| Abstrakt: |
Quartz is an important mineral constituent of the continental crust, which commonly contains trace amounts of water as hydroxyl in the lattice. Despite considerable efforts to document the roles of pressure, temperature, and chemistry on water storage in quartz, the effect of redox state, a key thermodynamic factor in Earth sciences, has not been well established. We assessed the redox effect on water solubility in quartz at 2 and 10 kbar and 800°C, by equilibrating two natural gem‐quality crystals with water over a range of redox conditions. Recovered samples show infrared absorption bands at 3,100–3,600 cm−1. Dehydration experiments at 1200°C (room pressure) suggest that the two bands at ∼3,197 and 3,293 cm−1 are linked to Si‐O overtones, with the other bands to hydroxyl. The water solubility, ∼3.7–32.2 ppm wt. H2O, is redox‐independent, differing from other minerals such as feldspar, pyroxenes, garnet, rutile, and olivine in which the water solubility is significantly redox‐dependent. This provides evidence that the water incorporation in quartz is not controlled by polyvalent elements and/or other redox‐linked mechanisms. Considering the roles of Al, Li, and B in incorporating water and its low solubility over remarkable variations in the abundances of those elements in most natural samples, quartz is not a major water carrier compared to other nominally anhydrous minerals (NAMs) in the crust. The partitioning of water between quartz and other crustal NAMs such as feldspar, pyroxenes, rutile, and garnet is redox‐influenced, and is unlikely to be constant in the crust. Plain Language Summary: Water occurs commonly in the form of hydroxyl groups in quartz, the second most abundant mineral in the continental crust, and affects many physicochemical properties of the host mineral. However, the storage of water in quartz has not been studied as a function of oxygen fugacity, a critical thermodynamic parameter for describing Earth's redox state. We measured the water solubility in quartz by experimental studies at high pressure and high temperature over a wide range of redox conditions. We show that the solubility of water is redox insensitive. This suggests that the incorporation of water is unlikely to be controlled by polyvalent elements such as Fe and/or other redox‐involved mechanisms. Amongst the various nominally anhydrous minerals (NAMs) in the crust including feldspar, pyroxenes, garnet, and rutile, quartz is unlikely to be a major water carrier due to its low water solubility. The highly contrasting redox effects on the solubility of water between quartz and other nominally anhydrous crustal minerals indicate that the water partitioning between them is strongly redox‐dependent. The results of this study are important for understanding the incorporation mechanism of water in quartz and its chemical and physical effects. Key Points: An experimental study of water solubility in quartz under well‐controlled pressure, temperature, and redox conditionsRedox‐insensitive water solubility in quartz implies H substitutions not controlled by polyvalent elements or other redox‐linked mechanismsThe low water solubility of quartz rules out its role as a major water carrier among nominally anhydrous minerals in the continental crust [ABSTRACT FROM AUTHOR] |
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