The Pressure Character of the Low-Grade Metapelites from Robertson Bay Terrane, northern Victoria Land (Antarctica).

The geobarometric method based on the b spacing of the white K-micas in metapelites was utilized to determine the pressure character of the metamorphism in Robertson Bay Terrane (RBT) and Bowers Terrane (BT). Analytical results indicate that no significant differente exists between RBT and BT, and that all b data (240) are close to an average value of 9.027 (3) A. The conclusion is that both RBT and BT metamorphisms fall in the range of intermediate-pressure (i.e. Barrovian-type) metamorphisms, and can be related to a thermal metamorphic gradient not higher than approximately 15°C/km. Consequently, plate-tectonic models for northern Victoria Land should take into consideration, as further constraints, the identical metamorphic features of the RRT and BT, and the prevalence of relatively low thermal gradients during the metamorphic climax. This constraint suggests at, in the early Paleozoic, the RBT and the BT both belonged to the same, relatively deep, crustal level, and were both metamorphosed at a considerable depth underneath a thick tectonic cover.