Proterozoic basaltic magmatic periods in North-West Greenland: evidence from K/Ar ages

Abstract

This paper is the third of a series reporting on K/Ar whole rock ages of Proterozoic basaltic rocks of the Thule district, North-West Greenland. The dating programme is a co-operative venture between the Geological Survey of Greenland and The University, Leeds, V.K., and was set up in connection with a 1:500 000 mapping project of the region between 75°N and 78° 45'N (Melville Bugt - Inglefield Land, fig. 1). Field work by one of us (PRD) has shown that several episodes of unmetamorphosed Proterozoic basic igneous rocks can be distinguished stratigraphically in the region (see below). The routine K/Ar isotopic work, carried out concurrently with the field work, has aimed at dating these episodes, thereby providing minimum ages for deposition or consolidation of the host rocks. The two earlier reports (Dawes et al., 1973, 1982a) dealt with sills and dykes from the northern part of the region (Inglefield Land - Prudhoe Land); intrusions that have known or inferred stratigraphic relationships with the Proterozoic Thule Group. The present report gathers together all hitherto unpublished K/Ar dates - 18 in total on both extrusive and intrusive rocks - mainly from the central and southern parts of the region (Inglefield Bredning and Melville Bugt). Six of the samples represent cross-cutting intrusions in the Precambrian Shield that have uncertain age relationships with the overlying Thule Group.