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Calibration and Applications of Spinel Equilibria in the System FeO-Al2O3-SiO2 |
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| Authors: | BOHLEN STEVEN R; DOLLASE WAYNE A; WALL VICTOR J |
| Institution: | 1Department of Earth and Space Sciences, The State University of New York Stony Brook, New York 11794 2Department of Earth and Space Sciences, University of California Los Angeles, California 90024 3Department of Earth Sciences, Monash University Clayton, Victoria 3168, Australia |
| Abstract: | A new thermobarometer, based on the equilibrium:
 has been calibrated with experiments carried out in the piston-cylinderapparatus. Reversed equilibria were obtained using well-calibrated2.54 cm NaCl furnace assemblies and Ag80Pd20capsules with fO2bufferedat or near iron-wustite. The equilibrium is located between5.2–5.4, 6.6–6.8, and 8.6–8.8 kb at 880, 940,and 1020?C, respectively, and at 5.2 and 8.8 kb between 865–880and 1020–1030?C, respectively. X-ray refinement data indicate that the hercynite (a = 8.15546?) has approximately 18 per cent inverse character. M?ssbauerspectra reveal that 4 mol per cent of the Fe is ferric (2 percent magnetite component). Broad Mossbauer lines and a Fe2+energy level splitting of 3.7 kJ mol–1 calculated fromthe Mossbauer spectra are consistent with the X-ray determineddegree of inversion, although no separate octahedral Fe2+ spectraldoublet is resolved. Calibration of this equation allows calculation of the equilibrium:
 Thermobarometers based on the above equilibria are widely applicablein granulite fades rocks and yield pressure/temperature datathat are consistent with other well-calibrated barometers andthermometers. |
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