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

Hikaru Sawada Tsuyoshi Iizuka Yukiyasu Tsutsumi Yukio Isozaki

出版者

GEOCHEMICAL SOCIETY OF JAPAN

雑誌

GEOCHEMICAL JOURNAL (ISSN:00167002)

巻号頁・発行日

vol.53, no.3, pp.171-179, 2019 (Released:2019-06-11)

参考文献数

64

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To understand the timing and mode of crustal production and reworking in the Archean, we performed U-Pb and Hf isotopic analyses of detrital zircon grains from the ca. 2.3 Ga Murmac Bay Group in the Rae Craton, central Canada. The zircon U-Pb ages range from 3.9 to 2.3 Ga with a significant gap interval of 3.6–3.3 Ga, indicating that felsic magmatism has semi-continuously within the craton since the early Archean. The combined U-Pb and Hf isotopic data define three distinct Hf isotope-age arrays that share a similar slope equivalent to that of typical 176Lu/177Hf ratio of continental crust, and the slope intersects the mantle evolution curve at 2.9–2.6, 3.3–3.2, and 3.8–3.6 Ga. The secular trends in zircon Hf isotopes illustrate episodic crust formation from depleted mantle during the three periods with subsequent reworking of pre-existing crusts into younger granitoids. Furthermore, these results infer that granitoid crust was rarely reworked for more than 800 million years after its formation. This finding is well explained by assuming that the Archean Rae block has grown outward from the interior by adding new crusts through subduction-related magmatism and/or by secondary accretion of exotic arc crusts. In such a tectonic framework, younger crusts were likely utilized more preferentially in crustal melting during subduction-related magmatism. These observations suggest that plate subduction has operated already in the early Archean, as early as 3.6 Ga Eoarchean.

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.