The Kuunga Accretionary Complex of Sverdrupfjella and Gjelsvikfjella, western Dronning Maud Land, Antarctica

The ~ 550 Ma Kuunga Orogeny extends from the Damara in Namibia, through the Zambesi and Lurio orogenic belts in Zambia and Mozambique, southern Africa, through Dronning Maud Land and Princess Elizabeth Land, Antarctica into western Australia. Sverdrupfjella is located at the western end of Dronning Maud Land where the Kuunga Orogeny is inferred to post–date and overprint the East African Orogeny. Three complexes are recognized in Sverdrupfjella western Dronning Maud Land, Antarctica. A western basal ~ 1140 Ma Jutulrora Complex, consisting mostly of arc–related tonalitic trondjhemitic orthogneiss with evolved Sr–Nd isotopic signatures with T_Dm ages >2 Ga. It is structurally overlain by the Fuglefjellet Complex, comprising supracrustal ~ 800–900 Ma carbonates intercalated with quartzo–feldspathic gneisses with detrital zircons of ~ 1000–1200 Ma age with ~ 500 Ma overgrowths. The Fuglefjellet Complex is overlain in the east by the Rootshorga Complex containing paragneisses with minor orthogneisses (~ 1100–1200 Ma), intruded by granitic orthogneiss of similar age. Strontium–Nd isotopic signatures from the Rootshorga Complex has T_Dm ages <1.8 Ga. D₁ and D₂ planar fabrics typically dip to SE with vergence top–to–NW in all complexes. D₃ deformation verges top–to–the–SE. In the Jutulrora Complex, D₃ comprises ~ 100 m scale folds with NW dipping axial planes, cut by SE dipping dilational granite sheets. In the Rootshorga Complex D₃ is characterised by syntectonic granite veins with extensional and compressional displacements with top–to–the SE shear. Discordancies are consistent with low angle thrust planes at Fuglefjellet and Kvikjolen with probable repetition of carbonate layers. Zircon ages of the granitic sheets are 490–500 Ma. Strontium and Nd isotopic signatures of the granitic sheets intruded into all complexes are consistent with melting of Jutulrora Complex crust with Archaean and Mesoproterozoic xenocrysts in some samples. Top–to–SE shear zones displace pegmatites with an inferred age of 520 Ma and are syntectonic with layer parallel ~ 490 Ma granite sheets. P–T–t studies from the Rootshorga Complex yield isothermal decompression paths at ~ 800–900 °C with decompression from ~ 1.4 GPa at ~ 570 Ma to ~ 700 °C and ~ 0.7 GPa at ~ 500 Ma whereas P–T–t estimates from the Jutulrora Complex are ~ 600–700 °C and < ~ 0.8 GPa at ~ 500 Ma with a path consistent with crustal loading. The Rootshorga and Fuglefjellet Complex are inferred to comprise a mega–nappe, emplaced during the Kuunga Orogeny ~ 500 Ma ago, over the footwall Jutulrora Complex. Aerogravity, satellite gravity and seismic tomography data reflecting unusually thick crust are consistent with this interpretation.