40Ar/39Ar geochronology of Tertiary mafic intrusions along the East Greenland rifted margin: Relation to flood basalts and the Iceland hotspot track

The East Greenland Tertiary Igneous Province includes the largest exposed continental flood basalt sequence within the North Atlantic borderlands. More than ten layered gabbro complexes, including the similar to 55 Ma Skaergaard intrusion, and a large dolerite sill complex are the plutonic equivalents of flood basalts; both lavas and intrusions have been regarded as synchronous with continental breakup at 57-54 Ma. We report ten new ages of the mafic intrusions, determined by 40Ar/39Ar incremental heating experiments, demonstrating that the mafic intrusions formed in two distinct time windows. Only Intrusion II of the Imilik Gabbro Complex, the Skaergard intrusion, and the Sorgenfri Gletscher Sill Complex formed at 57-55 Ma coeval with the eruption of regional flood basalts and continental breakup. Other layered gabbro intrusions at Imilik (Intrusion Iii), Kruuse Fjord, Igtutarajik, Nordre Aputiteq, Kap Edvard Helm, and Lilloise are distinctly younger and formed between 50 and 47 Ma. Plate-kinematic models indicate the axis of the ancestral Iceland mantle plume was located under Central Greenland at similar to 60 Ma and subsequently crossed the East Greenland rifted continental margin. We propose that tholeiitic magmatism along the East Greenland rifted margin largely occurred in three distinct pulses at 62-59 Ma (lavas and dykes), 57-54 Ma (lavas, dykes, sills, and some gabbros) and 50-47 Ma (gabbros, dykes and rare lavas), related to discrete mantle melting episodes triggered by plume impact, continental breakup, and passage of the plume axis, respectively. This model implies northwestward continental drift of Greenland relative to the plume axis by similar to 3.8-5.0 cm/yr between similar to 60 and similar to 49 Ma, consistent with estimates from seismic studies of submerged flood basalts. (C) 1998 Elsevier Science B.V. All rights reserved.