Depth to and concentrations of water in large bodies of silicic magma. Technical progress report
Large bodies of silicic magma are potential sources of geothermal energy and ore. They also pose threats of catastrophic eruptions. The depths of such bodies are related to their economic potential and probably to their eruption mechanisms. The concentrations of water in the magmas are important for their eruptive and dynamical behavior and for the development of ores. The concentration of water in melt before ascent and eruption can be measured in inclusions of glass which became trapped in crystals before extrusion. The depth of a magma body can be estimated or delimited if we can find out the concentrations of both carbon dioxide and water in the inclusions of glass. Initial results on the Bishop Tuff of Long Valley Caldera, California yield 4.9 +- 0.5 percent H/sub 2/O for glass included in quartz from the Plinian air fall pumice. We estimate a minimum pressure of about 1.3 kb +- 0.2 kb at the top of the body of magma before eruption. Petrographical work on both the Bishop Tuff and the Upper and Lower Bandelier Tuffs of Valles Caldera, New Mexico, suggest that at least the upper parts of all these bodies of silicic magma were saturated with a gas. However, all of the inclusions are devitrified which we find in quartz phenocrysts from even quickly cooled, glassy equivalents of the ignimbritic parts of the tuffs. We do not understand the cause of the devitrification and consider it important to investigate further because of possible significance for the eruption and emplacement mechanisms of ignimbrites, and because inclusions revitrified by laboratory heating may nevertheless yield significant information.
- Research Organization:
- Chicago Univ., IL (USA). Dept. of Geophysical Sciences
- DOE Contract Number:
- AC02-80ER10763
- OSTI ID:
- 5170912
- Report Number(s):
- DOE/ER/10763-1; ON: DE82012936
- Country of Publication:
- United States
- Language:
- English
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