High-pressure and high-temperature experiments on the phase relations in the system of Mg-rich garnet composition (Prp75Alm25): Implication for the Fe-Mg partitioning between garnet and orthopyroxene

• Main Authors: Sato, Kei, Kawasaki, Toshisuke
• Format: Report
• Language: English
• Published: Division of Earth Sciences, Department of Biosphere-Geosphere Sciences, Faculty of Science, Ehime University/Division of Earth Sciences, Department of Biosphere-Geosphere Sciences, Faculty of Science, Ehime University 2002
• Subjects: P-T diagram of the Mg-rich garnet system; Fe-Mg paititioning; geothermometer; ultrahigh-temperature metamorphism; Enderby Land; Polar geoscience
• Online Access: https://nipr.repo.nii.ac.jp/?action=repository_uri&item_id=3109; http://id.nii.ac.jp/1291/00003109/; https://nipr.repo.nii.ac.jp/?action=repository_action_common_download&item_id=3109&item_no=1&attribute_id=18&file_no=1

The phase lelations in the system of Mg-rich garnet composition (P_1p_<75>Alm_<25>) were investigated using a piston cylinder appaiatus at 11-23 kbai and 1000-1300℃ The following mineral assemblages were obtained with decieasing pressure at 1200℃ garnet, garnet + oithopyroxene + sapphinne + quartz, orthopyroxene + sapphmne + quartz At 11 kbar the assemblage of orthopyioxene + sapphirine + quartz changed to that of orthopyroxene + sapphirine + quartz + sillimanite at a certain temperatuie between 1000 and 1100℃ The Fe-Mg distribution coefficients of coexisting garnet and orthopyioxene K_D = (X_<Mg>/X_<〓〓>)^<0p〓>(X_<〓〓>/X_<Mg>)^<cnt> was experimentally determined The new gamet-oithopyroxene geothermometet has been obtained as 7(℃) = (2387±146)/[1nK_D + (1 20±0 10)]-273 We estimated the retrogiade metamoiphic temperatures of UHT metamorphic rocks from Enderby Land East Antaictica as 812-1010℃ Our estimations matched with previous estimations based on Fe-Mg exchange and were about 200-300℃ lowei than those of previous estimations based on feldspai theimometry