Phase relations of lawsonite-blueschists and their role as a water-budget monitor: a case study from the Hakoishi sub-unit of the Kurosegawa belt, SW Japan

Sato, Eitaro; Hirajima, Tsuyoshi; Yoshida, Kenta; Kamimura, Kenichiro; Fujimoto, Yaoshikazu

doi:10.1127/ejm/2016/0028-2573

Cited by 10 publications

(7 citation statements)

References 52 publications

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“…4a). Similar chemographic relations among Pmp-, Lws-and Ep-bearing mineral equilibria with glaucophane in P-T space have been proposed in the Schreinemakers' net (e.g., Liou et al, 1985;Frey et al, 1991;Sato et al, 2016) and P-T pseudosections (e.g., Zhang et al, 2009;Willner et al, 2016;Tsujimori and Ernst, 2014). The retrograde pumpellyite in the Pmp + Gln + Ep + Chl + Ab assemblage might have been formed by the univariant reaction Gln + Zo + H 2 O = Pmp + Chl + Ab in the NCMASH with excess chlorite, albite, quartz, and H 2 O (Liou et al, 1985;Beiersdorfer and Day, 1995).…”

Section: Stability Field Of Pumpellyite In Blueschist-faciessupporting

confidence: 62%

Retrograde pumpellyite in the Yunotani garnet blueschist of the Omi area, Japan: An update on the cooling path

Shinji

Tsujimori

2019

Journal of Mineralogical and Petrological Sciences

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Retrograde pumpellyite was newly found in garnet blueschist that is Mg-rich equivalent of late Paleozoic retrograde eclogite of the Yunotani Valley in the Omi area, Hida-Gaien Belt. The pumpellyite with high Al/ (Al + Mg + Fe) occurs in pressure shadows around garnets; it is associated with secondary glaucophane, epidote, chlorite, titanite, phengite, albite, and quartz, which all characterize a retrograde blueschist-facies mineral assemblage after peak eclogite-facies mineral assemblage. This feature is comparable with retrograde pumpellyite in late Paleozoic garnet blueschist (with relict eclogite-facies mineral assemblage) in the Osayama area of the Chugoku Mountains. Equilibrium phase calculation confirmed that the pumpellyite is stable at a low temperature and pressure portion of the lawsonite-blueschist-facies. T-bulk-composition (Mg) pseudosection suggests that pumpellyite appears preferentially in high Mg/(Mg + Fe) bulk composition. The limited occurrence of retrograde pumpellyite in the Yunotani garnet blueschist and retrograde eclogite would be explained by Mg-rich bulk compositions. Also, the limited occurrence in pressure shadows around garnets suggests that the fluid trapped in the pressure shadows might have enhanced growth (or precipitation) of pumpellyite. This finding provides a strong evidence that the deeply subducted (eclogite-facies) metabasaltic rocks both in the Hida-Gaien Belt and the Chugoku Mountains were subjected to a very similar blueschist-facies overprinting locally reached the pumpellyite stability field. The 'Franciscan-type' cooling path suggests a 'steady-state' underflow of the paleo-Pacific oceanic plate in late Paleozoic at a convergent margin of the South China Craton.

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Section: Stability Field Of Pumpellyite In Blueschist-faciessupporting

confidence: 62%

Retrograde pumpellyite in the Yunotani garnet blueschist of the Omi area, Japan: An update on the cooling path

Shinji

Tsujimori

2019

Journal of Mineralogical and Petrological Sciences

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“…These assemblages are stable under the pumpellyite-actinolite (PA) or pumpellyite-blueschist (PBS) facies (Banno, 1998;Katzir et al, 2000;Sato et al, 2017). The mineral assemblage lawsonite + phengite + Chl + calcite + Ab + Qz is reported from pelitic schist of the Kebara Formation (Tomiyoshi and Takasu, 2009) and a similar mineral assemblage is reported from pelitic schist of the Sanbagawa metamorphic belt in the Ise area, eastern Kii Peninsula.…”

Section: Geological and Petrological Backgroundmentioning

confidence: 66%

Petrology and possible significance of barroisite–bearing metabasite from the Kebara Formation in NW Kii Peninsula

Kato

Hirajima

2017

Journal of Mineralogical and Petrological Sciences

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We report the new finding of barroisite (Brs)-bearing metabasites within a metabasite layer from the Kebara Formation, a unit exposed between the Sanbagawa and the Chichibu belts in NW Kii Peninsula. The dominant lithotype of the metabasite layer shows pale-green colors and is mainly composed of sodium amphibole, actinolite, pumpellyite and epidote. It is in agreement with reported mineral assemblages in the Kebara Formation which document pumpellyite-actinolite (PA) or pumpellyite-blueschist (PBS) facies conditions (<340°C and 0.8 GPa), and with geothermometry based on the Raman analysis of carbonaceous material from metapelite samples which give peak metamorphic temperatures of 300-340°C. Brs grains are identified from metabasites with dark-green color in the layer, and are closely associated with epidote, chlorite, white mica, albite and quartz, but not with pumpellyite. Brs grains are replaced by sodium amphibole and/or winchite at the rim with a distinct compositional gap. Thermodynamic calculation suggests that the Brs + epidote + chlorite + albite + quartz assemblage is stable at P-T conditions higher than 450°C and 0.4 GPa. The abovementioned data suggest that the Brs-bearing metabasites suffered an early higher temperature (>450°C) metamorphism and then overprinted by PA or PBS facies metamorphism along with the main constituents of the Kebara Formation. In the Besshi area of the Sanbagawa belt, the earlier subducted higher grade rocks are considered to juxtapose to the newly subducted rocks and overprinted retrograde metamorphism during their exhumation stage. Our new finding suggests that the similar phenomenon was took place in the lower grade part of the Sanbagawa belt.

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“…The dehydration process under conditions of the greenschist facies (~350–450°C) is driven mainly by the breakdown of chlorite, which is an important water reservoir in low‐ T metamorphism (e.g. Kuwatani, Okamoto, & Toriumi, ; Sato, Hirajima, Yoshida, Kamimura, & Fujimoto, ). Kuwatani et al.…”

Section: Discussionmentioning

confidence: 99%

“…() performed thermodynamic forward modelling of the dehydration process for mafic rocks, revealing that the water content of mafic rocks was controlled mainly by the modal amount of chlorite under greenschist facies conditions. If the P–T path is cold, dehydrated aqueous fluid would be buffered by growth of other hydrous phases such as lawsonite (Sato et al., ), whereas a warm P–T path causes a significant decrease in bulk H 2 O content (Kuwatani et al., ). However, H 2 O contours (Figure b) indicate that changes from low‐ to high‐grade whole‐rock compositions correspond to increasing whole‐rock H 2 O content, although increasing P–T itself causes some dehydration.…”

Section: Discussionmentioning

confidence: 99%

Progressive evolution of whole‐rock composition during metamorphism revealed by multivariate statistical analyses

Yoshida

Kuwatani

Hirajima

et al. 2017

Journal Metamorphic Geology

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The geochemical evolution of metamorphic rocks during subduction-related metamorphism is described on the basis of multivariate statistical analyses. The studied data set comprises a series of mapped metamorphic rocks collected from the Sanbagawa metamorphic belt in central Shikoku, Japan, where metamorphic conditions range from the pumpellyite-actinolite to epidote-amphibolite facies. Recent progress in computational and information science provides a number of algorithms capable of revealing structures in large data sets. This study applies k-means cluster analysis (KCA) and non-negative matrix factorization (NMF) to a series of metapelites, which is the main lithotype of the Sanbagawa metamorphic belt. KCA describes the structures of the high-dimensional data, while NMF provides end-member decomposition which can be useful for evaluating the spatial distribution of continuous compositional trends. The analysed data set, derived from previously published work, contains 296 samples for which 14 elements (Si, Ti, Al, Fe, Mn, Mg, Ca, Na, K, P, Rb, Sr, Zr and Ba) have been analysed. The KCA and NMF analyses indicate five clusters and four end-members, respectively, successfully explaining compositional variations within the data set. KCA indicates that the chemical compositions of metapelite samples from the western (Besshi) part of the sampled area differ significantly from those in the east (Asemigawa). In the west, clusters show a good correlation with the metamorphic grade. With increasing metamorphic grade, there are decreases in SiO 2 and Na 2 O and increases in other components. However, the compositional change with metamorphic grade is less obvious in the eastern area. End-member decomposition using NMF revealed that the evolutional change of whole-rock composition, as correlated with metamorphic grade, approximates a stoichiometric increase of a garnet-like component in the whole-rock composition, possibly due to the precipitation of garnet and effusion of other components during progressive dehydration. Thermodynamic modelling of the evolution of the whole-rock composition yielded the following results: (1) the whole-rock composition at lower metamorphic grade favours the preferential crystallization of garnet under the conditions of the garnet zone, with biotite becoming stable together with garnet in higher-grade

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Phase relations of lawsonite-blueschists and their role as a water-budget monitor: a case study from the Hakoishi sub-unit of the Kurosegawa belt, SW Japan

Cited by 10 publications

References 52 publications

Retrograde pumpellyite in the Yunotani garnet blueschist of the Omi area, Japan: An update on the cooling path

Retrograde pumpellyite in the Yunotani garnet blueschist of the Omi area, Japan: An update on the cooling path

Petrology and possible significance of barroisite–bearing metabasite from the Kebara Formation in NW Kii Peninsula

Progressive evolution of whole‐rock composition during metamorphism revealed by multivariate statistical analyses

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