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Eutectic crystallization in the undercooled orthoclase-quartz-H (sub 2) O system; experiments and simulations

Don R. Baker and Carmela Freda
Eutectic crystallization in the undercooled orthoclase-quartz-H (sub 2) O system; experiments and simulations (in Experimental mineralogy, petrology and geochemistry, Anonymous)
European Journal of Mineralogy (June 2001) 13 (3): 453-466


Textures formed during crystallization of the eutectic composition in the system Orthoclase-Quartz-H (sub 2) O at 500 MPa and 50, 100, and 200 degrees C undercooling have been studied experimentally and simulated using a two-dimensional Ising model. The experiments performed at 50 degrees C undercooling did not produce complex, interesting textures but only very rare, isolated K-feldspar and quartz crystals. At 100 degrees C undercooling the most common texture is a fine-grained, submicrometre to micrometre-scale, spherulitic quartz-K-feldspar intergrowth; set within this intergrowth are larger individual crystals of quartz or K-feldspar. Experiments performed at 200 degrees C undercooling are remarkable for the occurrence of micrometre-scale graphic textures and millimetre scale spherulitic textures, characterized by quartz-K-feldspar intergrowths in the core and dominated by K-feldspar at the rims. Simulations of crystal growth, performed to complement and to interpret the experimental products, investigated what combination of growth (G) and diffusion (D) conditions can give rise to the crystal shapes and textures found in the experiments. These conditions correspond to growth rates between approximately 1 X 10 (super -10) and 5 X 10 (super -9) m s (super -1) and diffusion coefficients between 10-17 m2 s (super -1) in the melt phase and 10-8 m (super 2) s (super -1) in the fluid phase. The simulations, despite their limitations, provide textures similar to the experimental ones. In particular, simulations produced a quartz-K-feldspar intergrowth when G = D and singular, large quartz and K-feldspar crystals when G<D. These changes in the G:D ratio, in the experiments and in natural rocks, are attributed to a change in the growth of the crystal from a silicate melt to an aqueous fluid. The most interesting results of this study are that highly undercooled melts of a simplified pegmatite composition produce textures remarkably similar to natural pegmatites and that simulations provide a powerful tool to understand what processes cause these textures in experimental run products and natural rocks.

ISSN: 0935-1221
EISSN: 1617-4011
Serial Title: European Journal of Mineralogy
Serial Volume: 13
Serial Issue: 3
Title: Eutectic crystallization in the undercooled orthoclase-quartz-H (sub 2) O system; experiments and simulations
Title: Experimental mineralogy, petrology and geochemistry
Author(s): Baker, Don R.Freda, Carmela
Author(s): Anonymous
Affiliation: McGill University, Earth and Planetary Sciences, Montreal, QC, Canada
Pages: 453-466
Published: 200106
Text Language: English
Publisher: Schweizerbart'sche Verlagsbuchhandlung (Naegele u. Obermiller), Stuttgart, Federal Republic of Germany
Meeting name: Eighth international symposium on Experimental mineralogy, petrology and geochemistry
Meeting location: Bergamo, ITA, Italy
Meeting date: 20000416April 16-19, 2000
References: 28
Accession Number: 2001-055191
Categories: Igneous and metamorphic petrology
Document Type: Serial Conference document
Bibliographic Level: Analytic
Illustration Description: illus. incl. 2 tables
Country of Publication: Germany
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute.
Update Code: 200117
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