Paleomagnetism and U-Pb geochronology of diabase dyke swarms of Minto block, Superior Province, Quebec, Canada

In the first collaborative study of paleomagnetism and precise U-Pb geochro nology in the Minto block of the Superior Province, mafic dyke swarms with three widely divergent paleomagnetic signatures and isotopic ages have been identified. The 2505 +/- 2 Ma Ptarmigan dykes trend north to northeast and have a virtual geomagnetic pole at 42 degrees S, 220 degrees E, similar to that of 2473-2446 Ma Matachewan dykes of the southern Superior Province. T he ca. 2230 Ma Maguire dykes trend west to northwest and yield a paleopole at 9 degrees S, 267 degrees E, similar to those for 2216(-4)(+8) Ma Sennete rre dykes and 2217-2210 Ma Nipissing sills of the southern Superior and Sou thern provinces, respectively. The 2209 +/- 1 Ma Klotz dykes trend west-nor thwest, but do not carry a consistent magnetization direction. Finally, 199 8 +/- 2 Ma Minto dykes of west-northwest to northwest trend, identical in a ge to the 1998 Ma +/- 2 Ma Purtuniq ophiolite of the Cape Smith Belt, have a paleopole at 38 degrees N, 174 degrees E. The similarity of paleopoles fo r the ca. 2.23-2.21 Ga Maguire dykes of the Minto block, Senneterre dykes o f the southern Superior, and Nipissing sills of the Southern Province demon strates that these regions were in their present relative latitudes and ori entations at that time. Likewise, the similarity of the Ptarmigan virtual g eomagnetic pole and the Matachewan paleopole suggests little relative latit udinal movement or rotation of the two regions since ca. 2.5 Ga. The Maguir e, Senneterre, and Klotz dykes form a roughly radiating pattern and may rep resent one quadrant of a giant radiating dyke swarm centred southeast of Un gava Bay, whose focus marks the location of a mantle plume responsible for ca. 2.22 Ga breakup along the eastern margin of the Superior Province. If s o, the coeval Nipissing sills that intrude sedimentary rocks of the Huronia n Supergroup of the Southern Province may have been fed laterally by Sennet erre dykes from the Ungava plume centre.