Garnet-biotite geothermometry of a pelitic gneiss from the Lutzow-Holm Complex in Skallen, East Antarctica: Constraints on retrograde metamorphism
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...
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| Format: | Report |
| Language: | English |
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Department of Earth and Planetary Sciences, Graduate School of Science, Kyushu University
2004
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| 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 |
| Summary: | 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. |
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