Palaeomagnetism of the giant dykes of Tugtutoq and Narssaq Gabbro, Gardar· Igneous Province, South Greenland

Abstract

The earliest phases of the last major episode of magmatism within the Precarnbrian Gardar Igneous Province of South Greenland are NE-SW trending giant dykes. Palaeomagnetic samples from seven localities within the Hviddal syenite giant dyke (Rb-Sr whole rock isochron 1175±9 m.y.) yield a palaeomagnetic pole at 215°E, 33°N (k = 38, A,s = 9.9"J. Thirteen sites from gabbro giant dykes (<1175 m.y., >1168m.y.) give a palaeomagnetic pole at 226°E, 42°N (k = 30, A,s = 9.5°), and four sites from the Narssaq gabbro of comparable age give a pole at 225°E, 32°N (k= 97, A,s = 9.9"). All sites have the same polarity although eight additional sites suggest that a secondary intermediate direction was occupied by the magnetic field at intervals with comparable intensity to the main field. The palaeomagnetic pole positions define an easterly apparent polar movement and are consistent with poles of similar age from the Superior craton of North America on the pre-drift reconstruction.