Significance of rare earth distributions in coexisting minerals of peralkaline undersaturated rocks

Rare earth element (REE) abundances in eudialytes and co-existing feldspars and mafic minerals from six alkaline intrusions ranging from mildly to strongly peralkaline indicate large scale complexing of the REE and yttrium. The eudialyte-bearing stages of these intrusions are characterized by a low Ce/Y ratio. This enrichment in the heavy REE is not due to the high REE content of the mineral eudialyte but appears to be related to the importance, duration and type of REE and other element complexing during differentiation. Feldspar and mafic mineral REE abundances reflect this low Ce/Y ratio and are often altered by late stage magmatic, metasomatic or hydrothermal fluids enriched in the heaviest REE and yttrium.