Malene stratigraphy and late Archaean structure: new data from Ivisârtoq, inner Godthåbsfjord, southern West Greenland

Abstract

This report summarises the principal results of a six-week study of some critical areas in Ivisârtoq (part of the Ivisârtoq region, 65 V. 2 Nord; fig. 1) by a two-man expedition (the writer and his undergraduate assistant) during the summer of 1985, a period of exceptionally good weather. Our objective was to complete the field programme of a team from the University of Exeter (Chadwick et al., 1983; Brewer et al., 1984) which had been seriously disrupted by bad weather in 1983. The main thrust of the field work in 1985 was to investigate the geometry of the late Archaean system of dornes of gneisses and intervening synclinal cusps of Malene supracrustal rocks which dominates the structure of Ivisârtoq (figs 1,2). The fjeld mapping revealed important new details, not only of the structure but also of the Malene stratigraphy and the emplacement of granitic and basaltic magmas during the development of the system of dornes and synclines. Systematic geological investigations in the Ivisårtoq region began in 1976 (Allaart et al., 1977) and important contributions have been made by Hall & Friend (1979, 1983), Hall (1980, 1981) and Friend et al. (1981). Some preliminary results of investigations by the Exeter team have been reported by Brewer et al. (1984), Chadwick (1985), and Coe & Robertson (1984). Details of isotopic ages and petrogenesis of the gneisses and late Arehaean granites have been reported by Robertson (1985, in press).