Controls of Mantle Potential Temperature and Lithospheric Thickness on Magmatism in the North Atlantic Igneous Province

Modelled primary magma compositions of Palaeogene basalts from the North Atlantic Igneous Province (NAIP) require melting at mantle potential temperatures (T-P) in the range 1480-1550A degrees C. Modern lavas from Icelandic rift zones require T-P similar to 1500A degrees C and those from the rift flanks T-P similar to 1450A degrees C. Secular cooling of the NAIP thermal anomaly was therefore of the order of similar to 50A degrees C over the past 61 Myr. There were systematic variations in T-P of 50-100A degrees C from the centre of the thermal anomaly to its margins at any one time, although limits on the stratigraphical distribution of T-P determinations do not rule out thermal pulsing on a timescale of millions of years. Variation in extent of melting at similar T-P was controlled by local variability in lithospheric thickness. In the west of the NAIP, lithosphere thickness varied from similar to 90 km at Disko Island to similar to 65 km at Baffin Island, with similar thickness variations being evident for magmatism in the Faroe Islands, Faroe-Shetland Basin and the British Palaeogene Igneous Province (BPIP). Mean pressure of melting was greater than or equal to the final pressure of melting; the two values converge for melting columns with a melting interval of < 1 center dot 5 GPa, regardless of T-P. The majority of the BPIP magmas were generated in the garnet-spinel transition in the upper mantle. Calculated and observed rare earth element distributions in NAIP lavas are entirely consistent with the melting regimes derived from major element melting models. This allows a calibration of rare earth element fractionation and melting conditions that can be applied to other flood basalt provinces.