Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Abstract Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via ISI Web of Science (5) Citing Articles via Google Scholar Google Scholar Articles by BAKER, D. R. Articles by FREDA, C. Search for Related Content GeoRef GeoRef Citation

Eutectic crystallization in the undercooled Orthoclase-Quartz-H₂O system

¹ Earth and Planetary Sciences, McGill University, 3450 rue University, Montréal, QC H3A 2A7 Canada
² Dipartimento di Scienze della Terra, Università "La Sapienza", P.le A. Moro, 5, I-00185 Roma, Italy

View larger version (123K): [in this window] [in a new window]   Fig. 1. Backscattered electron images of selected experimental products; scale bars in each image are in micrometres. a) Vermicular overgrowth of quartz (dark gray) around seed crystal in quenched melt (light gray) from experiment XLG8 (T 100°C, 25 h). b) Spherulitic texture with larger quartz (black) and K-feldspar crystals (light gray) set in quenched melt (dark gray) and surrounded by spherical vesicles from experiment XLG5 (T 100°C, 50 h). Note crystallization also occurring in corner of capsule at left side of image, c) Enlarged region of same spherulite in XLG5. Note micrometre scale quartz (black)-K-feldspar (light gray) intergrowth set in submicrometre scale intergrowth of the same two minerals, d) Quartz (black)-K-feldspar (light gray) intergrowth from experiment XLG26 (T 100°C, 100 h). Note array of quartz hexagonal cross-sections in lower left-hand corner and the submicrometre scale intergrowth that fills most of the image. Units for scale bars in Fig. 1 and 2 are micrometres. Qtz and Kspar are abbreviations for quartz and K-feldspar crystals. Glass is quenched melt. Circular black regions are vesicles.

View larger version (83K): [in this window] [in a new window]   Fig. 2. a) Millimetre-scale spherulite of quartz (dark gray) and K-feldspar (light gray) growing into vesicles (black) frequently containing subhedral quartz in experiment XLG21 (T 200°C, 50 h). The inner wall of the capsule is just to the left of the field of view of this image and separated from the spherulite by a region of graphically intergrown quartz and K-feldspar. b) Graphic texture from the same experiment (XLG21) enclosed by large K-feldspar crystals containing vesicles partially filled with quartz. Unit for scale bars is micrometres.

View larger version (71K): [in this window] [in a new window]   Fig. 3. Ising model simulations of growth at different ratios of the growth to diffusion probability, or the G:D ratio. In each simulation shown in this work light blue is liquid quartz, dark blue is liquid K-feldspar, yellow is crystalline quartz and red is crystalline K-feldspar. a) G:D ratio = 0.1; 75,000 sweeps; this simulation has been run to completion in order to demonstrate the late-stage enrichment in K-feldspar during crystallization. b) G:D ratio = 1; 60,000 sweeps. c) G:D ratio = 10; 7,000 sweeps.

View larger version (65K): [in this window] [in a new window]   Fig. 4. Growth of a simulated spherulite in which the G:D ratio equals one for the first 20,000 sweeps and is then reduced to 0.1 for the remaining sweeps. Note the fine-grained quartz-K-feldspar intergrowth near the centre, the quartz-enriched zone, and the K-feldspar rich rim. a) 40,000 sweeps. b) 100,000 sweeps. c) 200,000 sweeps.

View larger version (75K): [in this window] [in a new window]   Fig. 5. Ising model simulation of fine-grained spherulite with embedded larger crystals as a function of increasing time (sweeps) from a) to c). Everywhere in this simulation the G:D ratio equals one, except in the region shown by a box where the G:D ratio equals 0.5. a) 400,000 sweeps. b) 600,000 sweeps. c) 800,000 sweeps.

View larger version (17K): [in this window] [in a new window]   Fig. 6. Power-law plot of the comparison of the G:D ratio with average crystal widths normalized to those in simulations with a G:D ratio of 1. Filled circles are Ising Model simulations. Open squares are extrapolations to conditions that yield crystals approximately 100 to 1000 times wider than those produced in simulations with G:D = 1. Brackets encompass estimates of G:D ratios in experiments based upon measured crystal-growth rates and diffusion in either the melt or fluid phase.