著者

Sota NIKI Kenta YOSHIDA Hikaru SAWADA Ryosuke OYANAGI Takafumi HIRATA

出版者

Japan Association of Mineralogical Sciences

雑誌

Journal of Mineralogical and Petrological Sciences (ISSN:13456296)

巻号頁・発行日

vol.117, no.1, pp.210814, 2022 (Released:2022-05-18)

参考文献数

24

被引用文献数

1

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Here we first report the in situ U–Pb dating of metamorphic grossular garnet (Grs) with distinction between internal zonation textures. The studied Grs occurs in an eclogite–facies marble collected from the eastern Iratsu body of the Sanbagawa metamorphic terrane, Japan. The Grs has a patchy texture, predominantly with pure Grs cores and andradite (Adr)–rich rims formed during eclogite–facies and exhumation stages, respectively. The U–Pb ages for the Grs core and Adr–rich rim were 97 ± 10 and 106 ± 16 Ma (95% confidence level), respectively. Despite the compositional zoning formed under different P–T conditions, the U–Pb ages of the core and rim were in similar values within analytical uncertainties. This decoupling of chemical zonation and U–Pb ages implies that the U–Pb chronological signatures of rims were inherited from cores owing to the redistribution of radiogenic Pb in cores during the rim formation through fluid–mediated dissolution and reprecipitation. The Grs U–Pb age (97 ± 10 Ma) thus directly corresponds to previously reported P–T conditions of the core formation during the eclogite–facies metamorphism. This advantage of Grt petrochronology as the combination of radiometric ages obtained by in situ analysis and P–T conditions deduced from paragenesis can contribute to reconstruct reliable metamorphic histories.

著者

Kenta YOSHIDA Sota NIKI Hikaru SAWADA Ryosuke OYANAGI

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.200730, (Released:2020-12-08)

被引用文献数

2

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Datolite [CaBSiO4(OH)] was discovered in an eclogite–facies calcite marble collected from the Eastern Iratsu body in the Sanbagawa metamorphic belt of central Shikoku. The marble was composed of calcite, diopside, and garnet that contained inclusions of omphacite. Enclosed in the marble is a pod composed mainly of quartz, with subordinate calcite, diopside, and garnet that has inclusions of datolite. The formation conditions of the datolite were estimated on the basis of mineral assemblage and the Raman elastic geobarometer to be approximately 400–650 °C and 0.8–1.3 GPa, which coincide with the conditions of the eclogite juxtaposition with the non–eclogite units in the Besshi district. Our study records the highest pressure–temperature conditions as the metamorphic datolite formation. Our findings provide evidence for the occurrence of B–rich fluid infiltration during the juxtaposition of eclogite unit with the non–eclogite unit in the Besshi district.

著者

Kanoko Kurihara Norika Numa Sota Niki Mai Akamune Masaki Nakazato Shuji Yamashita Shoichi Itoh Takafumi Hirata

出版者

GEOCHEMICAL SOCIETY OF JAPAN

雑誌

GEOCHEMICAL JOURNAL (ISSN:00167002)

巻号頁・発行日

vol.57, no.5, pp.e9-e16, 2023 (Released:2023-10-24)

参考文献数

35

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Elemental and isotopic analyses of individual submicron-sized particles in chondrite matrix were made by an inductively coupled plasma time-of-flight mass spectrometer (ICP-TOF-MS) and a multiple collector ICP-MS equipped with high-time-resolution ion counters (HTR-MC-ICP-MS). The particles were collected from Allende CV3 chondrite through a laser ablation-in-liquid (LAL) technique. Firstly, the abundances for four major elements (Si, Al, Mg, and Fe) were determined on total 6086 particles, indicating that the Allende matrix is a mixture of submicron-sized particles made mainly of olivine, pyroxene, spinel, Fe–Ni sulfide, and Fe–Ni metal, consistent with the predicted major constituent minerals by a nebular condensation model. The major elemental compositions revealed that Fe–Ni particles are minor components (about 0.3% in number fraction) in the Allende matrix. Then, to estimate the origin of these metallic particles, abundances for Ni and two minor elements (Os and Pt) were measured. Total 10417 particles of Ni–Os–Pt bearing particles were also found in the chondrite matrix. Majority of the particles were enriched in Ni. Os and Pt were present as separated particles, and no particles with presence of both the Os and Pt were found. Finally, with the HTR-MC-ICP-MS technique, 195Pt/194Pt value was measured on total 1545 particles. The resulting 195Pt/194Pt values agree with the solar composition within analytical uncertainties. This lack in isotopic anomalies of the 195Pt/194Pt can be explained either by majority of the Pt nuggets being produced from uniform reservoir in the solar system or by Pt being isotopically homogenized prior to the formation of the solar nebula.

著者

Raiki YAMADA Hikaru SAWADA Shinnosuke AOYAMA Wataru OUCHI Sota NIKI Mitsuhiro NAGATA Toshiro TAKAHASHI Takafumi HIRATA

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.201125, (Released:2021-02-25)

被引用文献数

8

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The Hida granites, classified into the pre–Jurassic and Jurassic plutons in this study, are important components of the Hida belt, which is a Paleozoic–Mesozoic basement of the Japan arc and underwent Permian to Triassic metamorphism during the collision between the North and South China blocks. This study performed zircon U–Pb dating and whole–rock geochemical analyses for the Hida granites from the major plutonic bodies to reveal the geotectonic history and the origin of the Hida belt. Obtained 238U–206Pb weighted mean ages exhibit 239.1–238.3 Ma for the Katakaigawa body (augen granite) and 200.5–180.9 Ma for the other bodies (non–deformed granitoids), and these ages can be correlated to the pre–Jurassic and Jurassic plutons, respectively. Geochronological results suggest that the mylonitization forming augen granites of the pre–Jurassic plutons occurred during its intrusion and indicate that the Jurassic plutons are distributed widely in the Japan Sea side of the Hida belt. Meanwhile, geochemical characteristics of whole–rock major and trace element compositions indicate that the pre–Jurassic and Jurassic plutons seem difficult to distinguished geochemically and suggest that both of them are adakitic and non–adakitic granites generated in subduction zone.