著者

Junji Yamamoto Hidemi Ishibashi Yuuki Hagiwara Lena Yokokura Kiyoaki Niida

出版者

GEOCHEMICAL SOCIETY OF JAPAN

雑誌

GEOCHEMICAL JOURNAL (ISSN:00167002)

巻号頁・発行日

vol.56, no.1, pp.31-39, 2022 (Released:2022-02-28)

参考文献数

36

被引用文献数

1

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In the Horoman peridotite complex, the peridotite containing olivine-filled channels is known to exist. To examine the distribution pattern of the channel olivine, we performed non-destructive microanalyses of Raman spectra at 51 points of the olivine with 5 mm intervals along the channel. Compared with the Raman spectra of a reference euhedral olivine, for which the crystallographic orientation is known, there is no abrupt change in the crystallographic orientation in the 250 mm line analysis region of the channel. Moreover, Mg/Fe ratios of the channel olivine show gradual change over the entire measured area. If the channel olivine is an aggregate of olivine grains crystallized from magma infiltrating into the channel, then there should be olivine grains with both uneven crystallographic orientation and a homogeneous Mg/Fe ratio. Therefore, the olivine in the channel is regarded as a single crystal with slight growth zoning. The peridotite with the channel had been a part of mantle that was uplifted by the collision of plates. Therefore, the channel is a trace of magma migrating in the mantle. Magma migration in mantle drives the material–thermal circulation system connecting the Earth’s interior and surface. Furthermore, the size of the mineral in mantle reflects its stress field. Therefore, the magma channel involving such a large olivine is a unique specimen that reveals the particular characteristics of magmatism occurring in the Earth’s interior.

著者

Risako HATADA Hidemi ISHIBASHI Yukiko SUWA Yusuke SUZUKI Natsumi HOKANISHI Atsushi YASUDA

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.190724, (Released:2020-06-26)

被引用文献数

1

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We conducted textural and chemical analyses of melt inclusions and their host plagioclase crystals in the scoria of the Izu–Omuroyama monogenetic volcano, erupted at ~ 4 ka in the Higashi–Izu monogenetic volcanic field, Japan. The groundmass melt was andesitic with ~ 59–61 wt% SiO2, and it contained abundant microphenocrysts of olivine and plagioclase. In contrast, ~ 59% of the plagioclase–hosted melt inclusions have rhyolitic compositions with ~ 70–75 wt% SiO2. The host plagioclase phenocrysts have cores with An# of 44.7 ± 4.2 [An# = 100Ca/(Ca + Na) in mol] and rims with An# of 68–78, and the calcic rims have compositions similar to the microphenocrysts. The cores of the host plagioclase phenocrysts have FeO* and K2O contents that are in equilibrium with the rhyolitic melt inclusions. Using the plagioclase–melt geohygrometers and assuming temperatures of 790–850 °C, we estimated the H2O contents of the rhyolitic melt inclusions to be ~ 4.4–10.2 wt%, indicating H2O–saturation depths of >4.5 km. Our results suggest that an inhibited reservoir of plagioclase–bearing rhyolitic melt existed beneath the monogenetic volcano at the time of the scoria eruption, which was ~ 800 years earlier than the first rhyolitic eruption in the volcanic field. Plagioclase content in the silicic reservoir is estimated to be less than 35.8%, suggesting the magma was eruptible. Our results demonstrate the potential usefulness of plagioclase–hosted melt inclusions for indicating the existence of such an inhibited silicic magma.