Mantle metasomatism and rapid ascent of slab components beneath island arcs: Evidence from 238U-230Th-226Ra disequilibria of Miyakejima volcano, Izu arc, Japan

Tetsuya Yokoyama, Katsura Kobayashi, Takeshi Kuritani, Eizou Nakamura

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48 Citations (Scopus)

Abstract

238U-230Th-226Ra systematics in lavas from Miyakejima volcano, Japan, are presented to estimate the timescale of magmatic processes beneath an island arc. Miyakejima volcano has four recent eruptive stages (Stages 1-4) starting >7000 BP. 238U-230Th-226Ra disequilibria observed in lavas with large 238U and 226Ra excesses imply metasomatism of depleted mantle by fluid-related processes. This metasomatism is also suggested by trace element and Sr-Nd-Pb isotopic systematics in the same lavas. In the equiline diagram, the trends for two magmatic stages (Stages 1 and 2) are regarded as two different isochrons with a common initial (230Th/232Th) ratio, although the trend for Stages 3 and 4 is a magma mixing line. Our model calculations show that slab-derived fluids can deliver some Th and a very rapid ascent time of the slab components in the mantle wedge (<7 kyr) is inferred. This rapid ascent can be explained by nearly instantaneous material transport in the mantle wedge by a hydrofracture model for fluid and a channel flow model for melt. Such a timescale estimate is not increased even if melting processes that enhance 226Ra are taken into account. The age difference in the equiline diagram corresponds to the interval of individual fluid-release events (13 kyr between Stages 1 and 2, and 5 kyr between Stages 2 and 3 . Thus fluid release from the slab and subsequent magma generation occur as episodic events on a several-kiloyear timescale.

Original languageEnglish
JournalJournal of Geophysical Research B: Solid Earth
Volume108
Issue number7
Publication statusPublished - Jul 10 2003

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Volcanoes
island arcs
ascent
metasomatism
disequilibrium
volcanoes
island arc
slab
Japan
Earth mantle
slabs
volcano
arcs
mantle
Fluids
fluid
fluids
timescale
wedges
magma

Keywords

  • Miyakejima volcano
  • Slab dehydration
  • Timescales
  • U-series disequilibria

ASJC Scopus subject areas

  • Earth and Planetary Sciences (miscellaneous)
  • Atmospheric Science
  • Geochemistry and Petrology
  • Geophysics
  • Oceanography
  • Space and Planetary Science
  • Astronomy and Astrophysics

Cite this

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title = "Mantle metasomatism and rapid ascent of slab components beneath island arcs: Evidence from 238U-230Th-226Ra disequilibria of Miyakejima volcano, Izu arc, Japan",
abstract = "238U-230Th-226Ra systematics in lavas from Miyakejima volcano, Japan, are presented to estimate the timescale of magmatic processes beneath an island arc. Miyakejima volcano has four recent eruptive stages (Stages 1-4) starting >7000 BP. 238U-230Th-226Ra disequilibria observed in lavas with large 238U and 226Ra excesses imply metasomatism of depleted mantle by fluid-related processes. This metasomatism is also suggested by trace element and Sr-Nd-Pb isotopic systematics in the same lavas. In the equiline diagram, the trends for two magmatic stages (Stages 1 and 2) are regarded as two different isochrons with a common initial (230Th/232Th) ratio, although the trend for Stages 3 and 4 is a magma mixing line. Our model calculations show that slab-derived fluids can deliver some Th and a very rapid ascent time of the slab components in the mantle wedge (<7 kyr) is inferred. This rapid ascent can be explained by nearly instantaneous material transport in the mantle wedge by a hydrofracture model for fluid and a channel flow model for melt. Such a timescale estimate is not increased even if melting processes that enhance 226Ra are taken into account. The age difference in the equiline diagram corresponds to the interval of individual fluid-release events (13 kyr between Stages 1 and 2, and 5 kyr between Stages 2 and 3 . Thus fluid release from the slab and subsequent magma generation occur as episodic events on a several-kiloyear timescale.",
keywords = "Miyakejima volcano, Slab dehydration, Timescales, U-series disequilibria",
author = "Tetsuya Yokoyama and Katsura Kobayashi and Takeshi Kuritani and Eizou Nakamura",
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T1 - Mantle metasomatism and rapid ascent of slab components beneath island arcs

T2 - Evidence from 238U-230Th-226Ra disequilibria of Miyakejima volcano, Izu arc, Japan

AU - Yokoyama, Tetsuya

AU - Kobayashi, Katsura

AU - Kuritani, Takeshi

AU - Nakamura, Eizou

PY - 2003/7/10

Y1 - 2003/7/10

N2 - 238U-230Th-226Ra systematics in lavas from Miyakejima volcano, Japan, are presented to estimate the timescale of magmatic processes beneath an island arc. Miyakejima volcano has four recent eruptive stages (Stages 1-4) starting >7000 BP. 238U-230Th-226Ra disequilibria observed in lavas with large 238U and 226Ra excesses imply metasomatism of depleted mantle by fluid-related processes. This metasomatism is also suggested by trace element and Sr-Nd-Pb isotopic systematics in the same lavas. In the equiline diagram, the trends for two magmatic stages (Stages 1 and 2) are regarded as two different isochrons with a common initial (230Th/232Th) ratio, although the trend for Stages 3 and 4 is a magma mixing line. Our model calculations show that slab-derived fluids can deliver some Th and a very rapid ascent time of the slab components in the mantle wedge (<7 kyr) is inferred. This rapid ascent can be explained by nearly instantaneous material transport in the mantle wedge by a hydrofracture model for fluid and a channel flow model for melt. Such a timescale estimate is not increased even if melting processes that enhance 226Ra are taken into account. The age difference in the equiline diagram corresponds to the interval of individual fluid-release events (13 kyr between Stages 1 and 2, and 5 kyr between Stages 2 and 3 . Thus fluid release from the slab and subsequent magma generation occur as episodic events on a several-kiloyear timescale.

AB - 238U-230Th-226Ra systematics in lavas from Miyakejima volcano, Japan, are presented to estimate the timescale of magmatic processes beneath an island arc. Miyakejima volcano has four recent eruptive stages (Stages 1-4) starting >7000 BP. 238U-230Th-226Ra disequilibria observed in lavas with large 238U and 226Ra excesses imply metasomatism of depleted mantle by fluid-related processes. This metasomatism is also suggested by trace element and Sr-Nd-Pb isotopic systematics in the same lavas. In the equiline diagram, the trends for two magmatic stages (Stages 1 and 2) are regarded as two different isochrons with a common initial (230Th/232Th) ratio, although the trend for Stages 3 and 4 is a magma mixing line. Our model calculations show that slab-derived fluids can deliver some Th and a very rapid ascent time of the slab components in the mantle wedge (<7 kyr) is inferred. This rapid ascent can be explained by nearly instantaneous material transport in the mantle wedge by a hydrofracture model for fluid and a channel flow model for melt. Such a timescale estimate is not increased even if melting processes that enhance 226Ra are taken into account. The age difference in the equiline diagram corresponds to the interval of individual fluid-release events (13 kyr between Stages 1 and 2, and 5 kyr between Stages 2 and 3 . Thus fluid release from the slab and subsequent magma generation occur as episodic events on a several-kiloyear timescale.

KW - Miyakejima volcano

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