Chemical variation in micas from the Cairngorm pluton, Scotland
| Autor: | T. N. Harrison |
|---|---|
| Rok vydání: | 1990 |
| Předmět: |
Fractional crystallization (geology)
010504 meteorology & atmospheric sciences Pluton Muscovite Geochemistry Analytical chemistry Electron microprobe engineering.material 010502 geochemistry & geophysics 01 natural sciences Paragonite law.invention Geochemistry and Petrology law engineering Celadonite Crystallization Geology Biotite 0105 earth and related environmental sciences |
| Zdroj: | Mineralogical Magazine. 54:355-366 |
| ISSN: | 1471-8022 0026-461X |
| DOI: | 10.1180/minmag.1990.054.376.01 |
| Popis: | Electron microprobe analyses of micas from the Cairngorm pluton in the Eastern Grampian Highlands of Scotland show extensive compositional variation in biotite, despite a lack of chemical variation in the host granite. Biotite has high Fe/(Fe + Mg) (0.6–0.85) and Alvi (0.6–2.1 a.f.u.), and enrichment trends in these two parameters are attributable to the Al-Tschermak and dioctahedral-trioctahedral substitutions, the latter becoming dominant with increasing Alvi content. Ti content is low (0.2–0.4 a.f.u.), and is largely controlled by a Tschermak-type substitution. Biotite is also unusually rich in Mn (up to 2.57 wt. % MnO), which increases with both Alvi and Fe/(Fe+Mg). F contents generally range between 0.55 and 2.05 wt.% All compositional variation in biotite can be attributed to the extensive development of a fluid phase during the late-magmatic and subsolidus evolution of the pluton. The presence of an abundant fluid phase has resulted in the alteration of biotite to muscovite, which has occurred in response to de-stabilization of the biotite as octahedral R2+ cations are lost in favour of Al. Extreme build-up of this fluid phase has resulted in the crystallization of muscovite as a late, interstitial primary phase. Both primary and replacive muscovite have Fe/(Fe+Mg) > 0.50, 15–36 mol. % celadonite and |
| Databáze: | OpenAIRE |
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