Experimental study of Fe^<3+> solubility in cristobalite and its application to a metamorphosed quartz-magnetite rock from Mt. Riiser-Larsen area, Napier Complex, East Antarctica
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</i>This report concerns the Fe<sup>3+</sup> solubility in cristobalite coexisting with hematite obtained from heating experiments in air at 990-1460 °C in the SiO<sub>2</sub>-Fe<sub>2</sub>O<sub>3</sub> system. The ferric iron substitutes for the tetrahedral silicon in cristobalite and Si<sup>4+</sup> also substitutes for the octahedral Fe<sup>3+</sup> in hematite. Combining the chemical and <i>P-T </i>data of the quartz in the high-pressure eclogite from Sanbagawa belt, central Shikoku, Japan with the present experimental data, we found the content of ferric iron in quartz increases with increasing pressure and temperature:<br><br> ln<i>X</i><sub>Fe</sub> = (−1092 − 5.254<i>T </i>+ 7.75<i>P</i>)/<i>T</i>,<br><br>where <i>X</i><sub>Fe</sub>, <i>T </i>and <i>P </i>are the number of Fe atoms in quartz per formula unit based on a 2-oxygen atom normalization (cationic mole fraction of Fe), temperature in Kelvin and pressure in kbar, respectively. This new geothermometer is applied to the ultrahigh-temperature metamorphosed quartz-magnetite rock from Mt. Riiser-Larsen area, Napier Complex, East Antarctica, resulting that the metamorphic temperatures are estimated as about 994-1095 °C for pressures 5-15 kbar.
- Journal of Mineralogical and Petrological Sciences
Journal of Mineralogical and Petrological Sciences 103(4), 255-265, 2008-08-01
Japan Association of Mineralogical Sciences