Paleomagnetism and U-Pb geochronology of Franklin dykes in High Arctic Canada and Greenland: a revised age and paleomagnetic pole constraining block rotations in the Nares Strait region

U-Pb baddeleyite ages and paleomagnetic poles obtained for dykes on Devon Island and Ellesmere Island in the Canadian Arctic and the Thule region of Greenland show that they are associated with the Franklin magmatic event. This study is the only one devoted to Franklin igneous rocks where a primary paleomagnetic remanente and U-Pb age have been obtained from the same rocks. Ages from this study range from 721 to 712 Ma, but paleomagnetic directional data show no clear age progression. The paleomagnetic poles from each of the two regional subsets are significantly different at the 95% confidence level from paleomagnetic results previously published for the Franklin event in the CanadianShield. The difference in the pole locations can be accounted for, to first approximation, by a simple model of early Cenozoic block rotations among the North American plate, Greenland, and a hypothesized ancient microplate comprising Ellesmere, Devon, Cornwallis, and perhaps Somerset islands. A new grand-mean paleopole for the Franklin event, including restoration of Greenland and the proposed 'Ellesmere microplate' to North America, is located at (8.4°N, 163.8°E, [A.sub.95] = 2.8°, N = 78 sites) and is a key pole for Neoproterozoic supercontinent reconstructions. Des ages U-Pb, determines sur de la baddeleyite, et des poles paleomagnetiques obtenus de dykes des files de Devon et d'Ellesmere, dans fArctique canadien, et de la region de Thule au Groenland, montrent que ces dykes sont associes a fevenement magmatique de Franklin. La presente etude est la seine consacree aux roches ignees de Franklin ou une remanente paleomagnetique primaire et des ages U-Pb ont ete obtenus des memes roches. Les ages dans cette etude varient de 721 a 712 Ma, mais les donnees sur les directions paleomagnetiques ne montrent aucune progression Claire de l'age. Les poles paleomagnetiques de chacun des deux sous-ensembles regionaux different de maniere significative, au niveau de confdance 95 %, des resultats paleomagnetiques publies anterieurement pour l'evenement de Franklin dans le Bouclier canadien. La difference d'emplacement des poles peut etre expliquee, en une premiere approximation, par un modele simple de rotations de blocs, au Cenozoique precoce, entre la plaque Nord-americaine, le Groenland et une ancienne plaque hypothetique qui comprenait les files d'Ellesmere, de Devon, de Cornwallis et peut-etre de Somerset. Un nouveau paleopole de grande moyenne pour l'evenement Franklin, incluant la restoration du Groenland et de la << microplaque d'Ellesmere >> proposee a l'Amerique du Nord, est situe a (8,4[degre]N, 163,8[degre]E, [A.sub.95] = 2,8[degre], N = 78 sites) et constitue le pole cle pour les reconstructions du super continent au Neoproterozoique. [Traduit par la Redaction]
Introduction Precisely dated rocks with well-defined paleomagnetic poles are scarce in the Proterozoic record, yet are critical for reconstructing the past positions of continents and correlating what are today the [...]