AN EXPERIMENTAL STUDY OF Fe-Mg PARTITIONINGS BETWEEN ORTHOPYROXENE AND CORDIERITE IN THE Mg-RICH PORTION OF THE Mg_3Al_2Si_3O_<12>-Fe_3Al_2Si_3O_<12> SYSTEM AT ATMOSPHERIC PRESSURE : CALIBRATION OF ITS GEOTHERMOMETRY FOR HIGH-TEMPERATURE GRANULITES AND IGNEOUS ROCKS

• Main Authors: サカイ サトシ, カワサキ トシスケ, Satoshi SAKAI, Toshisuke KAWASAKI
• Format: Report
• Language: English
• Published: Division of Earth Sciences, Department of Biosphere and Geosphere Sciences, Faculty of Science, Ehime University 1997
• Subjects: orthopyroxene; cordierite; Fe-Mg partitioning; geothermometer; granulite; Antarctic; Antarc*
• Online Access: https://nipr.repo.nii.ac.jp/?action=repository_uri&item_id=2852; http://id.nii.ac.jp/1291/00002852/; https://nipr.repo.nii.ac.jp/?action=repository_action_common_download&item_id=2852&item_no=1&attribute_id=18&file_no=1

Exchange reactions of Fe^<2+> and Mg^<2+> between orthopyroxene and cordierite (abbreviated to Opx and Crd, respectively) : [chemical formula] were experimentally investigated in the Mg-rich portion of the pyrope (Mg_3Al_2Si_3O_<12>)-almandine (Fe_3Al_2Si_3O_<12>) system at temperatures from 1000℃ to 1325℃ under atmospheric pressure. Combining the volume data, the distribution coefficient of Fe-Mg partitionings between these phases, K_D(=[numerical formula]), was formulated as ln K_D=(1424+7.02P)/T-0.619,where P and T are in kbar and K. This reaction is temperature-dependent and would be a useful geothermometer. The applications of this orthopyroxene-cordierite thermometer to some Antarctic granulites yield equilibration temperatures of 100℃-200℃ lower than the previous estimations. This suggests that the exchange reaction of Fe^<2+> and Mg^<2+> between orthopyroxene and cordierite continued down to closure temperatures of 500℃-600℃ caused by subsequent cooling after the peak of metamorphism. Temperature estimations using the present orthopyroxene-cordierite thermometer for the igneous suites including S-type tonalite, rhyolite and granulitic xenoliths in andesite are in good agreement with those obtained from other thermometers.