Rb-Sr whole rock isochron ages of 1950 m.y. and 1725 m.y. obtained on rock units of the Hagar migmatite sheet indicate that it is an early Proterozoic gneiss complex and not part of a mobile Caledonian infrastructure. New isotopic ages and recent fieldwork give no support to the concept of mobile Caledonian migmatitic masses rising into the suprastructure as envisaged in the classic "stockwerke" model for the East Greenland Caledonian fold belt. However, K-Ar mineral ages ranging from 415-462 m.y. indicate a significant Caledonian thermal event. Relationships between the Hagar sheet and bordering metasediments are discussed, including evidence for a middle Proterozoic group of sediments metamorphosed before deposition of the late Precambrian Petermann Series and Eleonore Bay Group.
have established the presence of important Archaean and early Proterozoic elements within the metamorphic complexes of the southernmost part of the fold belt (Steiger and Henriksen, 1972; Hansen etal., 1973a Hansen etal., , 1974;;Rex and Gledhill, 1974;Hansen, 1976), and led to substantial revision of the development of the Caledonian orogeny in East Greenland (Henriksen and Higgins, 1976; Higgins, 1976). However, it is only in the last few years that studies have been extended to the classic area of the fold belt between 72-74 ~ N (Friderichsen and Higgins, 1976;Rex et al., 1976Rex et al., , 1977;;Higgins et al., 1977), including the section between the Petermann Series and the Hagar migmatite sheet in the Kn~ekdal region at the western end of Kejser Franz Josephs Fjord (Figs. 1 and4).