Proterozoic magnetic overprinting of Archaean rocks in the Canadian Superior Province

Abstract

We have measured the various components of natural remanent magnetization (NRM) exhibited by mafic extrusive and intrusive rocks from the Abitibi Subprovince of the Canadian Precambrian Shield. In addition to providing what seems to be a primary Archaean pole for the region, the results testify to three episodes of magnetic ‘overprinting’ at approximately 2,600, 2,100 and 1,800 Myr, respectively. The two earlier episodes coincide with the intrusion of Matachewan and Abitibi diabase dyke swarms, here and elsewhere in the Superior Province. Magnetic overprinting, in these cases, extends far beyond areas of surficial dyke exposure. The third episode postdates magmatic activity in the Abitibi region, but coincides in age with the 1,900–1,700 Myr Hudsonian orogeny in the Churchill and Bear Provinces and the Penokean orogeny in the Southern Province. Although magnetic overprints presumed to be of this age were known previously from Abitibi dykes¹ and Nipissing sills^2–4, our data are the first evidence of a 1,800 Myr magnetic overprinting on a regional scale in the Superior Province.