Mixing properties of NaAlSi/sub 3/O/sub 8/ melt-H/sub 2/O: new calorimetric data and some geological implications
The authors present the results of direct calorimetric determinations of the heat of mixing of NaAlSi/sub 3/O/sub 8/ and H/sub 2/O to form hydrous melts and glasses. ..delta..H is small and exothermic throughout the P-T range investigated. At 298 K and 1 bar there is a minimum in ..delta..H (-2.39 kcal/mole at X/sub w//sup m/ approx. = 0.27). Results of high-pressure drop calorimetry on hydrous albite melts show that ..delta..H becomes more endothermic as T increases. The minimum in ..delta..H as a function of X/sub w//sup m/ occurs in the compositional region where OH/sup -/ is the dominant hydrogen-bearing species in the glass. The average partial molal heat capacity of H/sub 2/O in hydrous albite melt (from 298 to 1306 K, 20 cal/mole/K) is similar to that of pure liquid water at ambient conditions. Reconnaissance studies in the system 4Q-Ab-Or-H/sub 2/O indicate a general similarity with the Ab-H/sub 2/O system in that ..delta..H is small and exothermic. In detail, however, Ab-H/sub 2/O provides neither a quantitative nor a qualitative model for the more complex haplogranite melts. At 298 K, ..delta..H for the studied haplogranite composition is at a minimum of -0.75 kcal/mole at X/sub w//sup m/ approx. = 0.5. Their results help to explain geological phenomena such as the high water contents of perlitic obsidians and the lack of thermal magma quenching accompanying exsolution of dissolved water in explosive volcanic eruptions.
- Research Organization:
- Arizona State Univ., Tempe
- DOE Contract Number:
- AC02-80ER10765
- OSTI ID:
- 5749038
- Journal Information:
- J. Geol.; (United States), Vol. 95:2
- Country of Publication:
- United States
- Language:
- English
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ALUMINIUM SILICATES
MIXING HEAT
SODIUM SILICATES
CALORIMETRY
GLASS
HYDROTHERMAL SYSTEMS
MAGMA
PRESSURE DEPENDENCE
ROCK-FLUID INTERACTIONS
TEMPERATURE DEPENDENCE
VOLCANISM
WATER
ALKALI METAL COMPOUNDS
ALUMINIUM COMPOUNDS
ENERGY SYSTEMS
ENTHALPY
GEOTHERMAL SYSTEMS
HYDROGEN COMPOUNDS
OXYGEN COMPOUNDS
PHYSICAL PROPERTIES
SILICATES
SILICON COMPOUNDS
SODIUM COMPOUNDS
THERMODYNAMIC PROPERTIES
152000* - Geothermal Data & Theory