An experimental study of H solubility in feldspars: Effect of composition, oxygen fugacity, temperature and pressure and implications for crustal processes

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• 作者：Xiaozhi Yang ^{xiaozhi.yang@uni-bayreuth.de}
• 刊名：Geochimica et Cosmochimica Acta
• 出版年：2012
• 出版时间：15 November, 2012
• 年：2012
• 卷：97
• 期：Complete
• 页码：46-57
• 全文大小：883 K

文摘

A series of experiments, with run durations of ¡«100-240 h, have been carried out on H solubility in natural labradorite, albite and anorthoclase at 2-10 kbar and 700-850 ¡ãC, in equilibrium with different oxygen buffer materials: Fe-FeO, Ni-NiO, Re-ReO₂ and Fe₂O₃-Fe₃O₄. Attainment of equilibrium water contents were examined by conducting experiments with different run-durations and by performing profile analysis along crystal core-to-rim paths. The annealed products generally show typical OH-related infrared absorption bands in the range 3700-2600 cm^?1: the spectra of the labradorite and anorthoclase are dominated by broad bands at ¡«3300-3100 cm^?1, while the spectra of the albite consist of broad bands at ¡«3100-3000 cm^?1 and sharp bands at ¡«3600-3400 cm^?1. The measured H solubility, ranging from ¡«80 to 285 ppm H₂O, differs greatly between the feldspars with different chemical compositions, depends strongly on oxygen fugacity, and increases with increasing temperature and pressure. The H solubility is significantly higher, e.g., by a factor of ¡«3 or even more, at very reducing conditions than at oxidizing conditions. The high H solubility of feldspar at reduced conditions indicates that, at least locally, the Earth¡¯s ancient deep continental crust was probably more hydrous than the modern one. Crustal dehydration can be caused by a change of oxygen fugacity and a corresponding change of water solubility in the constituent feldspar under isothermal conditions, without the requirement of high temperature and/or additional heat sources.