Ferriphengite and Aegirinjadeite in a Crystalline Schist of the Iimori District, Kii Peninsula

Kanehira, Keiichiro; Banno, Shohei

doi:10.5575/geosoc.66.654

Cited by 24 publications

(9 citation statements)

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“…Because muscovite may incorporate extensive phengite substitution at low temperatures and high pressures (e.g., Velde, 1965;Massonne and Schreyer, 1987;Bucher-Nurminen, 1987), it seems unlikely that illite would become stable as a result of this substitution. The case of Fe 3 § in illite is similar: muscovite may contain substantial octahedral Fe 3 § substituting for A1 (e.g., Foster, 1956;Kanehira and Banno, 1960). Even though much of the Fe in illite may be Fe 3 § rather than Fe 2 § the similar capacity of muscovite to absorb Fe 3 § implies that this ion is unlikely to stabilize illite over muscovite + pyrophyllite.…”

Section: Metastability Of Illitementioning

confidence: 91%

Transmission Electron Microscopic Study of Coexisting Pyrophyllite and Muscovite: Direct Evidence for the Metastability of Illite

Jiang

Essene

Peacor

1990

Clays and clay miner.

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Abstract--Transmission electron microscopy has been used to characterize coexisting pyrophyllite and muscovite in low-grade metamorphosed pelites from Witwatersrand and northeastern Pennsylvania. The Witwatersrand sample consisted largely of porphyroblasts of interlayered muscovite and pyrophyllite in a fine-grained matrix of the same phases. In both textures, muscovite and pyrophyllite occurred as interlayered packets (with apparently coherent interfaces) from about 300 A to a few micrometers in thickness, with no mixed layering. Their compositions were determined with a scanning transmission electron microscope to be (Do.H KL72NaoA 7)(A13.9 ~ Feo.03Mgo.osTio.01)(Si6.1 ~ All.s9)O20(OH)4 and (D t.90Nao.06Ko.oa)(A13.gaFeo.ot Mgo.os)(SiT.94Alo.06)O20(OH)4, respectively.The pyrophyUite and muscovite in the Pennsylvania shale likewise occurred only as coexisting coherent to sub-parallel packets as thin as 200 ~, with compositions of ([-ql.s9Nao.04Cao.02Ko.05)(A13.93Feo.04Mgo.02Tio.oj)(Si7.92Alo.os)O20(OH)4 and (Nao.o,fao.02K2.03XA13.saFeo.24Mgo.~6Tio.06)(Si6.09Al Lg~)O20(OH),. The textures of both samples were consistent with an equilibrium relationship between pyrophyllite and muscovite. The Pennsylvania sample also contained N H 4 -r i c h illite, kaolinite, and an illite-like phase having intermediate Na/K, which collectively imply non-equilibrated low-grade conditions.The compositions of these coexisting pyrophyllite and muscovite define a solvus with steep limbs and extremely limited solid solution. Illite is a white mica, intermediate in composition between pyrophyllite and muscovite, formed at much lower temperatures than muscovite. These relations show that illite is metastable relative to pyrophyllite + muscovite in all of its diagenetic and low-grade metamorphic occurrences. This further implies that illite precursor phases, such as smectite, are also metastable. The prograde reactions involving smectite, illite, and muscovite are therefore inferred to represent Ostwaldstep-rule-like advances through a series of metastable phases toward the equilibrium states attained in the greenschist facies. "Illite crystallinity" can therefore be a measure of reaction progress, for which temperature is only one of several determining factors.

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Section: Metastability Of Illitementioning

confidence: 91%

Transmission Electron Microscopic Study of Coexisting Pyrophyllite and Muscovite: Direct Evidence for the Metastability of Illite

Jiang

Essene

Peacor

1990

Clays and clay miner.

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“…The metamorphic mineral assemblage of basic and pelitic schists in the Iimori area indicates that the Iimori sulfides underwent high-grade metamorphism up to the epidoteamphibolite facies (Kanehira, 1967;Wang and Maekawa, 1997), corresponding to the albite-biotite zone in the Sanbagawa metamorphic belt of central Shikoku, where metamorphic zones and P-T paths have been studied in detail (e.g., Banno and Sakai, 1989;Otsuki and Banno, 1990;Enami et al, 1994;Aoya, 2001). Enami et al (1994) estimated the peak P-T conditions of the albite-biotite zone to be 520 ± 25°C and 8-9.5 kbar.…”

Section: Re-os Geochemistry and Timing Of Sulfide Depositionmentioning

confidence: 99%

“…The thick basic schist of the Iimori Unit corresponds to the Main Green Schist Member of the Minawa Formation in the Sanbagawa metamorphic belt, central Shikoku, in which there are numerous Besshitype deposits (Kamiyama et al, 1964). The metamorphic mineral assemblage of basic schists around the Iimori deposit is albite + epidote + chlorite + quartz ± glaucophane ± actinolite ± muscovite ± hornblende, corresponding to Zone C of the four metamorphic zones defined by Kanehira (1967), or the garnet zone of Wang and Maekawa (1997), which belongs to the epidote-amphibolite facies or the transition between the glaucophane schist and the epidote-amphibolite facies. Several radiometric ages of metamorphic minerals have been obtained from the Sanbagawa metamorphic belt in the Kii Peninsula.…”

Section: Geological Backgroundmentioning

confidence: 99%

Re–Os geochronology of the Iimori Besshi-type massive sulfide deposit in the Sanbagawa metamorphic belt, Japan

Nozaki

Kato

Suzuki

2010

Geochimica et Cosmochimica Acta

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“…These include the Franciscan Complex of California (Dickinson, 1971). the Sanbagawa belt of Japan (Kanehira, 1967); the Pelona-Orocopia schist belt, California (Jacobson, 1983) and the Haast schist belt of New Zealand ( B . L. Wood.…”

Section: Tectonic Environment : Sub Duction-accr Etlon Modelmentioning

confidence: 99%

Petrogenesis of metamorphic rocks within a subduction‐accretion terrane, Signy Island, South Orkney Islands

Storey

Meneilly

1985

Journal Metamorphic Geology

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Whole-rock and mineral analyses of polydeformed mica-schist, quartzite, marble and amphibolite are presented from Signy Island, South Orkney Islands, part of the Scotia metamorphic complex. Whole-rock chemistry suggests that the amphibolites are the metamorphosed equivalent ofenriched tholeiitic and alkali basalts of an oceanic intraplate basalt series.These, together with limestones and Mn-rich cherts of an oceanic island assemblage were tectonically mixed with trench or trench inner slope basin sediments in a subduction zone environment. Variation in mineral chemistry indicates an increase in temperature and decrease in pressure during metamorphism; pressures of 8 kbar and temperatures of approximately 545°C were reached during amphibolite facies metamorphism in the latter stages of deformation. These new data provide good evidence to support the previous interpretation of the Scotia metamorphic complex as a subduction complex.

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Ferriphengite and Aegirinjadeite in a Crystalline Schist of the Iimori District, Kii Peninsula

Cited by 24 publications

References 0 publications

Transmission Electron Microscopic Study of Coexisting Pyrophyllite and Muscovite: Direct Evidence for the Metastability of Illite

Transmission Electron Microscopic Study of Coexisting Pyrophyllite and Muscovite: Direct Evidence for the Metastability of Illite

Re–Os geochronology of the Iimori Besshi-type massive sulfide deposit in the Sanbagawa metamorphic belt, Japan

Petrogenesis of metamorphic rocks within a subduction‐accretion terrane, Signy Island, South Orkney Islands

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