Tab. 1+2: Representative electron-microprobe analyses of minerals from Du Toit Nunataks

• Main Authors: Schubert, Wolfgang, Olesch, Martin
• Format: Dataset
• Language: English
• Published: PANGAEA 2011
• Subjects: -; Aluminium; Aluminium (IV); Aluminium (VI); Aluminium oxide; Barium; Barium oxide; Calcium; Calcium oxide; Chromium; Chromium(III) oxide; Comment; Du Toi Nunataks; Read Group; Shackleton Range; Antarctia; Geological sample; GEOS; Hatch_Plain; Iron 2+; Iron 3+; Iron oxide; FeO; Magnesium; Magnesium oxide; Manganese; Manganese oxide; Microprobe; Mineral name; Number of oxygens; Potassium; Potassium oxide; Sample code/label; Silicon; Silicon dioxide; Sodium; Sodium oxide; Sum; Titanium; Titanium dioxide; Antarctic; Du Toit Nunataks; Hatch Plain; Read Mountains; Shackleton; Antarc*; Antarctica; Polarforschung
• Online Access: https://doi.pangaea.de/10.1594/PANGAEA.763845; https://doi.org/10.1594/PANGAEA.763845

An example of cordierite-bearing gneiss that is part of a high-grade gneiss-migmatite sequence is described from the Hatch Plain in the Read Mountains of the Shackleton Range, Antarctica, for the first time. The cordierite-bearing rocks constitute the more melanosomic portions of the metatectic and migmatitic rocks that are associated with relict granulite facies rocks such as enderbitic granulite and enderbitic garnet granulite. The predominant mineral assemblage in the cordierite-bearing rocks is chemically homogeneous cordierite (XMg 0.61) and biotite (XMg 0.47), strongly zoned garnet (XMg 0.18-0.11), sillimanite, K-feldspar (Or81-94Ab5-18An0.6), plagioclase (An28), and quartz. Inclusions of sillimanite and biotite relics in both garnet and cordierite indicate that garnet and cordierite were produced by the coupled, discontinuous reaction biotite + sillimanite + quartz = cordierite + garnet + K-feldspar + H2O. Various garnet-biotite and garnet-cordierite geothermometers and sillimanite-quartz-plagioclase-garnet-cordierite geobarometers yield a continuous clockwise path in the P-T diagram. The P-T conditions for equilibrium between garnet core and cordierite and between garnet core and biotite during peak metamorphism and migmatization were estimated to be 690 °C at 5-6 kb. This was followed by cooling and unloading with continuously changing conditions down to 515 °C at 2-3 kb. This low-pressure re-equilibration correlates with the pressure conditions evaluated by SCHULZE (1989) for the widespread granitic gneisses of the Read Group in the Shackleton Range. The associated relict enderbitic granulites representing low-pressure type granulite (8 kb; 790 °C) are comparable to similar low-pressure granulites from the East Antarctic craton. They were either formed by under-accretion processes after collision (WELLS 1979, p. 217) or they are a product of remetamorphism at P-T conditions intermediate between granulite and amphibolite facies. A model of a multiple imbrication zone with crustal thickening (CUTHBERT et ...