Ti-Rich Tholeiitic Picrites from the Prinsen af Wales Bjerge, East Greenland, and Evidence for a Pyroxene-Rich Mantle Source at Breakup in the North Atlantic.

Highly magnesian, olivine-phyric tholeiitic basaltic and picritic lavas with >5 wt% TiO₂ from the Prinsen af Wales Bjerge (PAWB) region are chemically distinct from all other Paleogene East Greenland flood basalts and from basalts in the North Atlantic Igneous Province. The ~100-m-thick lava succession rests on the 61 Ma Urbjerget Formation, is intercalated with volcaniclastic sediments, and has 57 Ma ⁴⁰Ar/³⁹Ar stepwise degassing ages. It is part of the Milne Land Formation, the first of the major flood basalt formations in East Greenland, and the result of plume impingement of the Kangerlussuaq area in East Greenland during the initial stages of continental breakup. The Ti-rich picrites have relatively primitive compositions and contain Mn- and Ni-rich olivine up to Fo₈₈. Intermediate to high ⁸⁷Sr/⁸⁶Sr_i (0.7034–0.7044) and low Pb isotopic compositions reflect 4–11% crustal contamination, whereas the initial εNd (+4 − +5) and ¹⁸⁷Os/¹⁸⁸Os ratios (0.121–0.129) overlap with recent Icelandic basalts and appear little affected by contamination processes. The mantle source of the Ti-rich picrites contained garnet and was pyroxene-rich and similar to that of later low-Si alkaline basalts. The Ti-rich picrites of the PAWB, similar to other Ti-rich melts of the Kangerlussuaq region, represent analogies of MgO-rich and variably TiO₂-enriched melts from pyroxene rich sources of traditionally accepted mantle plumes like Hawaii. [ABSTRACT FROM AUTHOR]