Mid-Archaean basic magmatism of southern West Greenland

dykes within the Am~tsoq gneisses and a series of large metagabbr~anorthosite complexes. The Malene rocks range from komatiitic to tholeiitic in chemical affinities and occur as extensive intermixed horizons throughout the craton. Metavolcanic amphibolites which are intercalated with the older Am]tsoq gneisses are chemically similar to those which are isolated from them. They probably all represent lavas erupted in an oceanic environment, some of which were subsequently tectonically intercalated with the older sialic crust. Significant geochemical differences between the Malene metavolcanic rocks and the Ameralik basic dykes, which intrude the Am~tsoq gneisses, suggest that these dykes could not have acted as feeders to he Malene lavas. The petrogenesis of the Malene rocks is considered in terms of normative behaviour and of the system CaO-MgO-AI203-SiO 2 (CMAS). Both demonstrate the importance ofolivine and clinopyroxene in the evolution of the Malene magmas nd suggest that they were derived from relatively garnet-depleted and clinopyroxene-enriched mantle compared to average modern mantle. Evidence for a complementary aluminous portion f the Archaean mantle is provided by the abundance of metagabbro-anorthosite rocks and associated aluminous tholeiitic metavolcanic amphibol-ites. The lithostratigraphy of the Archaean craton of southern West Greenland has been determined from field relationships which have been de-scribed by several authors (eg McGregor 1973