Shift and rotation of composition trends by magma mixing

1983 eruption at Miyake-jima Volcano, Japan

Takeshi Kuritani, Tetsuya Yokoyama, Katsura Kobayashi, Eizou Nakamura

Research output: Contribution to journalArticle

28 Citations (Scopus)

Abstract

Pre-eruption processes are investigated for magmas erupted in 1983 from Miyake-jima volcano, which is one of the most active volcanoes in Japan. The whole-rock compositional trends of the eruptive products are principally smooth and linear. Magmas erupted from some fissures have compositions that deviate from the main linear trend. Phenocryst contents of samples displaced from the linear compositional trends are significantly lower than those of samples on the main trends. Anorthite-rich plagioclase phenocrysts, present throughout the 1983 products, are too calcic to have crystallized from the erupted magma composition, and were derived from a basaltic magma through magma mixing. Although the linear whole-rock composition trends favor simple two-component magma mixing, this cannot explain the presence of samples that deviate from the main trend. Instead, the observed composition trends were formed by mixing of a homogeneous basaltic magma with andesitic magmas exhibiting compositional diversity. The original linear composition trends of the andesitic end-member magma were rotated and shifted to the direction of the basaltic end-member magma by magma mixing. The samples out of the main trends represent magmas with less basaltic component than those on the trend. The density and viscosity of the basaltic end-member magma were comparable with those of the andesitic end-member magmas. The basaltic magma, discharged from one magma chamber at ∼2 kbar pressure, was injected into a magma chamber at lower pressure occupied by the chemically zoned andesite magma (∼1 kbar), and possibly as a fountain. To establish the characteristic mixing trend of the 1983 magma, the basaltic component must have been distributed systematically in the zoned andesite magma. A requirement is that the basaltic magma spread laterally and mixed with the andesite magma at various levels of ascent of the fountain in the host andesite magma. Analysis of compositional zoning in titanomagnetite crystals revealed that the eruption of the 1983 magmas was initiated soon after the replenishment of the basaltic magma in the 1 kbar magma chamber.

Original languageEnglish
Pages (from-to)1895-1916
Number of pages22
JournalJournal of Petrology
Volume44
Issue number10
Publication statusPublished - Oct 2003

Fingerprint

Volcanoes
volcanoes
volcanic eruptions
magma
Japan
volcano
volcanic eruption
trends
shift
Fountains
Chemical analysis
Rocks
Zoning
andesite
magma chamber
trend
Viscosity
Crystals
chambers
rocks

Keywords

  • Compositional trend
  • Liquid-liquid blending
  • Magma chamber
  • Magma mixing
  • Miyake-jima Volcano

ASJC Scopus subject areas

  • Geochemistry and Petrology
  • Geophysics

Cite this

Shift and rotation of composition trends by magma mixing : 1983 eruption at Miyake-jima Volcano, Japan. / Kuritani, Takeshi; Yokoyama, Tetsuya; Kobayashi, Katsura; Nakamura, Eizou.

In: Journal of Petrology, Vol. 44, No. 10, 10.2003, p. 1895-1916.

Research output: Contribution to journalArticle

@article{50bbf4789f944e419579400e25fbb8ed,
title = "Shift and rotation of composition trends by magma mixing: 1983 eruption at Miyake-jima Volcano, Japan",
abstract = "Pre-eruption processes are investigated for magmas erupted in 1983 from Miyake-jima volcano, which is one of the most active volcanoes in Japan. The whole-rock compositional trends of the eruptive products are principally smooth and linear. Magmas erupted from some fissures have compositions that deviate from the main linear trend. Phenocryst contents of samples displaced from the linear compositional trends are significantly lower than those of samples on the main trends. Anorthite-rich plagioclase phenocrysts, present throughout the 1983 products, are too calcic to have crystallized from the erupted magma composition, and were derived from a basaltic magma through magma mixing. Although the linear whole-rock composition trends favor simple two-component magma mixing, this cannot explain the presence of samples that deviate from the main trend. Instead, the observed composition trends were formed by mixing of a homogeneous basaltic magma with andesitic magmas exhibiting compositional diversity. The original linear composition trends of the andesitic end-member magma were rotated and shifted to the direction of the basaltic end-member magma by magma mixing. The samples out of the main trends represent magmas with less basaltic component than those on the trend. The density and viscosity of the basaltic end-member magma were comparable with those of the andesitic end-member magmas. The basaltic magma, discharged from one magma chamber at ∼2 kbar pressure, was injected into a magma chamber at lower pressure occupied by the chemically zoned andesite magma (∼1 kbar), and possibly as a fountain. To establish the characteristic mixing trend of the 1983 magma, the basaltic component must have been distributed systematically in the zoned andesite magma. A requirement is that the basaltic magma spread laterally and mixed with the andesite magma at various levels of ascent of the fountain in the host andesite magma. Analysis of compositional zoning in titanomagnetite crystals revealed that the eruption of the 1983 magmas was initiated soon after the replenishment of the basaltic magma in the 1 kbar magma chamber.",
keywords = "Compositional trend, Liquid-liquid blending, Magma chamber, Magma mixing, Miyake-jima Volcano",
author = "Takeshi Kuritani and Tetsuya Yokoyama and Katsura Kobayashi and Eizou Nakamura",
year = "2003",
month = "10",
language = "English",
volume = "44",
pages = "1895--1916",
journal = "Journal of Petrology",
issn = "0022-3530",
publisher = "Oxford University Press",
number = "10",

}

TY - JOUR

T1 - Shift and rotation of composition trends by magma mixing

T2 - 1983 eruption at Miyake-jima Volcano, Japan

AU - Kuritani, Takeshi

AU - Yokoyama, Tetsuya

AU - Kobayashi, Katsura

AU - Nakamura, Eizou

PY - 2003/10

Y1 - 2003/10

N2 - Pre-eruption processes are investigated for magmas erupted in 1983 from Miyake-jima volcano, which is one of the most active volcanoes in Japan. The whole-rock compositional trends of the eruptive products are principally smooth and linear. Magmas erupted from some fissures have compositions that deviate from the main linear trend. Phenocryst contents of samples displaced from the linear compositional trends are significantly lower than those of samples on the main trends. Anorthite-rich plagioclase phenocrysts, present throughout the 1983 products, are too calcic to have crystallized from the erupted magma composition, and were derived from a basaltic magma through magma mixing. Although the linear whole-rock composition trends favor simple two-component magma mixing, this cannot explain the presence of samples that deviate from the main trend. Instead, the observed composition trends were formed by mixing of a homogeneous basaltic magma with andesitic magmas exhibiting compositional diversity. The original linear composition trends of the andesitic end-member magma were rotated and shifted to the direction of the basaltic end-member magma by magma mixing. The samples out of the main trends represent magmas with less basaltic component than those on the trend. The density and viscosity of the basaltic end-member magma were comparable with those of the andesitic end-member magmas. The basaltic magma, discharged from one magma chamber at ∼2 kbar pressure, was injected into a magma chamber at lower pressure occupied by the chemically zoned andesite magma (∼1 kbar), and possibly as a fountain. To establish the characteristic mixing trend of the 1983 magma, the basaltic component must have been distributed systematically in the zoned andesite magma. A requirement is that the basaltic magma spread laterally and mixed with the andesite magma at various levels of ascent of the fountain in the host andesite magma. Analysis of compositional zoning in titanomagnetite crystals revealed that the eruption of the 1983 magmas was initiated soon after the replenishment of the basaltic magma in the 1 kbar magma chamber.

AB - Pre-eruption processes are investigated for magmas erupted in 1983 from Miyake-jima volcano, which is one of the most active volcanoes in Japan. The whole-rock compositional trends of the eruptive products are principally smooth and linear. Magmas erupted from some fissures have compositions that deviate from the main linear trend. Phenocryst contents of samples displaced from the linear compositional trends are significantly lower than those of samples on the main trends. Anorthite-rich plagioclase phenocrysts, present throughout the 1983 products, are too calcic to have crystallized from the erupted magma composition, and were derived from a basaltic magma through magma mixing. Although the linear whole-rock composition trends favor simple two-component magma mixing, this cannot explain the presence of samples that deviate from the main trend. Instead, the observed composition trends were formed by mixing of a homogeneous basaltic magma with andesitic magmas exhibiting compositional diversity. The original linear composition trends of the andesitic end-member magma were rotated and shifted to the direction of the basaltic end-member magma by magma mixing. The samples out of the main trends represent magmas with less basaltic component than those on the trend. The density and viscosity of the basaltic end-member magma were comparable with those of the andesitic end-member magmas. The basaltic magma, discharged from one magma chamber at ∼2 kbar pressure, was injected into a magma chamber at lower pressure occupied by the chemically zoned andesite magma (∼1 kbar), and possibly as a fountain. To establish the characteristic mixing trend of the 1983 magma, the basaltic component must have been distributed systematically in the zoned andesite magma. A requirement is that the basaltic magma spread laterally and mixed with the andesite magma at various levels of ascent of the fountain in the host andesite magma. Analysis of compositional zoning in titanomagnetite crystals revealed that the eruption of the 1983 magmas was initiated soon after the replenishment of the basaltic magma in the 1 kbar magma chamber.

KW - Compositional trend

KW - Liquid-liquid blending

KW - Magma chamber

KW - Magma mixing

KW - Miyake-jima Volcano

UR - http://www.scopus.com/inward/record.url?scp=0142248130&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0142248130&partnerID=8YFLogxK

M3 - Article

VL - 44

SP - 1895

EP - 1916

JO - Journal of Petrology

JF - Journal of Petrology

SN - 0022-3530

IS - 10

ER -