On the mechanism of prograde metamorphic reactions in quartz-bearing pelitic rocks

Carmichael, D. M.

doi:10.1007/bf00377479

Cited by 423 publications

(216 citation statements)

References 24 publications

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“…However, this does not mean that A1 was immobile or 'conserved' (e.g. Carmichael, 1969). This reflects the fact that K-feldspar, sodic plagioclase and biotite, or the major minerals in these rocks which contain Al, are all about 20% A1203 in weight.…”

Section: Lsocon Analysis: Resultsmentioning

confidence: 98%

Isocon analysis of migmatization in the Front Range, Colorado, USA

Olsen

Grant

1991

Journal Metamorphic Geology

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Isocon analysis has been applied to five sets of leucosome, mafic selvages and immediately adjacent mesosome in the migmatites from a 15-m outcrop in the Colorado Front Range. The results show: (i) mafic selvages formed from the adjacent mesosome by loss of felsic components and therefore the mesosomes are indeed palaeosomes or protoliths; (ii) the leucosomes did not form in a closed system from the palaeosome (in which case the material lost from the palaeosome during selvage formation would become the leucosome). The observed volumes and compositions of leucosomes require that the present leucosome must contain some material in addition to the felsic components lost from the selvages. The materials that must be added'are leucotonalitic to granitic in composition, varying greatly in K/(Na + Ca)ratio. The trend in leucosome composition can be reproduced by assuming that a metasomatic exchange, K S Na + Ca, modified originally leucotonalitic leucosomes to more K-rich compositions. These leucosomes most likely formed by injection of silicate melts accompanied, or followed, by metasomatism. The trend of leucosome compositions in this study reflects the general trend in the leucosome compositions which have been published from other areas, indicating that the proposed mechanism can be applicable to other regional migmatites.

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Section: Lsocon Analysis: Resultsmentioning

confidence: 98%

Isocon analysis of migmatization in the Front Range, Colorado, USA

Olsen

Grant

1991

Journal Metamorphic Geology

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“…More favourable growth kinetics and faster diffusion rates during deformation may have been responsible for the completion of reaction (4) Ferry, 1983) assuming that alumina was relatively immobile during metamorphism (Carmichael, 1969;Thompson, 1975;Rubie, 1982). The data suggest that deformed samples have been slightly enriched in H 2 O relative to the undeformed samples, and also that K 2 O depletion has occurred (see also coarsening, and the chemical homogenization of the garnet and phengite.…”

Section: Processes Of Formation Of Transition Orthogneissmentioning

confidence: 88%

The Effects of Disequilibrium and Deformation on the Mineralogical Evolution of Quartz Diorite During Metamorphism in the Eclogite Facies

Koons

Rubie

Fruch-Green

1987

Journal of Petrology

108

104

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In the Sesia Zone, Western Alps, a large volume of orthogneiss formed as a result of eclogite fades metamorphism and deformation of quartz diorite during early Alpine underthrusting and subduction. Rare lenses of undeformed metaquartz diorite, preserved within the orthogneiss, represent an early stage in the evolution of this latter rock type. The metamorphic and microstructural evolution of the orthogneiss in the eclogite fades has been reconstructed from studies of gradational contacts between undeformed and strongly deformed rocks.High pressure transformations of the original igneous plagioclase + biotite + quartz assemblage to jadeitic pyroxene (Jd 0 . 95 _ 0 . 83 ) + zoisite + quartz + garnet + 2 muscovites developed prior to deformation. Slow intergranular diffusion resulted in a state of disequilibrium between small textural domains in the metaquartz diorite. The compositions of the phases of the undeformed metaquartz diorite do not reflect the bulk rock composition, but were controlled by their position relative to reactant phases. The jadeitic pyroxenes, for example, formed in localized domains which originally consisted of sodic plagioclase whereas omphacite was the equilibrium pyroxene for the bulk rock composition.Mineralogical changes which occurred during subsequent deformation of the metaquartz diorite are interpreted as resulting from a progressive enlargement of equilibrium domains and the partial equilibration of mineral compositions to the bulk rock composition rather than from changes in pressure and temperature. Initially during high-strain deformation, fine-grained aggregates of jadeitic pyroxene + quartz + zoisite (originally pseudomorphing plagioclase) are inferred to have deformed by a mechanism of grain boundary sliding accommodated by diffusive mass transfer. Muscovite and garnet compositions homogenized during the deformation but due to slow intracrystalline diffusion, pyroxene compositions (Jd o . 9J _ 0 . go ) remained metastable. The coarsening of pyroxene eventually terminated deformation by grain boundary sliding and this mineral subsequently deformed by intracrystalline plastidty. This latter process was accompanied by and perhaps catalysed a change in pyroxene composition from metastable jadeite towards omphacite by a reaction involving the resorption of garnet and the nucleation and growth of paragonite. The resulting orthogneiss consists of quartz -I-omphadte + garnet + phengite + paragonite + zoisite. The rock is characterized by a broad range of pyroxene compositions (Jd o . 8 _ O5 ) due to the incomplete equilibration of this mineral to the bulk rock composition and a lack of Fe-Mg exchange equilibrium between pyroxene and garnet. However, in contrast to the undeformed metaquartz diorite, there are no obvious textural indications of disequilibrium between phases in the orthogneiss.

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“…The biotites that coexist with the zincian staurolite do not have detectable ZnO contents and textures in the rocks do not preclude the possibility that the above reaction occurred as a cycle of coupled reactions as proposed by Carmichael (1969). Alternatively, if Zn was present in the intergranular fluid phase one might reason that the newly formed retrograde staurolite would incorporate Zn.…”

Section: Metamorphic Historymentioning

confidence: 96%

Zincian staurolite in Glen Doll, Scotland

Schumacher

1985

Mineral. mag.

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ABSTRACT. Textures and relict mineralogy in the Dalradian gneisses from the southern contact aureole of the Glen Doll diorite trace the development of three stages of metamorphism through regional and contact metamorphic phases. Regional metamorphic stage I is characterized by the stability of sillimanite+muscovite; recognition of a subsequent regional metamorphic stage II of lower grade is based on textural criteria, the stability of kyanite and staurolite + quartz, and geothermometry/ geobarometry. The breakdown of zincian staurolite occurred under the conditions of contact metamorphism (stage III). Textural evidence from the outer part of the contact aureole suggests that zincian staurolite broke down by the following oxidation reaction: zincian staurolite + muscovite + quartz + O2 andalusite + Zn-rich spinel + magnetite + biotite + H20. Various stages of completion of this reaction have been observed in different parts of a sample. Predominance of magnetite over Zn-rich spinel (~< 14 wt. % ZnO) as a breakdown product can be explained by the initial breakdown of Fe-staurolite component +muscovite+ quartz+O 2 to form andalusite+biotite+magnetite. These product phases were joined by the Zn-rich spinel when sufficient Zn-staurolite component had concentrated in the unreacted staurolite. Rare local examples where Zn-rich spinel is dominant over magnetite may reflect lower O z fugacity and/or higher initial Zn contents of the staurolite.

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On the mechanism of prograde metamorphic reactions in quartz-bearing pelitic rocks

Cited by 423 publications

References 24 publications

Isocon analysis of migmatization in the Front Range, Colorado, USA

Isocon analysis of migmatization in the Front Range, Colorado, USA

The Effects of Disequilibrium and Deformation on the Mineralogical Evolution of Quartz Diorite During Metamorphism in the Eclogite Facies

Zincian staurolite in Glen Doll, Scotland

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