ABSTRACT

The basalts of Norfolk Island range from tholeiites through transitional basalts to alkali olivine basalts, and plot in a unique field on a Ti-Zr-Y diagram. REE abundances in seven representative samples are similar to those in tholeiites and alkali olivine basalts from Hawaii, i.e. light REE enrichment relative to chondrites, and a slightly higher ^La/Yb value for the alkali olivine basalts relative to the tholeiites. Three tholeiitic samples with anomalously high Y (84-105ppm) show unique REE patterns for basaltic rocks, with a relative enrichment of the middle REE. Apart from Y and REE these samples are chemically identical to the ‘normal’ Y-REE tholeiites from Norfolk Island, and it is suggested that the unique Y and REE contents are due to variable Y and REE concentrations in an accessory mantle phase such as apatite and/or the Y acceptor RE phosphate minerals such as xenotime or samarskite inhomogeneously distributed in the source region for the basalts.