In the Archean Superior Province, the Nipigon Embayment, in the area of Lake Nipigon north of Lake Superior, is covered by MidProterozoic sediments intruded by Keweenawan diabase sills. It has been interpreted as a failed arm of the ca. 1100 Ma Keweenawan rift. Six new heat flow values in this area show that the region of low heat flow associated with the Keweenawan rift in Lake Superior extends northwards along the western margin of the Nipigon Embayment. The average heat flow in the Nipigon area (39 ¿ 5 mWm-2) is only slightly lower than that of the adjacent western Superior Province (42 ¿ 8 mWm-2), indicating that the volume of Keweenawan mafic intrusives in the Nipigon crust is small.