Age of rocks, structures, and metamorphism in the Nagssugtoqidian mobile belt, West Greenland - field and Pb-isotope evidence.

Two kinds of structural domains are distinguished in this mobile belt: 'Nagssugtoqidian' shear belts, which wrap around large areas in which 'pre-Nagssugtoqidian' fold structures are preserved. Field and Pb-isotope data are presented which suggest: 1) that some of the gneisses are Archaean, as previously thought, but there are also some gneisses derived from Proterozoic intrusive rocks; 2) most of the supracrustal rocks in the area are probably of Proterozoic age; 3) the main phase of metamorphism took place at 1880 + or - 50 m.y.; and 4) most of the structures developed during a Proterozoic orogeny that can be broadly correlated with the Hudsonian orogeny in the Canadian Shield. Pb-isotope data and Pb/Pb isochron parameters are presented for supracrustal rocks in the Nagssugtoqidian and Rinkian mobile belts of W Greenland, and similar data for the granites and gneisses of W Greenland. -P.Br.