Medium P/T metamorphism in a subduction zone: A new type of regional metamorphism in Japanese accretionary complexes, inferred from b cell dimension of potassic white mica

Soichi Osozawa, Toru Koitabashi, Seiko Katsube, Martin Flower

Research output: Chapter in Book/Report/Conference proceedingChapter

2 Citations (Scopus)

Abstract

Illite crystallinity (IC) and b cell dimension from potassic white mica have been measured for accreted metapelites found in Japanese accretionary complexes. From metamorphic mineral assemblages, some accreted high-grade metamorphic rocks are the high pressure/temperature (P/T) type. Because subduction zones are areas of relatively high pressures at low temperatures, it is reasonable to expect such high P/T rocks to develop. Our data show however, that not all the accreted rocks are of the high P/T type, but also include medium P/T rocks. This baric type is independent to the classification of accretionary complexes; coherent versus mixed, pure shear versus simple shear, but depends on the division without pelagite. Such a low and medium P/T regime is also evidenced by mineral assemblages in accreted basalts and is unrelated to the contact metamorphism. The medium P/T metamorphism is considered to be due to the thermal effect of a spreading mid-ocean ridge that is subducting under an island arc, and is a new type of regional metamorphism previously unknown.

Original languageEnglish
Title of host publicationStructural Geology
Subtitle of host publicationNew Research
PublisherNova Science Publishers, Inc.
Pages1-20
Number of pages20
ISBN (Print)9781604568271
Publication statusPublished - 2008 Dec 1

Keywords

  • B cell dimension
  • Baric type
  • Illite crystallinity (IC)
  • Japanese accretionary complexes
  • Medium P/T
  • Metamorphic grade
  • Metamorphic mineral
  • New regional metamorphism.
  • Ridge subduction

ASJC Scopus subject areas

  • Earth and Planetary Sciences(all)

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