Rare earth geochemistry of basalts from Norfolk Island, and implications for mantle inhomogeneity in the rare earth elements

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 in homogeneously distributed in the source region for the basalts. © 1978, GEOCHEMICAL SOCIETY OF JAPAN. All rights reserved.