The Petrochemistry and Paleomagnetism of the Molson Dikes, Manitoba

Northeasterly trending, tholeiitic, low-alkali basaltic dikes which cut the Archean rocks of northeastern Manitoba have yielded a paleomagnetic pole at 114°W, 28°N, α 95 = 12°. The material from nine sites was normally magnetized, and from one site, reversely magnetized. Potassium–argon age determinations suggest that the dikes were magnetized during late Aphebian. They may have been magnetized at the time of intrusion. Strongly differentiated dikes show intense and variable deuteric alteration, which is interpreted to be the cause of within-site dispersion of NRM. However, strong NRM is related to high contents of opaques regardless of the degree of alteration. Aphanitic dikes of low magnetite content and exhibiting minimal magmatic differentiation usually record moderate magnetic intensities and good groupings.