Early Neoproterozoic events in East Greenland

Abstract

East Greenland forms one of the least understood of the orogenic belts formed during the amalgamation of Rodinia during late Mesoproterozoic times. Recent U–Pb zircon SHRIMP dating on the widespread Krummedal supracrustal succession and associated granites from central East Greenland has shown that metamorphism and intrusion affected the region at around 0.95–0.92 Ga, approximately 150 m.y. later than the main phase of Grenvillian orogenesis ( s. s.). These early Neoproterozoic ages may indicate a link with metamorphism and igneous activity in the Sveconorwegian Belt of Scandinavia rather than true ‘Grenvillian’ events on the eastern margin of Laurentia. Previous plate tectonic reconstructions which link Laurentia and Baltica by a collisional margin extending through central East Greenland at 1.1 Ga were based on early conventional U–Pb zircon dating in central East Greenland, and can no longer be considered viable. Instead, new detrital zircon SHRIMP U–Pb dating studies show that the Krummedal supracrustal succession was deposited between ca. 1.0 Ga and no later than 0.95 Ga, during a time of major sediment deposition widely preserved elsewhere in the North Atlantic region. Erosion associated with post-1.1 Ga collapse of the Grenville–Sunsas orogeny is the most likely source for the majority of the detritus, since the corresponding Baltic margin was dominated by A-type magmatism for much of the period 1.4–1.1 Ga material, which is the age of the bulk of detrital zircons in the Krummedal supracrustal succession. We suggest that the Krummedal supracrustal succession was deposited east or south-east of its present location, and was thrust onto Archaean–Palaeoproterozoic orthogneisses, which in turn were displaced across the parautochthonous foreland during the Caledonian orogeny. The early Neoproterozoic orogenic events recorded in central East Greenland therefore involved the metamorphism of a metasedimentary package of Laurentian–Amazonian affinity during the Sveconorwegian orogeny in the final stages of the collision of Baltica and Laurentia.