Emplacement of rapakivi granite and syenite by floor depression and roof uplift in the Palaeoproterozoic Ketilidian orogen, South Greenland

Abstract

In the Palaeoproterozoic Ketilidian orogen of South Greenland, tabular intrusions of the rapakivi granite suite exposed at Graah Fjelde, Lindenow Fjord and Qernertoq, and a Mesoproterozoic syenite of the Gardar province exposed at Paatusoq, were emplaced by a combination of roof uplift and floor depression. The strain associated with the emplacement of the intrusions mainly involved redistribution of mass vertically within the lithosphere. Space for the emplacement of the rapakivi plutons was not created during regional extension on low-angle, ductile shear zones as claimed by some previous workers and there is no evidence that emplacement of the intrusions coincided with extensional collapse of the orogen following crustal thickening. The rapakivi granites post-date peak metamorphism in the orogen by 35–46 Ma and their contacts cross-cut and clearly post-date intense, flat-lying D1/D2 fabrics that formed by partitioning of deformation into arc-normal and arc-parallel components during oblique convergence.