Magnetization of Keweenawan rocks near Duluth, Minnesota

Remanent magnetization measurements on 200 oriented samples from the Keweenawan gabbro, diabase, and associated rocks in the Duluth area show a clustering of directions west-northwest and downward. Gabbro samples magnetized in this direction usually have Q, the ratio of remanent to induced magnetization, up to five, whereas other gabbro samples have larger Q. Diabase shows no such generalization. Remanent magnetization is important in all rocks studied. Q ranges from 0.3 to 75, but is less than 1.0 in only 15 samples. Volume magnetic susceptibility averages range from 0.3 × 10^-3 to 6.0 × 10^-3. There is no apparent correlation between magnetic susceptibility and the direction of remanent magnetization. Average directions of remanent magnetization indicate a Keweenawan geomagnetic north pole at latitude 30° to 34° N, longitude 175° to 180° W.