New evidence for prograde metamorphism and partial melting of Mg-Al-rich granulites from western Namaqualand, South Africa

• Main Authors: Yoshikuni Hiroi, Tomokazu Hokada, Masaaki Beppu, Yoichi Motoyoshi, Toshiaki Shimura, Masaki Yuhara, Kazuyuki Shiraishi, Geoffrey H. Grantham, Mike W. Knoper
• Format: Report
• Language: English
• Published: Department of Earth Sciences, Faculty of Science, Chiba University/Department of Crustal Studies, National Institute of Polar Research/Department of Earth Sciences, Faculty of Science, Chiba University/Department of Crustal Studies, National Institute of Polar Research/Department of Geology, Faculty of Science, Niigata University/Department of Earth System Science, Faculty of Science, Fukuoka University/Department of Crustal Studies, National Institute of Polar Research/Council for Geoscience/Department of Geology, Rand Afrikaans University 2001
• Subjects: Namaqualand; granulite facies; cordierite-phlogopite gneiss; sillimanite pseudomorph after andalusite; spinel-cordierite corona; partial melting; Memoirs of National Institute of Polar Research; Polar Research
• Online Access: https://nipr.repo.nii.ac.jp/?action=repository_uri&item_id=2415; http://id.nii.ac.jp/1291/00002415/; https://nipr.repo.nii.ac.jp/?action=repository_action_common_download&item_id=2415&item_no=1&attribute_id=18&file_no=1

Cordierite-phlogopite gneiss with spectacular coarse pseudomorphs of sillimanite after andalusite occurs as a kind of Mg-Al-rich rock in the Dabeeb-Hytkoras area of the granulite-faces western Namaqualand Metamorphic Complex. The sillimanite pseudomorphs are always fringed by spinel-cordierite coronas, which, in turn, are surrounded by cordierite mono-mineral zones. The spinel-cordierite coronas include minor amounts of sapphirine, corundum and rutile. The matrix comprises mainly cordierite and phlogopite with minor plagioclase and orthopyroxene plus a trace of quartz. Orthopyroxene is often replaced partially by symplectitic intergrowths of phlogopite and quartz. The modes of occurrence and chemical compositions of minerals indicate that the rock followed a prograde metamorphic P-T path from the andalusite to the sillimanite stability fields and a subsequent isobaric cooling path and that partial melting took place during granulite-facies metamorphism resulting in its present geochemical character.