The Late Jurassic magmatic protoliths of the Mikabu greenstones in SW Japan: A fragment of an oceanic plateau in the Paleo-Pacific Ocean

Sawada, Hikaru; Isozaki, Yukio; Aoki, Shogo; Sakata, Shuhei; Sawaki, Yusuke; Hasegawa, Ryô; Nakamura, Yasuo

doi:10.1016/j.jseaes.2018.08.018

Cited by 20 publications

(6 citation statements)

References 43 publications

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“…Although the zircon U–Pb age of mafic rocks in Sambagawa metamorphic rocks is not well known, this age is consistent with the zircon U–Pb age of gabbro in Mikabu Unit according to the previous reports (e.g. Sawada et al, 2019). Nozaki, Kato, and Suzuki (2013) reported the Re‐Os ages ranging from 155 to 144 Ma from the 11 Besshi‐type sulphide deposits and concluded them as the formation age of the protolith of the mafic schist at the Mid Ocean Ridge.…”

Section: Discussionsupporting

confidence: 90%

Zircon U–Pb geochronology of “Sashu mylonite”, eastern extension of Higo Plutono‐metamorphic Complex, Southwest Japan: Implication for regional tectonic evolution

et al. 2020

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Geochronological and geochemical studies reveal the possible origin of the restricted body of mylonite rocks occurring at the eastern edge of Kyushu Island, Japan, just in contact with the Sashu Fault, a part of the Paleo-Median Tectonic Line (Paleo-MTL). The LA-ICP-MS zircon U-Pb dating of the quartz diorite mylonite in this mylonitic body indicates a crystallization age of 114.0 ±1.7 Ma. Moreover, the two tonalite samples appear as thin layers within the Permian fine-grained mafic mylonite; a part of the same body yields the age of 113.7 ±2.3 Ma and 116.9 ±1.3 Ma, with extremely low Th/U ratio. These quartz diorite mylonite and tonalite are consistent with the late Early Cretaceous magmatism and coeval metamorphism similar to those in the Higo Plutono-metamorphic Complex in western Kyushu, Japan. This newly characterized complex occurs just south of the Creta

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Section: Discussionsupporting

confidence: 90%

Zircon U–Pb geochronology of “Sashu mylonite”, eastern extension of Higo Plutono‐metamorphic Complex, Southwest Japan: Implication for regional tectonic evolution

et al. 2020

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“…Tominaga and Hara [13] noted that the Kashiwagi Unit and the Mikabu greenstones are closely related in the ocean plate stratigraphy. Previously, the Mikabu greenstones were thought to have originated from an oceanic plateau related to the Shatsky Rise at the nearby triple junction of the Izanagi, Farallon, and Pacific plates during the Late Jurassic [40,41]. However, Tominaga and Hara [13], based on a U-Pb age of 157 Ma from anorthosite, proposed that the oceanic plateau was formed in the central part of the Izanagi Plate and that eruption occurred in the Late Jurassic.…”

Section: Low-grade Sanbagawa Metamorphismmentioning

confidence: 99%

Progressive Low-Grade Metamorphism Reconstructed from the Raman Spectroscopy of Carbonaceous Material and an EBSD Analysis of Quartz in the Sanbagawa Metamorphic Event, Central Japan

Hara

Mori

Tominaga³

et al. 2021

Minerals

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Low-grade metamorphic temperature conditions associated with the Sanbagawa metamorphic event were estimated by the Raman spectroscopy of carbonaceous material (RSCM) in pelitic rocks and an electron backscatter diffraction (EBSD) analysis of the quartz in siliceous rocks. Analytical samples were collected from the Sanbagawa metamorphic complex, the Mikabu greenstones, and the Chichibu accretionary complex in the eastern Kanto Mountains, central Japan. Previously, low-grade Sanbagawa metamorphism was only broadly recognized as pumpellyite–actinolite facies assigned to the chlorite zone. The RSCM results indicate metamorphic temperatures of 358 °C and 368 °C for the chlorite zone and 387 °C for the garnet zone of the Sanbagawa metamorphic complex, 315 °C for the Mikabu greenstones, and 234–266 °C for the Chichibu accretionary complex. From the EBSD analyses, the diameter of the quartz grains calculated by the root mean square (RMS) approximation ranges from 55.9 to 69.0 μm for the Sanbagawa metamorphic complex, 9.5 to 23.5 μm for the Mikabu greenstones, and 2.9 to 7.3 μm for the Chichibu accretionary complex. The opening angles of the c-axis fabric approximate 40–50°, presenting temperatures of 324–393 °C for the Sanbagawa metamorphic complex and the Mikabu greenstones. The temperature conditions show a continuous increase with no apparent gaps from these low-grade metamorphosed rocks. In addition, there exists an empirical exponential relationship between the estimated metamorphic temperatures and the RMS values of the quartz grains. In this study, integrated analyses of multiple rock types provided valuable information on progressive low-grade metamorphism and a similar approach may be applied to study other metamorphic complexes.

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“…The data were acquired for multiple groups of five spot analyses of unknown grains bracketed by one analysis of NIST SRM610 glass. The analytical precision and accuracy were evaluated by the method in Sawada et al (). More detailed procedures of this analysis are given in Appendix S3.…”

Section: Methodsmentioning

confidence: 99%

“…All uncertainties are quoted at a 2-sigma level, to which repeatability of each six measurements of 91500 zircon and NIST SRM612 glass data bracketing unknown sample groups is propagated. Plešovice zircon (Sláma et al, 2008) The analytical precision and accuracy were evaluated by the method in Sawada et al (2019). More detailed procedures of this analysis are given in Appendix S3.…”

Section: U-pb Analysismentioning

confidence: 99%

Origin of the Tonaru body in the Sanbagawa metamorphic belt, SW Japan

Aoki

Chiba

et al. 2019

Island Arc

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Zircon U-Pb dating of the Tonaru metagabbro body in the Sanbagawa metamorphic belt, southwest Japan, suggests that igneous events at ca 200-180 Ma were involved in the protolith formation. The trace element compositions of the Tonaru zircons are enriched in U (a fluid-mobile element) and Sc (an amphibole-buffered element), and depleted in Nb (a fluid-immobile element), suggesting that the parental magmas related to the Tonaru metagabbros formed in an arc setting. Integration of our results with previous studies of the metasedimentary rocks in the Tonaru body clearly indicates that the protoliths of the Tonaru body were produced by oceanic-arc magmatism. With the previous geochronological and geological studies, the tectonomagmatic-metamorphic history of the Tonaru and other mafic bodies in the Sanbagawa metamorphic belt may be summarized as follows: (i) the protolith formation by the oceanic-arc magmatic event had occurred at 200-180 Ma; (ii) the protoliths were accreted in the trench at ca 130-120 Ma; and (iii) they were completely subducted into the depth of the eclogite-facies condition after 120 Ma.

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The Late Jurassic magmatic protoliths of the Mikabu greenstones in SW Japan: A fragment of an oceanic plateau in the Paleo-Pacific Ocean

Cited by 20 publications

References 43 publications

Zircon U–Pb geochronology of “Sashu mylonite”, eastern extension of Higo Plutono‐metamorphic Complex, Southwest Japan: Implication for regional tectonic evolution

Zircon U–Pb geochronology of “Sashu mylonite”, eastern extension of Higo Plutono‐metamorphic Complex, Southwest Japan: Implication for regional tectonic evolution

Progressive Low-Grade Metamorphism Reconstructed from the Raman Spectroscopy of Carbonaceous Material and an EBSD Analysis of Quartz in the Sanbagawa Metamorphic Event, Central Japan

Origin of the Tonaru body in the Sanbagawa metamorphic belt, SW Japan

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