Whole-rock Rb-Sr isochrons have been obtained for three complexes in the Gardar igneous province. For the Kûngnât Fjeld near Ivigtût, an age of 1,245 + 16 m.y., with an initial Sr87/Sr86 ratio of 0.7071 ± 0.0021 has been calculated. The Hviddal composite dike and the intrusively related central complex on Tugtutôq, about 110 km east-southeast of Kûngnât Fjeld, yield ages of 1,187 ± 9 m.y. and 1,180 ± 37 m.y., with initial Sr87/Sr86 ratios of 0.7024 + 0.0010 and 0.698 ± 0.014, respectively. Field relations and other age evidence suggest that the latter intrusions bracket the main magmatism and tectonism in the Tugtutôq region. The new data carry the implication that Gardar magmatism in the Kûngnât Fjeld and Ivigtût districts may be some 50 m.y. earlier than that of the Tugtutôq-Ilímaussaq region.

The Gardar events can be related to events in North America, and evidence is presented in support of the theory that Gardar magmatism represents cratonic activity on the foreland of the Grenville orogenic belt.

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