Rb-Sr and U-Pb age patterns in polymetamorphic sediments from the southern part of the East Greenland Caledonides

Rb-Sr analyses on sediments once believed to be late Precambrian show evidence of a middle Proterozoic metamorphic event overprinted by a Caledonian event which only partly reset the isotopic systems. U-Pb analyses on monazites support the Rb-Sr data, whereas zircons show evidence of a detrital origin from an older source region. The age patterns support speculation of the presence of widespread early Proterozoic deposition and a signifiiant middle Proterozoic orogenic episode within the East Greenland Caledonides.