Garnet-biotite geothermometry of a pelitic gneiss from the Lutzow-Holm Complex in Skallen, East Antarctica: Constraints on retrograde metamorphism

• Main Author: Takeshi Ikeda
• Format: Report
• Language: English
• Published: Department of Earth and Planetary Sciences, Graduate School of Science, Kyushu University 2004
• Subjects: garnet-biotite geothermometry; retrograde metamorphism; granulite facies; Skallen; Lutzow-Holm Complex; East Antarctica; Antarc*; Antarctica; Polar geoscience
• Online Access: https://nipr.repo.nii.ac.jp/?action=repository_uri&item_id=3136; http://id.nii.ac.jp/1291/00003136/; https://nipr.repo.nii.ac.jp/?action=repository_action_common_download&item_id=3136&item_no=1&attribute_id=18&file_no=1

A garnet-rich pelitic gneiss was examined to estimate retrograde conditions of the Lutzow-Holm Complex in Skallen, East Antarctica. Porphyroblastic grains of garnet show a chemical zoning of an outward decrease in Mg/Fe, and include biotite, plagioclase and quartz. Local depletion in Mg/Fe of garnet is recognized where garnet is in contact with biotite occurring as inclusions and in the matrix. A pair of garnet-biotite geothermometry and garnet-plagioclase-sillimanite-quartz (GASP) geobarometry were applied for garnet rim and matrix biotite that are not in contact with each other, which demonstrates a retrograde condition of 5.6 kbar and 760℃. Pairs of garnet and adjacent biotite yield temperatures of ca. 660℃ at a nominal pressure of 6 kbar irrespective of whether biotiteoCcurs in the matrix or as inclusions, which represents the closure temperature for the exchange reaction between garnet and biotite.