PALEOMAGNETIC CONSTRAINTS ON THE POSITION OF LAURENTIA FROM MIDDLE NEOPROTEROZOIC TO EARLY CAMBRIAN TIMES

Most published palaeopoles from Laurentia indicate that the craton moved in equatorial regions during much of the Neoproterozoic-Cambrian period. However, recent palaeomagnetic results from the Mackenzie and Wernecke Mountains of northwestern Canada suggest that Laurentia passed over the South Pole sometime close to the Precambrian-Cambrian boundary. By this scenario, the craton remained in equatorial latitudes as part of a Neoproterozoic supercontinent until after the second and last glaciation recorded in Laurentia. It began its ascent to high southern latitudes on or before deposition of the Risky Formation, perhaps following rifting along the eastern margin of Laurentia at similar to 615 Ma. High-latitude-poles related to hematitization might evidence Laurentia's flight to higher latitudes (60-70 degrees S). Hematitization appears to have occurred during a long hiatus in the geological record between deposition of the Risky Formation and the terminal Proterozoic Ingta Formation, and may evidence a final rifting event along the western margin of Laurentia in the late Neoproterozoic. A combined pole from the Ingta and Early Cambrian Backbone Ranges formations forms a bridge to Early Cambrian poles that trend from the Equator to mid-southern latitudes. Except for the excursion of Laurentia over the South Pole in the transition from the Proterozoic to the Phanerozoic Eons, Laurentia seems to have been at latitudes less than 60 degrees S in the period from similar to 900 to 500 Ma.