Sector-zoned aegirine from the Ilimaussaq alkaline intrusion, South Greenland: implications for trace-element behavior in pyroxene

Sector-zoned aegirine crystals from a peralkaline nepheline syenite in Ilimaussaq, South Greenland, have been analyzed for major and trace elements using combined electron microprobe and secondary-ion mass spectrometry techniques. Unlike in calcic clinopyroxene, the faster growing basal sector of the sodic clinopyroxene is enriched in incompatible elements relative to the slower growing prism sectors. The prism sectors are enriched in Al and Ti relative to the basal sector. The contrasts between aegirine and augite demonstrate that site characteristics and the ability of a site to accommodate a cation are important factors for controlling sector enrichments. -from Authors