Two tectonically significant enclaves in the Nordre Strømfjord shear zone at Ataneq, central West Greenland

The Nordre Strømfjord shear zone is a 1.8 Ga zone of largescale, transcurrent and sinistral ductile shear (Sørensen et al. 2006) within the Nagssugtoqidian Mobile Belt (NMB) of central West Greenland. It has been hypothesised that the NMB is a suture between two Archaean continental masses (Kalsbeek et al. 1987). During field work in 2005 along the Nordre Strømfjord shear zone in the fjord Ataneq (Fig. 1), some unusual rock types were discovered that preserve evidence of magmatic and metamorphic processes not previously reported in the area. These observations include the first indication of high-pressure (HP) metamorphism in West Greenland and the first reported occurrence of a cumulate of giant orthopyroxene. The tectonic telescoping of these features together within the Nordre Strømfjord shear zone has important implications for reconstructing the Palaeoproterozoic history of this region, and provides evidence that processes typical of Phanerozoic continent–continent collision zones (e.g. the Caledonian and Alpine systems) operated at least as far back as 1.8 Ga ago.