PALEOMAGNETISM OF 3 DYKE SWARMS IN NANSEN LAND, NORTH GREENLAND (83-DEGREES N)

Three basic dyke swarms of post-Ellesmerian (post-Early Carboniferous) age in Nansen Land (83 degrees N, 43 degrees W) are still not dated n umerically, but cross-cutting relationships show Group 1 to be older t han Group 2, while Group 3 is the freshest and likely the youngest. Gr oup 1 (the most northerly swarm) strikes N-S; Group 2 NW-SE, and Group 3 (the most southerly swarm) E-W. From more than 200 dykes 234 specim ens from 28 sites were investigated palaeomagnetically. Group 1 dykes show unexpected shallow inclinations with a cleaned mean direction of (Dm, Im) = (151 degrees, -5.8 degrees), N = 7, k = 18.5, alpha(95) = 1 3.9 degrees. They show hydrothermal alterations, some remagnetization by lightning, and the low inclination indicates a low palaeo latitude. The palaeopole is (Flat, Pion) = (8.9 degrees S, 14.0 degrees W) with (dp, dm) = (7 degrees, 14 degrees), and is close to the North America n Early Carboniferous mean pole, suggesting a syn-or early late-tecton ic dyke injection. The polarity is reverse. Groups 2 and 3 of presumed Cretaceous or Tertiary age show dominantly normal and reverse polarit ies, respectively. Their mean directions per polarity are well grouped , with (Dm, Im) = (-30.6 degrees, 76.7 degrees), n = 13, k = 191.4, al pha(95) = 3.9 degrees, and (Dm, Im) = (133.4 degrees, -76.7 degrees), n = 10, k = 87.5, alpha(95) = 5.9 degrees, respectively. They are anti podal within 95% significance, and combining both swarms gives (Dm, Im ) = (-37.5 degrees, 76.8 degrees), n = 23, k = 124.3, alpha(95) = 2.7 degrees, corresponding to a mean pole of (Flat, Pion) = (70.0 degrees N, 185.1 degrees E) with (dp, dm) = (4.7 degrees, 5.0 degrees), for wh ich the spline of Late Cretaceous-Tertiary poles for all Greenland ind icates a palaeomagnetic age of 57 +/- 10 Ma. This pole (in present-day coordinates) is very close to the Late Cretaceous North American pole , in accordance with the fact that Greenland belongs to the North Amer ican craton, and that the two younger swarms are essentially postdatin g the opening of Baffin Bay.