Geothermobarometry of Precambrian metamorphic rocks from the Tobacco Root Mountains of southwestern Montana
- Univ. of Akron, OH (United States). Dept. of Geology
Upper amphibolite facies metamorphic rocks of Precambrian age, located in the Spuhler Peak area of the Tobacco Root Mountains of southwestern Montana, provide the basis for comparative geothermobarometry. Twenty three samples were chosen for microprobe analyses from a stratified sequence of metapelites interlayered with amphibole schists and gneisses exposed in a cirque headwall (less than one square mile sampling area). The garnet-biotite geothermometry of Indares and Martignole (1985), for three metapelite samples, indicates an average temperature 710 [+-] 35 C at a pressure of 6,530 bars (one sample) using the modified GASP geobarometer of Newton and Haselton (1981). Geothermobarometry on the amphibole schist and gneiss samples using the hornblende-plagioclase geothermometer of Blundy and Holland (1990), for twenty samples, indicates an average temperature of 751 [+-] 47 C. The hornblende-garnet geothermometer of Graham and Powell (1984), for fifteen samples, indicates an average temperature of 628 [+-] 59 C. The total aluminum content of hornblendes from nineteen samples indicates an average pressure of 4,826 [+-] 682 bars (Johnson and Rutherford, 1988) and 6,182 [+-] 793 bars (Blundy and Holland, 1990). Variation of temperature and pressure may be explained by closure temperatures for element exchange between the minerals used in the various geothermobarometers.
- OSTI ID:
- 7140931
- Report Number(s):
- CONF-9404217-; CODEN: GAAPBC
- Journal Information:
- Geological Society of America, Abstracts with Programs; (United States), Vol. 26:5; Conference: 27. annual conference of the North-Central Section of the Geological Society of America (GSA), Kalamazoo, MI (United States), 28-29 Apr 1994; ISSN 0016-7592
- Country of Publication:
- United States
- Language:
- English
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