Baddeleyite and zircon U–Pb ages from the Kærven area, Kangerlussuaq: Implications for the timing of Paleogene continental breakup in the North Atlantic

Abstract

We report U–Pb zircon and baddeleyite age results for two mafic units in the Kangerlussuaq area which are part of the Paleogene East Greenland igneous province; the Kangerlussuaq macrodyke, which represents a feeder to some flood basalts, and the nearby Kærven Gabbro. Baddeleyite from the macrodyke yielded a concordant age of 54.7 ± 0.4 (2 σ) Ma and this is among the most precise age determinations from the province. This age is interpreted to reflect the time of emplacement. The macrodyke belongs to a swarm of dykes emplaced perhaps in a failed arm during continental rifting, and the age predates the completion of continental breakup at the end of emplacement of the Plateau Basalts of the East Greenland eruption sequence. Geochemically the macrodyke is correlated with the Milne Land Formation lavas. The magma experienced slight crustal contamination. Based on the age and geochemistry of the macrodyke, the age of the Skaergaard intrusion and Skrænterne Formation lavas, an age span of 1–2 Ma is confirmed for the extrusion of the entire Plateau Basalts. U–Pb analysis of zircon from the Kærven Gabbro yields an age of 53.0 ± 0.3 (2 σ) Ma. The Kærven Gabbro was intruded after extension had ceased in the area and we suggest that the post plateau basalt magmatism did not take place at a distinct later time, but instead that igneous activity continued for some time at a lower rate. Slightly fractionated HREEs indicate that the Kærven Gabbro magma was extracted at relatively shallow levels in the mantle.