Boron in metapelites controlled by the breakdown of tourmaline and retrograde formation of borosilicates in the Yanai area, Ryoke metamorphic belt, SW Japan

Tetsuo Kawakami, Takeshi Ikeda

Research output: Contribution to journalArticlepeer-review

32 Citations (Scopus)

Abstract

Tourmaline-out isograd formed by the breakdown of tourmaline is defined in the upper amphibolite-facies metapelites in the Yanai area, Ryoke metamorphic belt, SW Japan. The rim composition of tourmaline progressively becomes aluminous with ascending metamorphic grade, and the chemical zoning of tourmaline is controlled by X□AlNa 1Mg-1 and MgTiY- Al-2 vectors in low- to medium-grade zones where muscovite is stable, whereas it is controlled by Mg(OH)Y Al-1O-1, CaMgOX-1 Y Al-1(OH -1 and MgTiY Al-2 vectors in further higher-grade, muscovite-unstable zones. The size of tourmaline increases drastically where breakdown of muscovite + quartz takes place, probably due to the growth of tourmaline during breakdown of muscovite. On the high-temperature side of the tourmaline-out isograd, depletion of whole-rock boron is observed. Escape of boron-bearing melt or the fluid evolved from the melt during its crystallization probably caused this depletion, although locally trapped, boron-bearing melt or fluid formed irregularly shaped tourmaline and dumortierite during retrograde metamorphism.

Original languageEnglish
Pages (from-to)131-150
Number of pages20
JournalContributions to Mineralogy and Petrology
Volume145
Issue number2
DOIs
Publication statusPublished - May 2003

All Science Journal Classification (ASJC) codes

  • Geophysics
  • Geochemistry and Petrology

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