| Reference Type | Journal (article/letter/editorial) |
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| Title | Metamorphism of the pelitic rocks of the Snyder Group in the contact aureole of the Kiglapait layered intrusion, Labrador: effects of buffering partial pressures of water |
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| Journal | Canadian Journal of Earth Sciences |
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| Authors | Speer, J. Alexander | Author |
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| Year | 1982 (October 1) | Volume | 19 |
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| Issue | 10 |
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| Publisher | Canadian Science Publishing |
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| DOI | doi:10.1139/e82-168Search in ResearchGate |
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| Generate Citation Formats |
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| Mindat Ref. ID | 477265 | Long-form Identifier | mindat:1:5:477265:5 |
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| GUID | 0 |
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| Full Reference | Speer, J. Alexander (1982) Metamorphism of the pelitic rocks of the Snyder Group in the contact aureole of the Kiglapait layered intrusion, Labrador: effects of buffering partial pressures of water. Canadian Journal of Earth Sciences, 19 (10) 1888-1909 doi:10.1139/e82-168 |
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| Plain Text | Speer, J. Alexander (1982) Metamorphism of the pelitic rocks of the Snyder Group in the contact aureole of the Kiglapait layered intrusion, Labrador: effects of buffering partial pressures of water. Canadian Journal of Earth Sciences, 19 (10) 1888-1909 doi:10.1139/e82-168 |
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| In | (1982, October) Canadian Journal of Earth Sciences Vol. 19 (10) Canadian Science Publishing |
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| Abstract/Notes | The petrography and mineral chemistries of the Aphebian Snyder Group pelitic rocks in the contact aureole of the Kiglapait layered intrusion, Labrador reveal a rapid increase in metamorphic grade over 1.7 km from the greenschist facies to the granulite facies. Three zones of metamorphic grade are defined by the aluminum silicates: I, andalusite; II, andalusite + sillimanite; and III, sillimanite. In addition to the succession in the aluminum silicates, progressive metamorphic mineral assemblages, with quartz, K-feldspar, and plagioclase, evolve from chlorite + biotite + muscovite through cordierite + biotite ± muscovite and garnet + cordierite + biotite to orthopyroxene + garnet + cordierite + biotite and eventually either orthopyroxene + cordierite ± biotite or orthopyroxene + garnet + cordierite. Anatectites, believed to be derived from pelitic rocks, intrude as small stocks in zone III. They comprise biotite + cordierite ± garnet ± orthopyroxene monzogranites or granodiorites with accessory ilmenite, rutile, monazite, and dumortierite.The contact metamorphism is isobaric with pressure just above the intersection of the muscovite + quartz decomposition with the andalusite–sillimanite transition. Most published geobarometers place the estimated pressure of metamorphism at 4 ± 1 kbar (400 ± 100 MPa), but use of the lower Holdaway triple point would put it at 2.25 kbar (225 MPa). The temperature ranges from 450 °C in zone I to 900 °C or more adjacent to the Kiglapait intrusion. The range of values of [Formula: see text] is estimated to be 0.1–0.9Ptotal. Because most reactions are dehydration reactions, conditions of [Formula: see text] less than Ptotal allow the metamorphic reactions to buffer the partial pressure of water. This results in the common occurrence of low-variance assemblages and leads to an apparent overlapping of mineral assemblages and mineral chemistries with increasing metamorphic grade. |
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