GEOCHRONOLOGY OF ARCHEAN AND PROTEROZOIC EVENTS IN THE AMMASSALIK AREA, SOUTH-EAST GREENLAND, AND COMPARISONS WITH THE LEWISIAN OF SCOTLANDAND THE NAGSSUGTOQIDIAN OF WEST GREENLAND

The Ammassalik area in South-East Greenland forms a link between the P recambrian terrains of West Greenland and northwest Scotland. It consi sts mainly of Archaean orthogneisses reworked during a Proterozoic tec tonothermal event. Proterozoic ortho- and paragneisses, major leuconor ite-charnockite complexes, suites of metadolerite dykes and posttecton ic granites also occur. Sm-Nd, Rb-Sr, Pb-Pb and zircon U-Pb isotope da ta yield ages of approximately 3.0-2.8 Ga for Archaean basement gneiss es, 2.2-2.1 (?) Ga for Proterozoic gneisses, 1.9-1.8 Ga for the Proter ozoic reworking, 1.89 Ga for the leuconorite-charnockite complexes, an d 1.7-1.6 Ga for the late granites. Proterozoic reworking has disturbe d most Archaean isotope systems, and contamination with Archaean mater ial makes dating of Proterozoic rocks difficult. In several cases disc ordant dates are obtained from different isotope systems. The chronolo gies of the Lewisian complex of Scotland and the West Greenland Nagssu gtoqidian mobile belt compare closely with that of the Ammassalik area , and support the correlation between these areas suggested by earlier studies. There are, however, also major differences between the Nagss ugtoqidian and the mobile belt in the Ammassalik area, and precise cor relation across the Inland Ice of Greenland is still ambiguous.