Palaeomagnetism of three dyke swarms in Nansen Land, north Greenland (83° N)

Abstract

Three basic dyke swarms of post-Ellesmerian (post-Early Carboniferous) age in Nansen Land (83° N, 43° W) are still not dated numerically, but cross-cutting relationships show Group 1 to be older than Group 2, while Group 3 is the freshest and likely the youngest. Group 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 specimens from 28 sites were investigated palaeomagnetically. Group 1 dykes show unexpected shallow inclinations with a cleaned mean direction of (Dm, Im) = (151°, -5.8°), N = 7, k = 18.5, α95 = 13.9°. They show hydrothermal alterations, some remagnetization by lightning, and the low inclination indicates a low palaeo latitude. The palaeopole is (Plat, Plon) = (8.9° S, 14.0° W) with (dp, dm) = (7°, 14°), and is close to the North American Early Carboniferous mean pole, suggesting a syn- or early late-tectonic dyke injection. The polarity is reverse. Groups 2 and 3 of presumed Cretaceous or Tertiary age show dominantly normal and reverse polarities, respectively. Their mean directions per polarity are well grouped, with (Dm, Im) = (-30.6°, 76.7°), n = 13, k = 191.4, α95 =3.9°, and (Dm, Im) = (133.4°, -76.7°),n = 10, k = 87.5, α95 = 5.9°, respectively. They are antipodal within 95% significance, and combining both swarms gives (Dm, Im) = (-37.5°, 76.8°), n = 23, k = 124.3, α95 = 2.7°, corresponding to a mean pole of (Plat, Plon) = (70.0° N, 185.1° E) with (dp, dm) - (4.7°,5.0°), for which the spline of Late Cretaceous-Tertiary poles for all Greenland indicates 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 American craton, and that the two younger swarms are essentially postdating the opening of Baffin Bay.