Origins of compositional heterogeneity in olivine-hosted melt inclusions from the Baffin Island picrites

The Baffin Island picrites are highly magnesian (< 22 wt% MgO) olivine tholeiites, erupted through felsic continental crust. Plots of most major and minor element oxides against MgO for the lavas define very tight trends consistent with modification of melts parental to the erupted suite by olivine fractionation or accumulation. However, melt inclusions trapped in primitive olivine phenocrysts in these lavas have much more diverse compositions. After correction for post-entrapment modification, the inclusions are systematically slightly lower in Al2 O3, and significantly higher in SiO2, K2O and P2O5 than the lavas' fractionation trends. CaO, Na2O and TiO2 contents lie within the lavas' fractionation trends. Similarly, most inclusions are higher in Sr/Nd, K/Nb, Rb/Ba, Rb/Sr, U/Nb and Ba/Th than the lavas. These characteristics resulted from up to ≈15% contamination of evolving picritic-basaltic liquids by locally-derived, broadly granitic partial melts of the quartz + feldspar-rich crust through which the picrites erupted. Contamination was minor in the bulk lavas (