Major Element Records of Variable Plume Involvement in the North Atlantic Province Tertiary Flood Basalts

Major element variations in North Atlantic Tertiary Province primitive, early erupted, alkaline-transitional-tholeiite basalts, recalculated to a restricted value of MgO, give insights into the process of plume-related magmatism. Basalts primitive enough to be crystallizing only olivine were recalculated to a proposed primary magma composition of 15 wt % MgO. The recalculated dataset shows clear inter-element correlations including a strong, significant, negative correlation between Fe and Si indicating polybaric melt segregation. Overlap between basalt compositions and experimental melts from a fertile, Fe-rich, low mg-number (85.5) peridotite suggests that, relative to normal peridotite with mg-number > 89, the North Atlantic basalt source was Fe rich. Linear regression of the experimental data gives apparent pressures of magma segregation of 17·5–37 kbar, with intra-region variability in the depth derivation from the melt column for each sample, thus suggesting that lithospheric thickness ‘lid-effect’ control on magma generation may have been overemphasized in recent studies. Comparable source composition, magma segregation depth and calculated mantle potential temperature (1440–1460°C) throughout the Province supports the previously suggested plume impact model, arriving below East Greenland, derived from a variably enriched and depleted lower-mantle source. Given the good agreement between conclusions drawn from major element data and previously published results we suggest that restricted-MgO recalculated datasets may be usefully applied to study other large igneous provinces.