Geochemistry, age and origin of metagreywackes from the Palaeoproterozoic Karrat Group, Rinkian Belt, West Greenland

Abstract

In the Rinkian mobile belt of West Greenland, reworked Archaean gneisses are overlain by a supracrustal sequence, the Karrat Group, dominated by a monotonous turbidite flysch formation consisting almost entirely of alternating metagreywackes and pelitic schist layers. The flysch formation is up to 5 km thick and is the most prominent unit in an area 400 km from north to south that is bounded by Greenland's Inland Ice to the east and Baffin Bay to the west. A similar supracrustal unit underlies extensive areas in the Foxe fold belt of north-eastern Canada. SHRIMP U–Pb study of detrital zircons was carried out on two metagreywackes. In one sample most zircons are 2000–2100 Ma old, with a minor proportion of Archaean zircons; another sample yielded very few zircons, all of Archaean age. Deposition of the Karrat Group took place ∼2000 Ma ago or slightly later. Chemical data combined with Rb–Sr and Sm–Nd isotope information indicates that a large proportion of the sediment was derived from a Palaeoproterozoic arc, with the remainder formed by erosion of the Archaean basement. The Karrat Group is thus among the largest depositories of juvenile Palaeoproterozoic crustal material recognised in West Greenland. The location of the arc that provided most of the detritus to form the Karrat metagreywackes is not known.