Sr, Nd and Pb isotope systematics of Akagi volcano, Northeast Japan: Implications for interaction between island arc magma and lower crust

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Abstract

Isotopic compositions of Sr, Nd and Pb and REE concentrations have been determined for samples from "isotopically anomalous" Akagi volcano locating on the volcanic front of Northeast Japan Arc. The Sr isotopic compositions show a large variation with highly enriched isotope character (87Sr/86Sr=0.7060 to 0.7088) compared to those from other volcanoes on the front. The Nd isotopic compositions, ranging from εNd = -0.40 to -8.6, have a negative correlation with the Sr isotopic compositions. The Pb isotopic data along with Sr and Nd isotope systematics clearly indicate that the isotopic variations of Akagi volcano were caused by a two-component mixing between an end member isotopically similar to the primary magma on the volcanic front of Northeast Japan Arc and a lower crustal component. Chondrite-normalized REE patterns of Akagi samples show U-shaped, HREE-depleted pattern with positive Eu anomaly. Such REE features may have been developed by fractionation of amphibole formed by the reaction between a fluid-rich magma and clinopyroxene in granulitic lower crust. The fluid-rich magma could be originated from a highly metasomatized mantle wedge caused by the dehydration of oceanic slabs of the Pacific plate and the overlapping Philippine Sea Plate. Such a unique tectonic setting could result in higher water supply to the source region of magma than normal circumstances and thereby generating fluid-rich magma which could enhance assimilation of lower crust beneath Akagi volcano.

Original languageEnglish
Pages (from-to)69-73
Number of pages5
JournalProceedings of the Japan Academy Series B: Physical and Biological Sciences
Volume73
Issue number5
Publication statusPublished - May 1997

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island arcs
volcanoes
Islands
Isotopes
magma
isotopes
crusts
Japan
Meteoroids
Amphibole Asbestos
Philippines
Water Supply
Dehydration
Oceans and Seas
Philippine Sea
interactions
volcanology
fluids
arcs
slabs

Keywords

  • Akagi volcano
  • Amphibole
  • Assimilation-reaction process
  • Lower crust
  • Philippine Sea plate
  • Rare Earth Element
  • Sr, Nd and Pb isotopic composition

ASJC Scopus subject areas

  • Agricultural and Biological Sciences(all)
  • General

Cite this

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title = "Sr, Nd and Pb isotope systematics of Akagi volcano, Northeast Japan: Implications for interaction between island arc magma and lower crust",
abstract = "Isotopic compositions of Sr, Nd and Pb and REE concentrations have been determined for samples from {"}isotopically anomalous{"} Akagi volcano locating on the volcanic front of Northeast Japan Arc. The Sr isotopic compositions show a large variation with highly enriched isotope character (87Sr/86Sr=0.7060 to 0.7088) compared to those from other volcanoes on the front. The Nd isotopic compositions, ranging from εNd = -0.40 to -8.6, have a negative correlation with the Sr isotopic compositions. The Pb isotopic data along with Sr and Nd isotope systematics clearly indicate that the isotopic variations of Akagi volcano were caused by a two-component mixing between an end member isotopically similar to the primary magma on the volcanic front of Northeast Japan Arc and a lower crustal component. Chondrite-normalized REE patterns of Akagi samples show U-shaped, HREE-depleted pattern with positive Eu anomaly. Such REE features may have been developed by fractionation of amphibole formed by the reaction between a fluid-rich magma and clinopyroxene in granulitic lower crust. The fluid-rich magma could be originated from a highly metasomatized mantle wedge caused by the dehydration of oceanic slabs of the Pacific plate and the overlapping Philippine Sea Plate. Such a unique tectonic setting could result in higher water supply to the source region of magma than normal circumstances and thereby generating fluid-rich magma which could enhance assimilation of lower crust beneath Akagi volcano.",
keywords = "Akagi volcano, Amphibole, Assimilation-reaction process, Lower crust, Philippine Sea plate, Rare Earth Element, Sr, Nd and Pb isotopic composition",
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T1 - Sr, Nd and Pb isotope systematics of Akagi volcano, Northeast Japan

T2 - Implications for interaction between island arc magma and lower crust

AU - Kobayashi, Katsura

AU - Nakamura, Eizou

AU - Shibata, Tomoyuki

AU - Makishima, Akio

PY - 1997/5

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N2 - Isotopic compositions of Sr, Nd and Pb and REE concentrations have been determined for samples from "isotopically anomalous" Akagi volcano locating on the volcanic front of Northeast Japan Arc. The Sr isotopic compositions show a large variation with highly enriched isotope character (87Sr/86Sr=0.7060 to 0.7088) compared to those from other volcanoes on the front. The Nd isotopic compositions, ranging from εNd = -0.40 to -8.6, have a negative correlation with the Sr isotopic compositions. The Pb isotopic data along with Sr and Nd isotope systematics clearly indicate that the isotopic variations of Akagi volcano were caused by a two-component mixing between an end member isotopically similar to the primary magma on the volcanic front of Northeast Japan Arc and a lower crustal component. Chondrite-normalized REE patterns of Akagi samples show U-shaped, HREE-depleted pattern with positive Eu anomaly. Such REE features may have been developed by fractionation of amphibole formed by the reaction between a fluid-rich magma and clinopyroxene in granulitic lower crust. The fluid-rich magma could be originated from a highly metasomatized mantle wedge caused by the dehydration of oceanic slabs of the Pacific plate and the overlapping Philippine Sea Plate. Such a unique tectonic setting could result in higher water supply to the source region of magma than normal circumstances and thereby generating fluid-rich magma which could enhance assimilation of lower crust beneath Akagi volcano.

AB - Isotopic compositions of Sr, Nd and Pb and REE concentrations have been determined for samples from "isotopically anomalous" Akagi volcano locating on the volcanic front of Northeast Japan Arc. The Sr isotopic compositions show a large variation with highly enriched isotope character (87Sr/86Sr=0.7060 to 0.7088) compared to those from other volcanoes on the front. The Nd isotopic compositions, ranging from εNd = -0.40 to -8.6, have a negative correlation with the Sr isotopic compositions. The Pb isotopic data along with Sr and Nd isotope systematics clearly indicate that the isotopic variations of Akagi volcano were caused by a two-component mixing between an end member isotopically similar to the primary magma on the volcanic front of Northeast Japan Arc and a lower crustal component. Chondrite-normalized REE patterns of Akagi samples show U-shaped, HREE-depleted pattern with positive Eu anomaly. Such REE features may have been developed by fractionation of amphibole formed by the reaction between a fluid-rich magma and clinopyroxene in granulitic lower crust. The fluid-rich magma could be originated from a highly metasomatized mantle wedge caused by the dehydration of oceanic slabs of the Pacific plate and the overlapping Philippine Sea Plate. Such a unique tectonic setting could result in higher water supply to the source region of magma than normal circumstances and thereby generating fluid-rich magma which could enhance assimilation of lower crust beneath Akagi volcano.

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