Eutectic crystallization in the undercooled Orthoclase-Quartz-H2O system: experiments and simulations
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Bibliographic record
Abstract
Textures formed during crystallization of the eutectic composition in the system Orthoclase-Quartz-H2O at 500 MPa and 50, 100, and 200°C undercooling have been studied experimentally and simulated using a two- dimensional Ising model. The experiments performed at 50°C undercooling did not produce complex, interesting tex- tures but only very rare, isolated K-feldspar and quartz crystals. At 100°C undercooling the most common texture is a fine-grained, submicrometre to micrometre-scale, spherulitic quartz-K-feldspar intergrowth; set within this inter- growth are larger individual crystals of quartz or K-feldspar. Experiments performed at 200°C undercooling are remarkable for the occurrence of micrometre-scale graphic textures and millimetre scale spherulitic textures, charac- terized by quartz-K-feldspar intergrowths in the core and dominated by K-feldspar at the rims. Simulations of crys- tal 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 ~ 1 x 10-10 and 5 x 10-9 m s-1 and diffusion coefficients between 10-17 m2 s-1 in the melt phase and 10-8 m2 s-1 in the fluid phase. The simulations, despite their limitations, provide tex- tures 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 experi- ments 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 composi- tion produce textures remarkably similar to natural pegmatites and that simulations provide a powerful tool to under- stand what processes cause these textures in experimental run products and natural rocks.
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Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
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