Growth history of garnet in pelitic schists of the Sanbagawa metamorphic terrain in central Shikoku

Sakai, Chihiro; Banno, Shohei; Toriumi, Mitsuhiro; Higashino, Toshio

doi:10.1016/0024-4937(85)90012-x

Cited by 45 publications

(31 citation statements)

References 25 publications

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“…The zonal structure of garnet in the Asemi -gawa region has been investigated by Itaya (1978), Sakai et al (1985), Banno et al (1986), andInui (2010). These studies show that most of garnet grains in metapelites exhibit a bellshaped profile of Mn, suggesting a continuous growth of garnet during the prograde stage.…”

Section: Discussionmentioning

confidence: 99%

“…Although highpressure metamorphic rocks were affected to varying degrees by an overprint of hydration crystallization during exhumation and in many circumstances peak mineral assemblages were obliterated, they have however been preserved as inclusions in refractory minerals such as garnet and zircon. The metamorphic P -T history is also well preserved in the form of the compositional zoning of garnet (Sakai et al, 1985). Studies of inclusions therefore enable an understanding of the metamorphic characteristics of the prograde stage, even in extensively retrogressed HP (high -pressure) -UHP (ultra high -pressure) metamorphic rocks (e.g., Sobolev et al, 1995;Katayama et al, 2000), and a combination of the analysis of compositional zoning and of inclusions of garnet is key to deciphering the evolution of the metamorphic belt.…”

Section: Introductionmentioning

confidence: 99%

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Compositional zoning and inclusions of garnet in Sanbagawa metapelites from the Asemi-gawa route, central Shikoku, Japan

Taguchi

Enami

2014

Journal of Mineralogical and Petrological Sciences

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Compositional and textural characteristics of the zonal structure and inclusions of garnet in metapelites from areas of high -grade greenschist facies (garnet zone) to areas of epidote -amphibolite facies (albite -biotite and oligoclase biotite zones) located along the Asemi -gawa route were examined using EPMA and Raman spectroscopy to investigate evolution of the P -T history of Sanbagawa metamorphism. Garnet grains exhibit two types of compositional zoning patterns: bell -shaped and composite types with spessartine variation. Bell -shape zoning is characterized by a monotonous decrease in the spessartine component from the crystal core towards the margin. Almandine and pyrope components exhibit the opposite trend. The grossular content reaches a maximum at an intermediate position between the core and the rim, and then decreases towards the outermost rim. The composite -zoned garnet is divided into core and mantle parts and it exhibits discontinuous compositional variations according to the associated boundary, evidencing resorption of the core and overgrowth of the mantle during crystallization; implying a two -stage growth of garnet during the Sanbagawa metamorphism. Composite -zoned garnet is characteristically observed in metapelites from a part of the albite -biotite zone, and quartz grains included in its core retain a higher residual pressure than those in garnet from other mineral zones. Isolated paragonite crystal occurs particularly as an inclusion in the core part of this composite -zoned garnet. These data suggest that part of the Sanbagawa metamorphic rocks in the Asemi -gawa region recrystallized under higherpressure conditions up to the eclogite facies, prior to regional metamorphism from the greenschist, to the epidote -amphibolite facies that formed the regional thermal structure of the Sanbagawa belt of central Shikoku.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Compositional zoning and inclusions of garnet in Sanbagawa metapelites from the Asemi-gawa route, central Shikoku, Japan

Taguchi

Enami

2014

Journal of Mineralogical and Petrological Sciences

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“…For example, evidence that single crystals have grown at different rates in different directions was presented by, Sakai et al (1985), Spear & Daniel (2001) and Yang & Rivers (2001), and evidence that different crystals in a single population grew at different rates was presented by Finlay & Kerr (1987). The preferred nucleation of garnet crystals on hinges to crenulations was described by Williams (1994) and Spear & Daniel (2001), and conspicuous clusters of garnet crystals were described by Kamineni (1978) and Spiess et al (2001).…”

Section: The Diversity Of Naturementioning

confidence: 99%

Shape, size, spatial distribution and composition of garnet crystals in highly deformed gneiss of the Otter Lake area, Québec, and a model for garnet crystallization

Kretz¹

2006

Journal Metamorphic Geology

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Garnet-biotite-(sillimanite) gneiss ($700°C, 7 kbar) of the Otter Lake area in the Western Grenville Province (Canadian Shield) occurs as granitic gneiss (group 4) that forms a large part of the Otter Complex, and as widely distributed, more heterogenous metasedimentary gneiss (group 2). In one sample of group 4 gneiss (Qtz 25 Pl 34 Kfs 28 Bt 10 Grt 2.5 Sil 1 ) the true diameter (determined by serial grinding) of subhedral garnet crystals ranges from 0.2 to 3.0 mm, with a mode at 1.0 mm. Nearestneighbour measurements in this sample, and in surfaces of nine additional samples (all <5% garnet) confirm that garnet crystals are distributed mainly at random; slight clustering was detected in two samples. In one sample of group 4 gneiss, microprobe analyses on sections through crystal centres (obtained by serial slicing), reveal that small crystals and margins to large crystals contain more Fe and Mn and less Mg than the broad central regions of large crystals. Based on these and previous results, together with theoretical considerations, a crystallization model is proposed, in which, (i) garnet was produced by the continuous reaction, Ms + Bt + Qtz fi Grt + Kfs + H 2 O, (ii) nucleation occurred by the random selection of randomly distributed Ms-Bt-Qtz triple junctions, (iii) the rate of linear growth remained constant, and (iv) as temperature increased, the rate of nucleation first increased slowly, then remained nearly constant, and finally declined. Within-population compositional homogenization was followed, on cooling, by local Fe-Mg-Mn exchange with biotite.

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“…It is possible that some of the investigated garnets have been misidentified in previous studies. For instance, Sakai et al (1985) reported garnet grains which were clustered in the muscovite layers or included in the albite porphyroblasts in the pelitic schists of central Shikoku. Sakai et al discussed the history of grain growth by assuming that the grains originate from proper prograde garnet formed during the Sanbagawa metamorphism and that no other prograde garnet exists in this region.…”

Section: Implication Of Type -B Garnetmentioning

confidence: 99%

Two types of garnet in Sanbagawa pelitic schists along Asemigawa River, central Shikoku

Inui

2010

Journal of Mineralogical and Petrological Sciences

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The mode of occurrence of garnet in pelitic schists of the Sanbagawa metamorphic belt along the Asemigara River in central Shikoku is examined. Two different types of garnets, A and B, are identified from the albite -biotite and the oligoclase -biotite zones of the Sanbagawa belt. Type -A garnets are larger than type -B garnets and show concentric normal chemical zoning. There is no evidence of disequilibrium crystal growth in type -A garnets. On the contrary, type -B garnets are small, and some of them occasionally show sector zoning, which is a strong evidence for a disequilibrium crystal growth. The chemical trend observed between the core and the rim of type -B garnets is different from that observed in the case of type -A garnets, although only some of the type -B garnets show chemical sector zoning. Type -B garnets are typically found in clusters in muscovite -rich layers or are included in albite porphyroblasts. These two types of garnets can be distinguished from each other on the basis of grain size, cluster formation, and chemical composition. Type -B grains are found only in the structurally lower part of the oligoclase -biotite zone and in the lower albite -biotite zone. These two types of garnets are thought to represent two stages of garnet growth. Further, in the case of type -A garnets (early garnet), chemical equilibrium is maintained during prograde metamorphism, and hence, these garnets are suitable for the use in thermobarometric studies.

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Growth history of garnet in pelitic schists of the Sanbagawa metamorphic terrain in central Shikoku

Cited by 45 publications

References 25 publications

Compositional zoning and inclusions of garnet in Sanbagawa metapelites from the Asemi-gawa route, central Shikoku, Japan

Compositional zoning and inclusions of garnet in Sanbagawa metapelites from the Asemi-gawa route, central Shikoku, Japan

Shape, size, spatial distribution and composition of garnet crystals in highly deformed gneiss of the Otter Lake area, Québec, and a model for garnet crystallization

Two types of garnet in Sanbagawa pelitic schists along Asemigawa River, central Shikoku

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