Multiple thermal events recorded in metamorphosed carbonate and associated rocks from the southern Austkampane region in the Sør Rondane Mountains, East Antarctica: A protracted Neoproterozoic history at the Gondwana suture zone

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This paper provides a detailed analysis of the geological evolution of the southern Austkampane region in the Sør Rondane Mountains, Antarctica, using geological and petrographical observations, geochemical, geochronological, radiogenic, and stable isotopic data, and metamorphic petrological techniques. The study area is dominated by felsic gneisses intercalated with mafic and carbonate rocks. Carbonate rocks include several calc-silicate and mafic to ultramafic blocks with carbonatite-like characteristics. The new data presented here indicate the presence of five important thermal events in the geological history of the region, at c. 1060, 770–750, 655–635, 560–545, and <545Ma. The c. 1060Ma event is characterized by granitic volcanic arc magmatism, possibly in an active continental margin setting, involving magmas that may have been sourced from enriched mantle formed by subduction of older crustal material during the formation of Rodinia. The oldest T(DM) age for this suite is 3.4Ga. The 770–750Ma event is characterized by both mafic and felsic magmatism in an active continental margin setting, with magmas being similar to bulk earth composition. The 655–635Ma thermal event is represented by granulite-facies metamorphism along an anticlockwise pressure–temperature path, involving heating of the lower crust at a continental margin, and subsequent obduction of a cratonic counterpart during collision. Granitic and basaltic magmatism at 560–545Ma is also associated with retrograde metamorphism and hydration-related partial melting of marble. The carbonate melt, and granitic and basaltic magmas during this event coexisted with each other and formed metasomatic calc-silicates and hornblendites, respectively. The final event at <545Ma is characterized by the intrusion of an undeformed quartz syenite dyke, which may be related to either (1) collision and melting of preexisting lower crustal material, or (2) melting of slightly enriched mantle material in an extensional tectonic setting following the earlier collisional event. The five thermal events between c. 1100 and 500Ma recognized in this study from a narrow region of the Sør Rondane Mountains, suggest that a combination of geochronological, whole-rock, and isotope geochemical analyses of metamorphic rocks and the pressure–temperature evolution could constrain the processes that operated during the amalgamation and break-up of Rodinia and the formation of Gondwana. A similar approach is essential in neighboring Gondwana terranes for modeling the protracted events of Neoproterozoic orogenesis.