LOW-PRESSURE GRANULITE-FACIES METAMORPHISM IN THE PRYDZ BAY REGION, EAST ANTARCTICA

• Main Authors: モトヨシ ヨウイチ, Yoichi MOTOYOSHI, D.E. THOST, B.J. HENSEN
• Format: Report
• Language: English
• Published: ABSTRACT 1990
• Subjects: East Antarctica; Prydz Bay; Sheraton; Collerson; Antarc*; Antarctica
• Online Access: https://nipr.repo.nii.ac.jp/?action=repository_uri&item_id=2644; http://id.nii.ac.jp/1291/00002644/; https://nipr.repo.nii.ac.jp/?action=repository_action_common_download&item_id=2644&item_no=1&attribute_id=18&file_no=1

The terrain along the coastal line of Prydz Bay is underlain by granulite-facies rocks of various kinds including pelitic to psammitic gneisses, basic to intermediate gneisses and subordinate amounts of calc-silicate rocks and ultramafic rocks. Extensive partial melting has been observed in pelitic to psammitic gneisses. The age of metamorphism has been dated to be Late Proterozoic based on a Rb-Sr whole rock isochron (SHERATON and COLLERSON; BMR J. Aust. Geol. Geophys., 8,119,1983). The rocks have been subjected to low-pressure granulite-facies metamorphism as evidenced by the following petrographical observations. 1) Pelitic to psammitic gneisses : Cordierite occurs regionally in pelitic gneisses. Andalusite and sillimanite coexist in a cordierite gneiss, in which andalusite occurs as a retrograde mineral being associated with chlorite. 2) Basic to intermediate gneisses : Orthopyroxene occurs regionally in basic to intermediate gneisses, being occasionally associated with clinopyroxene, amphibole and biotite. Garnet is rare, but where it occurs, coronas composed of plagioclase+clinopyroxene+magnetite symplectite are observed around garnet. 3) Ultramafic rocks : Olivene+plagioclase intergrowth is observed in ultramafic rocks. Mineral equilibria and geothermo-barometries yield initial P-T conditions around 750℃ at 5±1 kbar. Prior to the low-pressure granulite-facies metamorphism (possibly in Late Proterozoic), the rocks had been recrystallized at much higher P-T conditions around 950-1050℃ at≃10kbar deduced from local occurrence of pyrope-rich garnet (up to X_<Mg> 70-72) in basic granulites.