Fault Rotation of Paleomagnetic Directions in Coppermine River Lavas and their Revised Pole

Abstract

The paleomagnetic pole of a segment of lavas from the upper part of the Coppermine River Group is displaced relative to that previously obtained for the lower part of the group by a 28-degree, counter-clockwise rotation. The inclinations are approximately the same. This segment of lavas is separated from the lower part of the group by a fault zone. Elsewhere where the stratigraphic sequence is continuous, sediments and lavas of the upper part of the group give pole positions, which, although scattered, are in large part close to that of the lower part of the group. Hence, the displaced pole can reasonably be attributed to local rotation along a fault rather than to apparent polar wandering. Recognition of the tectonic rotation of the paleomagnetic pole leads to an interpretation of the faulting in the Coppermine River flows as rift faulting closely following extrusion of the lavas.New Coppermine River pole positions are calculated combining the data previously obtained from the lower part of the Coppermine River Group with that from lavas (4 sites) and sediments (5 sites) from the upper part of the group. The new Coppermine River pole from the lavas is at 02N, 180E and from lavas and sediments combined is at 03N, 182E (dp = 3, dm = 6). The latter is the pole recommended for use. That this is a Coppermine River pole rather than a Mackenzie pole is emphasized with the thought that the various elements of the Mackenzie magmatic events may ultimately resolve into a succession of discrete episodes.