Phengite geobarometry based on the limiting assemblage with K-feldspar, phlogopite, and quartz

Massonne, H.-J.; Schreyer, Werner

doi:10.1007/bf00375235

Cited by 877 publications

(626 citation statements)

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“…The average Si content of Ms of this first generation (3.14 apfu) indicates, according to the Massone & Schreyer (1987) diagram (Fig. 14B), pressures of ~4 kbar at 450°C, which contrast with previous estimates (11-13 kbar), deduced from the maximum Si content (3.33 apfu) and assuming temperatures of 650°C.…”

Section: Genesis Of Ammonium-rich Mica and Exsolution Lamellaecontrasting

confidence: 80%

“…The two parameters, x and y, allow one to estimate the approximate temperature of formation of a K-rich mica belonging to this chemical system. The influence of increasing pressure on the stability fields cannot be directly deduced from this diagram, although some approximations can be made using, in addition, the geobarometer of Massone & Schreyer (1987). Ferraris et al (2001) described exsolved lamellae of phlogopite in muscovite from a pegmatite of the central Alps.…”

Section: Background Informationmentioning

confidence: 99%

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Exsolution Microstructures in Nh4-Bearing Muscovite and Annite in Gneisses From the Torrox Area, Betic Cordillera, Spain

Cruz¹,

Galdeano²

2009

The Canadian Mineralogist

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Variably sized lamellae of annite within muscovite crystals and lamellae of muscovite within annite crystals from gneissic rocks of the Torrox area in the Betic Cordillera, Spain, are interpreted as formed by exsolution of NH 4 -bearing micas present in the earliest metamorphic assemblage. The NH 4 -rich white mica, identified only in the overlying schists, was formed during the first diagenetic-to-metamorphic episode, with N derived from the maturation of organic matter. Initially contained in white mica, the NH 4 was redistributed between white mica and annite, probably at conditions of increasing metamorphism. In the current assemblage of gneisses, NH 4 is preferentially concentrated in annite, especially in the composite Ms+Ann grains. This assemblage, which consists of muscovite in homogeneous grains + muscovite in exsolved grains + annite in homogeneous grains + annite in exsolved grains, was probably derived from the lower-temperature four-mica assemblage: muscovite + NH 4 -rich white mica + annite + NH 4 -bearing annite. Exsolution as temperature increased explains the presence of NH 4 -rich micas in the overlying schists and the presence of exsolved grains in gneisses. The exsolution process occurred at ~450°C and ~3 kbar, physical conditions characterizing the first metamorphic episode affecting this formation.Keywords: ammonium-rich mica, annite, Betic Cordillera, exsolution, muscovite, phengite, Spain. soMMaire Nous interprétons la présence de lamelles d'annite de tailles différentes dans les cristaux de muscovite, et les lamelles de muscovite au sein des cristaux d'annite, dans les roches gneissiques de la région de Torrox, Cordillères Bétiques, en Espagne, en termes d'une exsolution de micas contenant NH 4 présents dans l'assemblage métamorphique précoce. Le mica blanc enrichi en NH 4 , identifié uniquement dans les schistes de la séquence supérieure, a été formé au cours du premier épisode de recristallisation diagénétique à métamorphique, l'azote ayant été dérivé par maturation de la matière organique. Quoique initialement incorporé dans le mica blanc, le NH 4 fut redistribué entre mica blanc et annite probablement lors d'une augmentation du degré de métamorphisme. Dans l'assemblage actuel des gneiss, le NH 4 est de préférence incorporé dans l'annite, et surtout dans les grains composites à Ms + Ann. Cet assemblage, qui contient la muscovite en grains homogènes + la muscovite en grains exsolvés + l'annite en grains homogènes + l'annite en grains exsolvés, a probablement été dérivé à partir de l'assemblage à quatre micas stables à faible température: muscovite + mica blanc enrichi en NH 4 + annite + annite enrichie en NH 4 . Une exsolution à mesure que la température a augmenté expliquerait la présence de micas riches en NH 4 dans les schistes de la séquence supérieure et la présence de grains exsolvés dans les gneiss. Le processus d'exsolution a eu lieu à environ 450°C et 3 kbar, conditions qui ont caractérisé le premier épisode métamorphique affectant cette formation.(Traduit par la Réda...

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Section: Genesis Of Ammonium-rich Mica and Exsolution Lamellaecontrasting

confidence: 80%

Section: Background Informationmentioning

confidence: 99%

Exsolution Microstructures in Nh4-Bearing Muscovite and Annite in Gneisses From the Torrox Area, Betic Cordillera, Spain

Cruz¹,

Galdeano²

2009

The Canadian Mineralogist

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“…(mean at ∼3.31 a.p.f.u.). Using Massonne and Schreyer's (1987) Phe geobarometer, we conclude that the country rock of the Bixiling Complex underwent rapid decompression from eclogite facies ( a.p.f.u. ; kbar; ЊC) Si p 3.4 P ≈ 13-12 T ≈ 600 toward Ab-Ep amphibolite facies (mean Si p 3.31 a.p.f.u.…”

Section: Discussionmentioning

confidence: 97%

Multichronometric Evidence for an In Situ Origin of the Ultrahigh‐Pressure Metamorphic Terrane of Dabieshan, China

Chavagnac

Jahn²,

Villa

et al. 2001

The Journal of Geology

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A B S T R A C TU-Pb zircon data on gneisses indicate a Late Proterozoic protolith at ∼700 Ma at Bixiling and a Late Archean to Early Proterozoic for the Shuanghe sheet within the ultrahigh-pressure metamorphic terrane of Dabieshan (China). U-Pb zircon and Sm-Nd dates on the gneisses of the Shuanghe sheet constrain a metamorphic peak at ∼230 Ma. Rb-Sr and 40 Ar-39 Ar analyses of phengite from five gneisses in the Bixiling Complex yield ages at 198-212 Ma, overlapping the 190-220-Ma age on eclogites. The host gneisses record a similar metamorphic evolution as the coesite-bearing eclogites since both the peak and the retrograde evolution were contemporaneous. This argues for an in situ tectonic relationship.

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“…The peak metamorphic conditions of the blueschists exposed in the Mudanjiang and Yilan areas were suggested as T = 350 -450 °C on the basis of the temperature range of the epidote -blueschist facies conditions and P = 6 -7 kbar using the b 0 values of phengites (Bai et al, 1988); however, the estimation of pressure by the b 0 value of phengite is unreliable (Massonne and Schreyer, 1987). Recently, Li et al (2009) reported blueschists exposed in the Yilan area that consist of glaucophane, phengite, epidote, albite, chlorite, titanite, and quartz.…”

Section: Introductionmentioning

confidence: 99%

Newly discovered garnet-barroisite schists from the Heilongjiang Complex in the Jiamusi Massif, northeastern China

Liu

Takasu

Liu

et al. 2010

Journal of Mineralogical and Petrological Sciences

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Newly found garnet -barroisite schists from the Heilongjiang Complex in the Yilan area, northeastern China, are petrographically described. They are composed mainly of albite, amphibole, phengite, epidote, garnet, quartz, titanite and magnetite, with minor amounts of stilpnomelane, apatite, hematite, rutile, and ilmenite. The metamorphism of the garnet -barroisite schists are divided into three stages: pre -peak stage of the epidote -blueschist facies; peak stage of the epidote -amphibolite facies (T = 500 -540 °C and P = 10 -12 kbar); and retrograde stage of the greenschist facies. These results reveal a clockwise high -P/T path for the garnet -barroisite schists in the Heilongjiang Complex.

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Phengite geobarometry based on the limiting assemblage with K-feldspar, phlogopite, and quartz

Cited by 877 publications

References 32 publications

Exsolution Microstructures in Nh4-Bearing Muscovite and Annite in Gneisses From the Torrox Area, Betic Cordillera, Spain

Exsolution Microstructures in Nh4-Bearing Muscovite and Annite in Gneisses From the Torrox Area, Betic Cordillera, Spain

Multichronometric Evidence for an In Situ Origin of the Ultrahigh‐Pressure Metamorphic Terrane of Dabieshan, China

Newly discovered garnet-barroisite schists from the Heilongjiang Complex in the Jiamusi Massif, northeastern China

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