Precise chronology of large continental flood basalt provinces is pivotal in assessing mantle-melting systematics, volcanic productivity, and lithosphere dynamics of continental rifting and eventual breakup. The catastrophic eruption of many continental flood basalt provinces in less than a few million years, sometimes linked to mass-extinction events through Earth's history, for example, is taken as evidence of the arrival of a mantle plume at the base of the lithosphere (Duncan and Richards, 1991; Hofmann et al., 1997; Renne and Basu, 1991; Storey et al., 1995).

During the Ocean Drilling Program (ODP) Legs 152 and 163, we sampled the early Tertiary volcanic succession forming the seaward-dipping reflector sequence (SDRS), which erupted onto the Southeast Greenland volcanic rifted margin during the breakup of Greenland from northwest Europe (Duncan, Larsen, Allan, et al., 1996; Larsen and Saunders, 1998; Larsen et al., 1994; Saunders et al., 1998). Two transects were originally designed to sample the volcanic succession at ~560 km (63ºN) and ~220 km (66ºN) south of the Greenland-Iceland-Faeroes ridge, the presumed axis of the ancestral Iceland mantle plume (~68ºN) (Fig. 1). The transect at 63ºN was drilled during Leg 152 and comprises a virtually complete section of prebreakup sediments, volcanics (SDRS), and overlying postbreakup sediments (Larsen and Saunders, 1998; Larsen, Saunders, Clift, et al., 1994; Saunders et al., 1998).

The purpose of Leg 163 was to drill into the SDRS and the underlying continental basement at the transect at 66ºN, in addition to complementary sampling at the 63ºN transect. However, because of technical and meteorological difficulties, sampling at the 66ºN transect remained limited (Duncan, Larsen, Allan, et al., 1996). Here we present the results of 14 ⁴⁰Ar-³⁹Ar incremental heating experiments on whole rock and plagioclase from samples recovered at the 63ºN and the 66ºN transect during Leg 163. Including the results of a parallel paleomagnetic study (Duncan, Larsen, Allan, et al., 1996; Hooper et al., Chap. 10, this volume) and the results of Leg 152 geochronology and magnetic stratigraphy (Jolley, 1998; Larsen and Saunders, 1998; Larsen, Saunders, Clift, et al., 1994; Sinton and Duncan, 1998; Vandamme and Ali, 1998; Werner et al., 1998), a virtually complete time frame for pre-, syn-, and postbreakup volcanism for the Southeast Greenland volcanic rifted margin (63ºN-66ºN) is discussed.