DISCOVERY OF THE GUBBEDALEN SHEAR ZONE (GSZ): AN IMPORTANT TERRANE BOUNDARY WITHIN THE EAST GREENLAND CALEDONIDES OF LIVERPOOL LAND

Rocks and structures in Liverpool Land, Northeast Greenland present an interesting problem due to the appearance of 395 Ma eclogites proximal to 425 Ma undeformed granites. Our work has revealed a 300-400 m thick, N-dipping high strain zone, that we named the Gubbedalen shear zone (GSZ). The hanging wall to the north is an upper amphibolite-facies paragneiss complex with distinctive marbles (i.e. Krummedal Sequence) that is intruded by nonmetamorphosed 425 Ma Caledonian granites (i.e. Hurry Inlet Granite). This hanging wall block is intruded by N-S striking lamprophyre dikes that are absent in the footwall. The footwall block is a basement complex comprising mainly orthogneiss, migmatite, and boudinaged mafic bodies with minor variably retrograded eclogites, garnet-proxenites, amphibolites, and ultramafic bodies. The footwall block is injected by a plethora of post-metamorphic felsic dikes. We report a 380 Ma U-Pb date on zircons from one of the dikes cutting the amphibolite facies structures and fabrics. Mylonitization has overprinted the felsic dikes and progressively increases in intensity structurally upwards into the GSZ. The structurally lower section of the GSZ has crystal-plastic retro-mylonites with kinematic indicators documenting tops-to-the South thrusting, consistent with the orientations of boudinaged mafic bodies in the footwall. The uppermost section of the GSZ is characterized by a tops-to-the North extensional brittle fault. The GSZ, therefore, juxtaposes terranes with distinctly different protolith settings and tectonometamorphic histories. Since Permian reconstructions of the Caledonides show Liverpool Land occupying an internal position within the orogen, we explore the implications of the Gubbedalen shear zone as an important terrane boundary within this tectonic setting.