Palæomagnetic Results from Northern Canada suggesting a Tropical Proterozoic Climate

Abstract

THE Coppermine and September Mountains, in the north-central District of Mackenzie, North-west Territories of Canada, are composed of a thick succession of tholeiite basalt flows. Directions of natural remanent magnetization were measured on 51 oriented samples from 24 sites (Fig. 1). The sites represent 24 of the more than 60 separate flows occurring in a vertical thickness of more than 5,000 ft. The flows dip from 0° to 5° north in the area sampled. Two potassium/argon whole rock age determinations on flow rocks, made in the Isotope and Nuclear Geology Section of the Geological Survey of Canada (Wanless, private communication), gave an average age of 1,150 m.y. with a probable error of ± 100 (calculated as two standard deviations from the mean). This places the age of extrusion of the flows in upper middle Proterozoic time. The lavas conformably overlie dolomite of the Hornby Bay Group, and in places thin sandstone bands are intercalated between the flows. A sample from a red sandstone intercalation gives a direction of D = 236, I = +24, which is similar to that of the flows.