Provisional results of isotope investigations into quartzo-feldspathic rocks from Kangiussap nunâ, Ivisârtoq sheet, southern West Greenland

The geology of Kangiussap nuna has been described by Walton (1976), Allaart et al., (1977) and more recently, folIowing 1:20000 mapping, by Coe & Robertson (1982) (see also Brewer et al., this report). A heterogeneous banded gneiss believed to be Amitsoq is intruded by multiphase Nl1k gneiss. Coe & Robertson (1982) recognised five phases of Nl1k gneiss (Nl1k 1-5). These are cut by undeformed to weakly foliated granites and pegmatites which were judged to be of Qorqut age (Coe & Robertson, 1982). This report presents the results of Rb-Sr whole rock-analyses and provisional Pb isotope results on representative samples of Nl1k 1 to 4 and Qorqut granite (terminology of Coe & Robertson, 1982). These samples were collected during field mapping in 1981 as part of the Ivisiirtoq project for the Geological Survey of Greenland at the University of Exeter. Rb-Sr ratios were determined by X-ray fluorescence spectrometry at the University of Oxford. Sr and Pb isotopes were measured in the same laboratories on VG Micromass 30 and Isomass 54E mass spectrometers, respectively. The generous assistance of P. N. Taylor and S. Moorbath is gratefully acknowledged.