Metamorphic evolution of the Koettlitz Group in the Koettlitz-Ferrar Glaciers region (southern Victoria Land, Antarctica)

Polyphase medium- to high-grade metamorphism is described in the Koettlitz Group in the region between the Koettlitz and Ferrar Glaciers (southern Victoria Land, Antarctica). The critical metamorphic mineral assemblages define five metamorphic zones: muscovite+sillimanite and K-feldspar+sillimanite (in metapelites), biotite+calcite, Ca-amphibole, and Ca-pyroxene (in calc-silicate rocks). This metamorphic zonation, with increasing grade from the southwest to the northeast, developed during a syn-D1 progressive intermediate-P metamorphism with metamorphic peak conditions of PH2O 540 Ma, followed by magmatic accretion and low P / high T metamorphism at c. 500 Ma. All events occurred within the broadly convergent Neoproterozoic/Early Palaeozoic regime of the Ross orogenic belt in the Ross Sea sector of the palaeo-Pacific margin of Gondwana.