- 著者
- Masaki ENAMI Aya NISHII Takashi MOURI Motohiro TSUBOI Yui KOUKETSU
- 出版者
- Japan Association of Mineralogical Sciences
- 雑誌
- Journal of Mineralogical and Petrological Sciences (ISSN:13456296)
- 巻号頁・発行日
- pp.201204, (Released:2021-05-20)
- 被引用文献数
- 1
Olivine is a major mineral in ultramafic and mafic rocks. Due to the higher Mg/Fe partition coefficient of olivine than the coexisting phases, the occurrences of Mg–poorer olivine grains, especially with Mg#[= Mg/(Mg + Fe2+)] = 0.2–0.6, are rarely reported, and thus, their spectroscopic data are limited. Fe–rich olivine phenocrysts showing compositional zoning with Mg# = ~ 0.5 (core) and ~ 0.3 (rim) and microphenocrysts with Mg# = ~ 0.4 (core) and ~ 0.2 (rim) occur in basaltic trachyandesite of Miocene Shitara volcanic rocks in central Japan. These olivine grains were investigated by Raman spectroscopy. Combining our data with the published values, we have revised the equation for Mg#–Raman spectrum relationship proposed by Mouri and Enami (2008) as follows: Mg# = 0.005446ω 2 − 0.20259ω + 1.8442 (correlation coefficient r 2 = 0.984), where ω is the difference between the doublet peak positions (κ2 − κ1).
- 著者
- Tomoki TAGUCHI Masaki ENAMI
- 出版者
- 一般社団法人日本鉱物科学会
- 雑誌
- Journal of Mineralogical and Petrological Sciences (ISSN:13456296)
- 巻号頁・発行日
- vol.109, no.4, pp.169-176, 2014 (Released:2014-08-25)
- 参考文献数
- 48
- 被引用文献数
- 4 20 2
Coexistence of jadeite (Jd92) and quartz was newly found in an inner segment of a composite–zoned garnet from a metapelite in the southern albite–biotite zone of the Asemi–gawa region, Sanbagawa belt in central Shikoku, Japan. The assemblage of jadeite + quartz in garnet gives a minimum metamorphic pressure of 1.4–1.9 GPa at 500–700 °C, which was significantly higher than that previously proposed for epidote–amphibolite facies conditions in the albite–biotite zone. Garnet includes quartz retaining high residual pressure (Δω1 values up to 11.7 cm−1), which is comparable to the residual pressure reported in eclogite and metapelite within the eclogite unit in central Shikoku. These results imply that (1) the inner segment of the composite–zoned garnet records prograde recrystallization under high–pressure blueschist to eclogite facies conditions and (2) at least a part of the southern albite–biotite zone of the Asemi–gawa region recrystallized under higher pressure conditions prior to the regional metamorphism from the greenschist to epidote–amphibolite facies that formed the regional thermal structure of the Sanbagawa belt of central Shikoku.
- 著者
- Masaki ENAMI Shuaimin HUANG Motohiro TSUBOI Yuki WAKASUGI
- 出版者
- Japan Association of Mineralogical Sciences
- 雑誌
- Journal of Mineralogical and Petrological Sciences (ISSN:13456296)
- 巻号頁・発行日
- pp.181107a, (Released:2020-12-05)
- 被引用文献数
- 1
The Tonaru epidote–amphibolite is one of the large metagabbro dominated bodies and occurs in schistose rocks of the Sanbagawa metamorphic belt, central Shikoku. This body locally retains mineral parageneses of eclogite facies equilibrium prior to the epidote–amphibolite facies stage. The lithologic boundary between the epidote–amphibolite and the surrounding schistose rocks was well observed along the Kokuryo River in the western part of the Besshi region in central Shikoku. Boundary zone of 1.5–2.5 m wide is developed between the epidote–amphibolite and pelitic schist. This zone is composed of a basic layer and alternating layers consisting of thin amphibole–rich and mica–rich bands, which occupy the epidote–amphibolite and pelitic schist sides, respectively. The basic layer has a chondrite–normalized rare–earth element (REE) pattern with slight enrichment of light REEs, which corresponds to epidote–amphibolite. By contrast, the amphibole–rich band has a flat REE pattern similar to the basic schist of the Sanbagawa belt. The basic layer in the boundary zone and epidote–amphibolite have composite–zoned garnet, showing a compositional discontinuity between the core and mantle parts, similar to that in the Sanbagawa eclogite unit. Garnet in the amphibole–rich and mica–rich bands of the alternating layers and pelitic schist shows simple normal zoning, which commonly occurs in the Sanbagawa non–eclogite unit. Sodic plagioclase occurs as inclusions in the mantle part of the composite–zoned garnet and normally zoned garnet as well as in a matrix phase. These lithologies belong to the oligoclase–biotite zone with equilibrium pressure/temperature conditions of 1.1–1.2 GPa/595–625 °C; discontinuity of metamorphic grade is not detected throughout the outcrop for the epidote–amphibolite facies stage. These data suggest that (1) the basic layer is the fractured part of the epidote–amphibolite and (2) the tectonic boundary between the eclogite and non–eclogite units corresponds to the lithologic boundary between the basic layer and alternating layers of thin amphibole–rich and mica–rich bands in the boundary zone.