Phase equilibria in the granite-H2O-HF system and effect of fluorine on granitic melt structure |
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| Authors: | Xiaolin Xiong Zhenhua Zhao Jinchu Zhu Bing Rao Mingyuan Lai |
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| Institution: | 1. Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, 510640, Guangzhou
2. Department of Earth Sciences, Nanjing University, 210093, Nanjing
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| Abstract: | Experiments carried out in the system granite-H2O-HF at 0.1 GPa show that the crystal-liquid equilibrium temperature of quartz rises and that of alkali-feldspar goes down with increasing F content. The calculated results of quartz and alkali feldspar crystal-liquid equilibrium show that the activity of SiO2 in melt increases and the activities of NaAlSi3O8(Ab) and KAlSi3O8(Or) decrease, with a greater decreasing extent for a Ab L than a Or L . These systematic changes are believed to be caused by F complexing with Al, Na, K, but not Si in the melt, and are consistent with F decomposing AlO 2 ? tetrahedra and more preferentially forming complexes with Na than K. The comparison between effects of F and H2O on phase equilibrium suggests that the maximum difference affecting melt structure between F and OH is F complexing without Si and OH complexing with Si in granitic melt. |
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