Metamorphic Evolution of the Koettlitz Group in the Koettlitz-Ferrar Glaciers Region (Southern Victoria Land, Antarctica)
F.M. Talarico1*, R.H. Findlay2 & N. Rastelli3
1Dipartimento di Scienze della Terra, Università di Siena - Italy
2Department of Mining and Petroleum, Geological Survey Division, Port Moresby - Papua New Guinea
3Museo Nazionale dell’Antartide, Sezione Scienze della Terra, Università di Siena – Italy
Received 24 June 2003; accepted in revised form 13 April 2005
Abstract - 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<Ptot = 5.6-7.8 kbar, T = 670-713 °C. The subsequent syn-D2 retrograde P-T path confirms significant decompression accompanied by moderate cooling and indicates an incomplete re-equilibration of early medium-P assemblages at lower P-T conditions (1.7-5.3 kbar, 534-644 °C).
Petrological data from the Koettliz Group, allied to available radiometric dating, support in southern Victoria Land a thermotectonic model involving crustal thickening at > 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.
*Corresponding author (talarico@unisi.it)