High-TiO2 Basalts at Iceland and the North Atlantic Igneous Province

Although basalt genesis in the North Atlantic Igneous Province has usually focused on the origin of primitive, often picritic, lava and intrusions with high crystallization temperatures and relatively depleted compositions, most basalts dating from the Paleocene are those aptly characterized as having higher parental TiO2, greater average differentiation, lower crystallization and potential temperatures, and geochemical enrichment. They occur together with low-TiO2 basalt at West and East Greenland, Iceland and Scotland. They are abundant at central volcanoes, where strongly differentiated felsic andesites, icelandites and rhyolites are also common, whereas the low-TiO2 basalts are mostly found along adjacent coeval rift systems. They are absent along spreading ridges at depths >2000 m, and indeed along the approaches to Iceland along Reykjanes and Kolbeinsey Ridges. They do not conform to the global array of spreading-ridge basalts, which have systematically lower parental Na8 and Ti8, are more severely depleted, do not erupt from central volcanoes, and which have far fewer, usually no, affiliated felsic lavas. Low-TiO2 basalts, on the other hand, resemble least titanian abyssal tholeiites. The classic hallmark of documented basaltic differentiation, Skaergaard intrusion in East Greenland, had enriched, high-TiO2 parentage. At Greenland and Scotland, both low- and high-TiO2 basalts erupted along rift systems in ancient continental crust beneath which sub-continental lithospheric mantle is present. Melting was influenced by the presence of refractory (harzburgitic) mantle, which may have cast its signature on the low-TiO2 basalts, and lower continental crust, from which some attributes of the high-TiO2 basalts and many of the felsic lavas and tuffs originated. On this basis, sources of low-TiO2 basalt along Reykjanes and Kolbeinsey Ridges could include delaminated or laterally injected sub-continental mantle, but no continental crust, whereas Iceland itself is partly underlain by continental crust (1). (1) Foulger, G.R., et al., 2019, this session. The Greenland-Iceland-Faroe Ridge is continental.