Research progress in the Chichibu Composite Belt-Reports from western Shikoku. Unit division for the Chichibu Composite Belt from a view point of accretionary tectonics and geology of western Shikoku, Japan.

Matsuoka, Atsushi; Yamakita, Satoshi; Sakakibara, Masayuki; Hisada, Ken‐ichiro

doi:10.5575/geosoc.104.634

Cited by 102 publications

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“…(Banno and Sakai, 1989) Since the degree of metamorphism increased progressively from the Chichibu belt to the Sanbagawa belt, it was believed that the Sanbagawa belt was a metamorphosed part of the Chichibu belt (e.g., Seki, 1958;Iwasaki, 1963;Banno, 1964;Toriumi, 1975). By conducting microfossil studies, the accretionary age of the Chichibu belt was found to be Middle Jurassic to earliest Cretaceous (Matsuoka et al, 1998). The Rb -Sr whole -rock age of 116 ± 10 Ma is speculated to be the age when the Sanbagawa metamorphism was at its peak (Minamishin et al, 1979).…”

Section: Introductionmentioning

confidence: 99%

SHRIMP U-Pb dating of detrital zircons from the Sanbagawa Belt, Kanto Mountains, Japan: need to revise the framework of the belt

Tsutsumi

Miyashita

Terada

et al. 2009

Journal of Mineralogical and Petrological Sciences

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Radiometric ages of detrital zircons in three samples of psammitic schists from the Sanbagawa Belt, Kanto Mountains, were obtained from the 238 U/ 206Pb ratio and isotopic compositions of Pb using a Sensitive High Resolution Ion MicroProbe (SHRIMP II). Most of the zircon ages cluster around Cretaceous, with a few ages corresponding to older zircons. The origins of the detrital zircons are mainly Cretaceous igneous rocks. The ages of the youngest zircons in samples AM48p, SnbE, and AM29p indicate Late Cretaceous time, and they are 78.8 ± 1.3 Ma, 91.4 ± 1.4 Ma, and 95.3 ±1.5 Ma, respectively. The samples AM48p and AM29p have K -Ar ages of 65.9 ± 1.4 Ma and 82.1 ± 1.8 Ma, respectively. The age difference between the youngest detrital zircon age and white mica K -Ar age is 13 Myr. The Sanbagawa Belt is believed to be a metamorphosed phase of the Chichibu Belt, which is a Middle Jurassic to earliest Cretaceous accretionary complex; however, the results of this study suggest that the protolith of the Sanbagawa belt was accreted in Late Cretaceous, similar to the Shimanto belt that runs parallel to the Sanbagawa and Chichibu belts.

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Section: Introductionmentioning

confidence: 99%

SHRIMP U-Pb dating of detrital zircons from the Sanbagawa Belt, Kanto Mountains, Japan: need to revise the framework of the belt

Tsutsumi

Miyashita

Terada

et al. 2009

Journal of Mineralogical and Petrological Sciences

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“…The composite belt consists of the Northern, Middle (Kurosegawa) and Southern belts. The Northern Chichibu belt can be traced from the Kanto Mountains in the east to western Shikoku in the west, and is comprised of five lithological units accreted during Permian (the Sawadani unit), Jurassic (the Yusugawa, Sumaizuku and Kamiyoshida units) to Early Cretaceous (the Kashiwagi unit) (Matsuoka et al, 1998). This unit division is probably applicable to the entire length of the belt, but is largely undifferentiated in many regions of this belt.…”

Section: Geologymentioning

confidence: 99%

“…The Sumaizuku unit was named after the type locality in Kanto Mountains (Matsuoka et al, 1998), but the equivalent unit in central Shikoku has been referred to as the Miyanoue Formation or Unit N-3 (Yamakita, 1988) and as the C unit (Endo and Wallis, 2017). In the study area, the Sumaizuku unit overlies the Kamiyoshida unit with a south-dipping normal fault along the contact (Endo and Wallis, 2017) (Fig.…”

Section: Geologymentioning

confidence: 99%

“…Early Permian conodont and radiolarian fossils have been reported from red chert adjacent to the Kunimiyama deposits and red chert associated with basalt lava from several localities in central Shikoku (Yamakita, 1988), suggesting stratiform ore deposits in this unit deposited near a mid-ocean ridge during the Early Permian. The age of accretion of the Sumaizuku unit has been considered to be Middle Jurassic on the basis of radiolarian fossils in mudstone (Yamakita, 1988;Matsuoka et al, 1998). Peak P-T conditions of this unit in the study area has been constrained to be0…”

Section: Geologymentioning

confidence: 99%

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Ilvaite–manganilvaite series minerals in jasper and iron–manganese ore from the Northern Chichibu belt, central Shikoku, Japan

Endo

2017

Journal of Mineralogical and Petrological Sciences

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Ilvaite, a hydrous calcium mixed-valent iron silicate, is found in red hematitic chert ( jasper) lenses in altered basalt and an iron-manganese ore from the Sumaizuku unit (Middle Jurassic accretionary complex) of the Northern Chichibu belt, SW Japan. The jasper lenses are composed of ilvaite, andradite, stilpnomelane, riebeckite, hematite and quartz. Ilvaite in the jasper lenses shows an unusual spherical morphology (~100 µm in diameter) and each ilvaite spherule exhibits a foam-like microstructure with recrystallized quartz grains. Ilvaite also occurs as discrete euhedral crystals (up to 500 µm in length) in quartz segregation veins or monomineralic ilvaite veins. Ilvaite in the jasper lenses is close to the endmember composition, but the material in the ironmanganese ore is rich in [6] Mn 2+ (up to 0.84 atoms per formula unit) corresponding to manganilvaite. Thermodynamic modeling shows that the ilvaite-andradite-hematite-quartz association (ilvaite + O 2 = hematite + andradite + quartz) is stable under the peak P-T conditions of the Sumaizuku unit (~0.35 GPa, 230-250°C) and oxygen fugacity slightly above the hematite-magnetite buffer (log f O2 =~-38). Ilvaite spherules are intimately associated with colloform-textured andradite, suggesting that they probably originated from a CaFe-Si colloidal precursor deposited along hydrothermal fluid conduits within the Early Permian oceanic crust, and recrystallized during subduction-related low-grade metamorphism.

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“…The Chichibu belt, in regions where the Kurosegawa zone is present, is subdivided into the Northern and Southern belts. According to Matsuoka et al (1998), the Northern Chichibu belt is comprised of five lithological units accreted during Permian (the Sawadani unit), Middle Jurassic (the Yusugawa, Sumaizuku and Kamiyoshida units) and Late Jurassic to the earliest Cretaceous (the Kashiwagi unit). This subdivision and unit terminology for the Northern Chichibu belt are adopted in this study.…”

Section: Geologymentioning

confidence: 99%

Jadeite–bearing metaigneous rocks from the Northern Chichibu belt, SW Japan: implications for the lowest–grade Sanbagawa metamorphism

Endo

2015

Journal of Mineralogical and Petrological Sciences

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Multiple generations of Na-Ca and Na pyroxenes (aegirine-augite, aegirine and jadeite) were found in a metamorphosed monzonitic dike from a coherent mafic layer of the Northern Chichibu belt in central Shikoku, Japan. The mafic layer was derived from alkaline basalt magma and its derivatives, and belongs to the Kamiyoshida unit (Middle Jurassic accretionary complex). The earliest-stage sodic pyroxene (jadeite-free Ti-rich aegirine-augite to aegirine) in the dike probably crystallized during a post-magmatic hydrothermal stage. Igneous Ti-rich augite phenocrysts were almost completely pseudomorphed by chlorite + phengite + Al-OH-rich titanite + sodic pyroxene (aegirine-augite with jadeite component) during early stages of subduction metamorphism. The earliest-stage sodic pyroxene and pseudomorphed Ti-rich augite were further overgrown by jadeite/ aegirine fringes during high-P/T metamorphism. Jadeite/aegirine pyroxene also occurs as small (~50 µm long) neoblasts within pseudomorphs (albite + phengite + pumpellyite ± Ba-rich K-feldspar) after igneous plagioclase. Individual grains of the fringe/neoblastic pyroxene are zoned with a jadeite core (up to 98% jadeite content) and an aegirine rim (down to 25% jadeite content). Jadeite-rich pyroxene (up to 92% jadeite content) was also found in basaltic rock from the mafic layer. The absence of quartz and the alkaline affinity of the protoliths suggest that the jadeite formation can be explained by the reaction analcime = jadeite + H 2 O. If H 2 O fluid was present, the decrease in jadeite content in the fringe/neoblastic pyroxene implies decompression from 0.6-0.7 GPa at 300°C to~0.4 GPa at 210-260°C. The formation of the jadeite-to-aegirine pyroxene during exhumation probably resulted from the lowest-grade Sanbagawa metamorphism.

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Research progress in the Chichibu Composite Belt-Reports from western Shikoku. Unit division for the Chichibu Composite Belt from a view point of accretionary tectonics and geology of western Shikoku, Japan.

Cited by 102 publications

References 0 publications

SHRIMP U-Pb dating of detrital zircons from the Sanbagawa Belt, Kanto Mountains, Japan: need to revise the framework of the belt

SHRIMP U-Pb dating of detrital zircons from the Sanbagawa Belt, Kanto Mountains, Japan: need to revise the framework of the belt

Ilvaite–manganilvaite series minerals in jasper and iron–manganese ore from the Northern Chichibu belt, central Shikoku, Japan

Jadeite–bearing metaigneous rocks from the Northern Chichibu belt, SW Japan: implications for the lowest–grade Sanbagawa metamorphism

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