U-Pb geochronology of Neoproterozoic and Caledonian tectonothermal events in the East Greenland Caledonides

The East Greenland Caledonides occupy a crucial position in plate-lec tonic reconstructions of the Late Mesoproterozoic to Early Neoproterozoic Grenville-Sveconorwegian belt. We present new field and isotopic data from the northern Stauning Alper which indicate that the 1050-930 Ma history of the area was characterized by deposition of extensive elastic sequences. Sources of detritus were dominated by rocks of Mesoproterozoic age, with only limited contributions from Archaean sources, suggesting deposition at a distance from the present Caledonian foreland. A Neoproterozoic granite (938 +/- 13 Ma) provides evidence for thermal perturbation at a time of extensional collapse and uplift recorded in NW Scotland, the Grenville Bell of Canada, Labrador and the Sveconorwegian of SW Sweden and southern Norway. Widespread anatexis in the northern Stauning Alper at c. 430-425 Ma resulted from both collisional melting and decompression melting on uplift contemporaneous with the early part of orogenic collapse of the Caledonian Fold Belt. Caledonian deformation was Focused at the zone of most extensive granite emplacement. Isotopic evidence suggests that Caledonian granites, previously thought to be entirely post-kinematic, actually predate late Caledonian extension.