Journal article
Diffusion-controlled olivine corona textures in granitic rocks from Lofoten, Norway; calculation of Onsager diffusion coefficients, thermodynamic modelling and petrological implications
Journal of metamorphic geology, Vol.16(5), pp.607-623
09/1998
DOI: 10.1111/j.1525-1314.1998.00156.x
Abstract
Reactions occurring during cooling of charnockitic intrusives produce characteristic diffusion-controlled textures around fayalite and Fe-Ti oxides. Thermobarometry indicates the corona textures formed at 780-840 degrees C and 4-10 kbar, whereas the magmatic assemblage of the charnockite (clinopyroxene-olivine-quartz) crystallized at approximately 850-870 degrees C and 4 kbar. The succession olivine/orthopyroxene + magnetite/orthopyroxene + garnet and olivine/orthopyroxene + magnetite/amphibole developed where olivine reacted with adjacent plagioclase or K-feldspar, but the modes and the thicknesses of the corona textures vary according to the feldspar type, indicating that the primary magmatic ternary feldspar was already exsolved into albitic plagioclase and alkali feldspar when corona formation began. Simultaneously in other parts of the rock, primary magmatic clinopyroxene reacted to amphibole and Fe-Ti oxides reacted to orthopyroxene + garnet coronas or to amphibole. Textures demonstrate significant Al diffusion in the rocks under granulite-facies conditions and they suggest that no pervasive fluid influx occurred and that amphibole formation was dependent on a local source of H (sub 2) O probably related to water-release during the last stages of magmatism. Calculation of the net reaction by accounting for all observed reactions at different sites in the rock indicates that the system can be regarded as balanced on a hand-specimen scale with respect to all elements except for Na and H (sub 2) O. Relative diffusion coefficients (L (sub i) /L (sub Fe) ) that reproduce the observed textures are: Si 0.82, Mg 0.59, Mn 0.05, Na 0.38, K 0.39, Al 0.05 and Ca 0.07.
Details
- Title: Subtitle
- Diffusion-controlled olivine corona textures in granitic rocks from Lofoten, Norway; calculation of Onsager diffusion coefficients, thermodynamic modelling and petrological implications
- Creators
- G Markl - University of IowaC. T Foster - University of IowaK Bucher - University of Iowa
- Resource Type
- Journal article
- Publication Details
- Journal of metamorphic geology, Vol.16(5), pp.607-623
- Publisher
- Blackwell
- DOI
- 10.1111/j.1525-1314.1998.00156.x
- ISSN
- 0263-4929
- eISSN
- 1525-1314
- Language
- English
- Date published
- 09/1998
- Academic Unit
- Earth and Environmental Sciences
- Record Identifier
- 9984229164402771
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