TEXTURAL DEVELOPMENT OF EXPERIMENTAL GRANITES AS A FUNCTION OF FLUORINE AND COOLING RATES

The presence of volatiles in silicate melts can significantly affect the physical properties of the melt. In addition, slower rates of cooling gradually alter the remaining melt composition, as minerals with higher solidus temperatures crystallize out of solution. The aim in this study is to observe the effect of varying fluorine contents and cooling rates on the texture of the resulting glass. Synthetic gels with consistent weight percentages of orthoclase and variable percentages of quartz, albite, and fluorine were saturated with water and sealed into gold capsules. Three different compositions were studied (0 wt.%, 0.3 wt.%, and 0.8 wt.% fluorine). The capsules were held at 850° C for one day to ensure complete melting and were then lowered to 700° C the following day. The pressure was maintained within 10% of 200 MPa (2 kbar) throughout the entire experiment. One of each of the three composition types was put into three separate cold-seal reaction vessels. The temperature of each was then lowered daily at a constant rate (5°, 10°, and 20° C). Results are forthcoming. It is expected that a difference in texture will be observed between the samples of varying cooling rates and fluorine contents. Results will be studied using the scanning electron microscope, from which images will be acquired using emissions of secondary electrons and x-rays. Previous work by Norris and Wolf (1999) examined the pegmatitic texture of a similar system, which was understaturated with water and had undergone varying cooling rates. GSA1999 abs.w/Prog. 31:62