The Kuunga Accretionary Complex Of Sverdrupfjella, Western Dronning Maud Land, Antarctica.

Abstract

Three complexes are recognised in Sverdrupfjella WDML, Antarctica. A western basal ~1140Ma Jutulrora Complex, consisting mostly of arc-related TTG orthogneiss with evolved Sr-Nd isotopic signatures with TDm ages >2by; structurally overlain by the Fuglefjellet Complex, comprising supracrustal intercalated ~800-900Ma carbonates and ~1100-1200Ma quartzo-feldspathic gneisses; in turn in the east overlain by the Rootshorga Complex which contains paragneisses with minor orthogneisses (~1100-1200Ma), intruded by granitic orthogneiss of similar age. Sr-Nd isotopic signatures from the Fuglefjellet and Rootshorga Complexes have TDm ages <1.8by. D1 and D2 deformation verges top-to-NW. In contrast D3 deformation verges top-to-the-SE. In the Jutulrora Complex, D3 comprises ~100m 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. Zircon ages of the granitic sheets are 490-500Ma. Sr-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. P-T-t studies from the Rootshorga Complex yield an ITD path with decompression from ~1.4Gpa at ~570Ma to ~0.7Gpa at ~500Ma whereas P-T-t estimates from the Jutulrora Complex are <~0.8Gpa at ~500Ma with a path consistent with crustal loading. The Rootshorga and Fuglefjellet Complex are inferred to comprise a mega-nappe, emplaced during the Kuunga Orogeny ~500Ma ago, over the footwall Jutulrora Complex. Geophysical data are consistent with this interpretation.