The tectonothermal evolution of the Kirwanveggen—H.U. Sverdrupfjella areas, Dronning Maud Land, Antarctica

Abstract

Three episodes of deformation spanning a period of ∼900 Ma are recognised. The first deformation at ∼ 1000 Ma involved progressive, yet distinct stages within a protracted, composite event involving recumbent folding, low-angle thrust faulting and locally, highly oblique, transpressive strike-slip shearing. These structures suggest tectonic transport from the south and southeast during D 1. D 2 at ∼500 Ma is variable in the different areas and involved thrust faults and folding with locally developed axial-planar foliations. The orientations of the fault planes and axial-planar structures suggest transport from the west and northwest in western Sverdrupfjella and from the southeast in Kirwanveggen. D 3 involved normal faulting and jointing, adjacent and parallel to the Jutulstraumen Glacier in the west. The joints affect the alkaline complexes, some of which are Jurassic in age and consequently D 3 is related to the breakup of Gondwana. Four phases of metamorphism, related to the deformation, are recognised. The dominant mineral assemblages M 1–3 are typical of medium- to high-grade metamorphism. Discordant mafic intrusions provide evidence of a long history of metamorphism. Mafic nodules from the eastern part of the area contain high-pressure assemblages representing M 1. Assemblages and textures indicate that M 2 was related to isothermal decompression related to the uplift caused by thrust faulting during D 1. The period between M 2 and M 3 appears to have involved annealing at mid-crustal levels. M 3 mineral development is dominated by biotite which is oriented axial-planar to D 2 folds. M 4 assemblages are typically low-grade and involve hydrothermal alteration resulting in chloritisation and sausseritisation related to D 3.