Prograde and Retrograde Eclogites in the Sambagawa Metamorphic Belt, Besshi District, Japan

Takasu, Akira

doi:10.1093/petrology/25.3.619

Cited by 89 publications

(74 citation statements)

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“…[8] One of the best studied members of the Eclogite unit is the Seba eclogite body [Takasu, 1984;Aoya and Wallis, 1999;Aoya, 2001Aoya, , 2002Zaw Win Ko et al, 2005]. The presence of paragonite during prograde and retrograde conditions shows that peak pressure in at least some members of the Eclogite unit did not exceed 2.3 GPa [Aoya, 2001, Matsumoto et al, 2003.…”

Section: Geological Settingmentioning

confidence: 99%

Structural and petrological constraints on the tectonic evolution of the garnet‐lherzolite facies Higashi‐akaishi peridotite body, Sanbagawa belt, SW Japan

Mizukami

Wallis

2005

Tectonics

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[1] The Higashi-akaishi peridotite body in the Sanbagawa metamorphic belt is a unique example of a kilometer-scale body including garnet-lherzolite facies rocks from an oceanic subduction-type orogen. In this body, four distinct deformational phases D 1 , D 2 , D 3 , and D 4 can be defined. The tectonic significance of D 1 is unclear. Microstructural observations and application of garnet-orthopyroxene geothermobarometry suggest that D 2 took place during high-temperature subduction up to depths of $100 km (from 2.3 GPa to above 2.8 GPa at temperature of 700-800°C) or more. D 3 represents a major phase of exhumation. After exhumation the Higashi-akaishi body became juxtaposed with the adjacent Besshi and Eclogite units at a depth of around 35 km (1 GPa). The common history of the two units after D 3 is shown by the intertectonic growth of tremolite between D 3 and D 4 that corresponds to a stage of intertectonic growth of plagioclase in the Besshi and Eclogite units. Both the spatial distribution and the estimated pressuretemperature (P-T) conditions of this intertectonic phase of mineral growth in the different units are in excellent agreement. The development of an antigorite schistosity during the late stage of D 2 indicates an anticlockwise P-T path with cooling at depths of around 100 km. The association of the antigorite-bearing fabric and the onset of exhumation after the D 2 stage suggest that the density decrease due to antigorite formation may have been sufficient to trigger the exhumation of dense ultramafic body from UHP conditions in subduction zones. Syn-D 2 water introduction and the anticlockwise P-T path are expected when convection in the mantle wedge brings peridotite toward a subduction boundary through mantle wedge or when peridotite is dragged down along a subduction boundary that is progressively cooling immediately after initiation of subduction. Citation: Mizukami, T., and S. R. Wallis (2005), Structural and petrological constraints on the tectonic evolution of the garnet-lherzolite facies Higashi-akaishi peridotite body, Sanbagawa belt, SW Japan, Tectonics, 24, TC6012,

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Section: Geological Settingmentioning

confidence: 99%

Structural and petrological constraints on the tectonic evolution of the garnet‐lherzolite facies Higashi‐akaishi peridotite body, Sanbagawa belt, SW Japan

Mizukami

Wallis

2005

Tectonics

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“…The few known exceptions are from SW Norway (Krogh, 1977;Griffin et al, 1984), New Caledonia (Black, 1977), the Adula Nappe (Heinrich, 1982), and from Venezuela, where Maresch (1983) first reported a field example indicating progressive in-situ dehydration of amphibolite to eclogite. Recently, Takasu (1984) presented textural evidence for the transformation of epidote amphibolite to hydrous eclogite, which he ascribed to prograde dehydration metamorphism.…”

Section: Introductionmentioning

confidence: 99%

Eclogite Facies Regional Metamorphism of Hydrous Mafic Rocks in the Central Alpine Adula Nappe

Heinrich

1986

Journal of Petrology

177

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The Adula Nappe is a slice of Pre-Mesozoic continental basement affected by Early Alpine (Mesozoic or Lower Tertiary) high-pressure metamorphism. Mineral compositions in mafic rocks containing omphacite -I-garnet + quartz record a continuous regional trend of increasing recrystallization temperatures and pressures that can be ascribed to this regional high-pressure metamorphic event. P-T estimates derived from mineral compositions grade from about 12 kb and 500 °C or less in the north of the nappe to more than 20 kb/800 °C in the south.The regional P-T trend is associated with a mineralogical transition from assemblages containing additional albite and abundant amphiboles, epidote minerals, and white micas in the north (omphacite-garnet amphibolites) to kyanite eclogites containing smaller amounts of hornblende and zoisite in the south. Textures and mineral compositional data show that these hydrous and anhydrous silicates associated with omphacite + garnet-I-quartz are primary parts of the high-pressure assemblages. Observed phase relations between these primary silicates, theoretical Schreinemakers analysis, and the thermobarometric results, together indicate that the regional transition from omphacite amphibolites to kyanite eclogites can be described by two simplified reactions: alb + epi + hbl = omp + kya -I-qtz + par (H 2 O-conserving)par + epi + hbl + qtz = omp + kya + H 2 O (dehydration)which have the character of isograd reactions. Local variations of water activity (a H2<3 ) as indicated by isofacial mineral assemblages, and the H 2 O-conserving character of the reaction (15), are interpreted to reflect largely H 2 O-undersaturated and predominantly fluid-absent high-pressure metamorphism within the northern part of the nappe. The omphacite amphibolites and paragonite eclogites in this area are thought to have formed by H 2 O-conserving reactions from Pre-Mesozoic high-grade amphibolites, i.e. from protoliths of similar bulk H 2 O-content.The second 'isograd' (12) is interpreted to mark the regional transition from largely fluid-absent metamorphism in the north to fluid-present metamorphism in the south, where metamorphic pressures and temperatures in excess of 12-15 kb and 500-600 °C were sufficient for prograde in-situ dehydration of similar hydrous protoliths to kyanite eclogites. The observation of abundant veins, filled with quartz + kyanite + omphacite, suggests that a free fluid coexisted locally with the kyanite eclogites of the southern Adula Nappe at some time during progressive dehydration.

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“…The Minawa Formation is composed mainly of pelitic, siliceous, and basic schist. The upper member of the Minawa Formation is composed predominantly of alternating beds of pelitic schist and greenschist, with some ultramafic and metagabbro bodies, including for example the Higashiakaishi peridotite mass, Iratsu epidoteamphibolite mass, and Nikubuchi ultramafic complex (Takasu, 1984b(Takasu, , 1989Kunugiza et al, 1986).…”

Section: Fig 1 (A) Distribution Of the Sambagawa Metamorphic Belt Amentioning

confidence: 99%

Multiple records from osmium, neodymium, and strontium isotope systems of the Nikubuchi ultramafic complex in the Sambagawa metamorphic belt, central Shikoku, Japan

Senda¹,

Kachi²,

Tanaka³

2006

Geochem. J.

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The isotopic compositions of Os, Nd, and Sr, as well as major elements of dunites, spinel lherzolites, websterite, and serpentinite from the Nikubuchi ultramafic cumulous complex in the Sambagawa metamorphic belt (SMB) were investigated. The Nikubuchi ultramafic complex is a layered cumulate and is surrounded by a metagabbro massif in the SMB. We obtained a Sm-Nd whole-rock isochron of the Nikubuchi complex with an age of 138 ± 18 (2σ) Ma and an initial 143 Nd/ 144 Nd ratio of 0.51270 ± 3. The Nikubuchi complex contains well preserved protogranular textures and cumulous layering structures, and has good correlation coefficients among the major element abundances, which indicate an event before the Sambagawa metamorphism. The ε Nd values of 138 Ma (+3.5 to +5.3) correspond to the isotope signatures of ocean island basalt (OIB) or island arc basalt (IAB), and not mid-ocean ridge basalt (MORB). Taking the results of previous studies into consideration, the most likely origin of the Nikubuchi complex is that of a fragmented block of residual cumulate formed by the OIB magma chamber. The Rb-Sr isotope system has been disturbed by hydration and/or metamorphism after 138 Ma, and the Re-Os isotope system also has no valid isochron. One of the possible causes is that rhenium addition by hydration has occurred subsequent to 60 Ma. The results of the isotope systems show that hydration can cause disturbance in Re-Os systems but not in Sm-Nd systems. This probably reflects differences between these systems in resistance of the host phase.

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Prograde and Retrograde Eclogites in the Sambagawa Metamorphic Belt, Besshi District, Japan

Cited by 89 publications

References 0 publications

Structural and petrological constraints on the tectonic evolution of the garnet‐lherzolite facies Higashi‐akaishi peridotite body, Sanbagawa belt, SW Japan

Structural and petrological constraints on the tectonic evolution of the garnet‐lherzolite facies Higashi‐akaishi peridotite body, Sanbagawa belt, SW Japan

Eclogite Facies Regional Metamorphism of Hydrous Mafic Rocks in the Central Alpine Adula Nappe

Multiple records from osmium, neodymium, and strontium isotope systems of the Nikubuchi ultramafic complex in the Sambagawa metamorphic belt, central Shikoku, Japan

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