A paleomagnetic study of the layered mafic intrusion at Sept- Iles, Quebec (Canada)

A paleomagnetic study of gabbroic and anorthositic members of the Sept-Iles layered mafic intrusion has isolated a remanence with direction D = 333o, I = -29o (remanence A) and a corresponding pole of 141oE, 20oN. The rocks are cut by numerous diabase dykes of unknown age. The remanence carried by the dykes has direction D = 188o, I = -85o (remanence B) with a corresponding pole of 116oE, 59oS. Another remanence, statistically identical to B (D = 186o, I = -85o), is found at dyke contacts and in the local host rock; its associated pole, 115oE, 61oS, is identical to the one derived from the dykes. This overprint is significantly different from remanance A, and is obviously related to dyke emplacement. The location of the pole derived from remanance A is in excellent agreement with many other Cambrian poles from a variety of locations throughout cratonic North America. The rocks at Sept-Iles have been previously dated radiometrically at 540 Ma. Thus, all evidence indicates that remanence A is an original thermochemical remanent magnetization, acquired during initial cooling of the intrusion in the Cambrian and prior to the emplacement of the dykes.-from Authors