Rare earth element abundances in rocks and minerals from the Fiskenaesset Complex,West Greenland

Rare earth element (REE) abundances determined by activation analysis in rocks, plagioclase and mafic separates from the Fiskenaesset Complex are presented together with data on major and trace elements in the minerals. The REE data for the rocks and plagioclases are distinct from those of many other anorthositic complexes and the abundances are some of the lowest recorded for plagioclase from terrestrial anorthosites. The bulk and trace element compositions of the Fiskenaesset plagioclases show a number of similarities to those of lunar plagioclases. The plagioclases show a positive Eu anomaly of about 10 and a depletion in the heavy REE relative to the light ones. The mafic separates are enriched in the heavy REE relative to the light ones, and show no Eu anomaly except in one sample with a positive anomaly not attributable to plagioclase contamination. It is estimated, from experimental partition coefficient data, that the REE pattern in the magma at an early stage of fractionation was La (17×) to Lu (0.7× chondrites) with a possible positive Eu anomaly. This highly fractionated REE pattern may be attributed to partial melting of a garnet-bearing source.