
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Baker, J.A.
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Millet, M-A.
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Rotella, M.D.
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Wright, I.C.
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Wysoczanski, R.J.
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2013
Barker, S.J.
8fd2a509-2489-4d48-be0c-74ae52e34a08
Wilson, C.J.N.
8bb8f379-47dd-4db4-b095-e6745157ea82
Baker, J.A.
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Millet, M-A.
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Rotella, M.D.
1caaca11-c01e-49fc-9047-630aff98b47b
Wright, I.C.
be2a8931-3932-4f1e-b387-43e3652bf3fc
Wysoczanski, R.J.
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Barker, S.J., Wilson, C.J.N., Baker, J.A., Millet, M-A., Rotella, M.D., Wright, I.C. and Wysoczanski, R.J.
(2013)
Geochemistry and Petrogenesis of Silicic Magmas in the Intra-Oceanic Kermadec Arc.
Journal of Petrology, 54 (2), .
(doi:10.1093/petrology/egs071).
Abstract
The geochemistry of pyroclasts sampled from four volcanoes along the Kermadec arc in the SW Pacific is used to investigate the genesis of silicic magmas in a young (<2 Myr), archetypical intra-oceanic arc setting. Raoul, Macauley and Raoul SW volcanoes in the northern Kermadec arc, and Healy volcano in the southern Kermadec arc have all recently erupted dacitic to rhyolitic crystal-poor pumice. In addition to whole-rock analyses, we present a detailed study of mineral and glass chemistries to highlight the complex structure of the Kermadec magmatic systems. Major and trace element bulk-rock compositions mostly fall into relatively narrow compositional ranges, forming discrete groups by eruption for Raoul, and varying with relative crystal contents for Healy. In contrast, pumices from Macauley cover a wide range of compositions, between 66 and 72·5 wt % SiO2. At all four volcanoes the trace element patterns of pumice are subparallel to both those of previously erupted basalts and/or whole mafic blebs found both as discrete pyroclasts and as inclusions within pumices. Pb and Sr isotopic compositions have limited ranges within single volcanoes, but vary considerably along the arc, being more radiogenic in the southern volcanoes. Distinctive crystal populations and zonation patterns in pumices, mafic blebs and plutonic xenoliths indicate that many crystals did not grow in the evolved magmas, but are instead mixed from other sources including gabbros and hydrothermally altered tonalites. Such open-system mixing is ubiquitous at the four volcanoes. Oxygen isotope compositions of both phenocrysts (silicic origin) and xenocrysts or antecrysts (mafic origin) are typical for mantle-derived melts. Whole-rock, glass and mineral chemistries are consistent with evolved magmas being generated at each volcano through ?70–80% crystal fractionation of a basaltic parent. Our results are not consistent with silicic magma generation via crustal anatexis, as previously suggested for these Kermadec arc volcanoes. Although crystallization is the dominant process driving melt evolution in the Kermadec volcanoes, we show that the magmatic systems are open to contributions from both newly arriving melts and wholly crystalline plutonic bodies. Such processes occur in variable proportions between magma batches, and are largely reflected in small-scale chemical variations between eruption units.
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Barker et al JPet 54 351 2013.pdf
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e-pub ahead of print date: 11 November 2012
Published date: 2013
Keywords:
fractional crystallization, Kermadec, magma mixing, oceanic arc, anatexis
Organisations:
Marine Geoscience
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Local EPrints ID: 345167
URI: http://eprints.soton.ac.uk/id/eprint/345167
ISSN: 0022-3530
PURE UUID: 21349d8f-0301-4cb9-919c-43833ade7196
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Date deposited: 12 Nov 2012 09:52
Last modified: 14 Mar 2024 12:21
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Author:
S.J. Barker
Author:
C.J.N. Wilson
Author:
J.A. Baker
Author:
M-A. Millet
Author:
M.D. Rotella
Author:
I.C. Wright
Author:
R.J. Wysoczanski
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