The Archaean Skjoldungen alkaline province, South-East Greenland

Abstract

An alkaline province has been found to constitute a significant part of the Archaean terraines in the Skjoldungen area, 63°N in South-East Greenland. A total of twenty-four alkaline complexes and syenite gneiss areas has been identified. The alkaline magmatism is regarded as syn- to post-tectonic to judge from the wide variation in the degree of deformation. A large number of intrusions are virtually undeformed. Petrographically the province encompasses slightly SiO₂-undersaturated mafic to SiO₂-saturated syenitic rocks and a carbonatite-bearing nephelinitic complex. Neodymium-samarium model ages and a zircon age show the alkaline rocks to be c. 2800 Ma old and the province thus constitutes the largest group of Archaean alkaline rocks yet found on Earth. The chemical characteristics, including very low concentrations of most trace elements except Ba and Sr, recall those of the younger alkaline Seiland province in Norway and the Haliburton-Bancroft province in Canada.