Abstract

Some of the red beds of the Seal Group contain at least two CRM (chemical remanent magnetization) components. The dominant one has a direction of 275°, +05 °(pole position 205 °E, 05 °N). The less pronounced component has a direction which is about 55 °clockwise from this. It is suggested that the dominant (westerly) component is the younger one and was developed after the block containing these rocks was rotated clockwise.The igneous rocks of the Seal and Croteau Groups are reversely magnetized relative to the red beds and yield a pole (152 °E, 05 °N) about 50° away from that indicated by the major component of the red beds. The magnetization of the igneous rocks is thought to contain a primary TRM (thermoremanent magnetization) but the igneous pole is 65 °of arc away from poles derived from rocks of similar age in the Superior Province. If, however, a correction of 55 °rotation (as suggested by the red-bed results) is applied to the block, the igneous pole then lies in the southern hemisphere (197 °E, 22 °S) close to poles for rocks of similar age from the Superior Orogen. It is then suggested that the primary magnetization of the igneous rocks was acquired before rotation. Because of its pole position, it appears that the dominant CRM (post-rotation) was acquired less than 400 m.y. after the initial magnetization of the igneous rocks. This places an upper limit to the interval of time during which the rotation occurred. It is suggested that the rotation is perhaps related to early Grenvillian orogenic and thermal events (1200–1500 m.y.).Paleomagnetic evidence when coupled with geological evidence suggests that not only was the N.E. Grenville Orogen rotated, but that in the interval 1550–1200 m.y. ago, the paleopole relative to this part of the crust (and to the Superior) underwent an excursion, referred to as the "Grenville Loop", deep into the Southern hemisphere.

You do not currently have access to this article.