Absolute paleointensity at 1.27 Ga from the mackenzie dyke swarm (Canada)

Abstract

[1] Paleointensity studies have been conducted on 6 mafic dykes from the 1270 Ma Mackenzie swarm in the Slave Province (Canada). The mean direction of the characteristic magnetization coincides with results of an earlier study in which the primary origin of the magnetization was established on the basis of a contact test. High unblocking temperatures, magnetic mineralogy, and grain-size experiments suggest that the magnetization is dominated by pseudo-single domain or single domain grains of magnetite. Paleointensity experiments were conducted with a specially designed oven, using a revised version of the Thellier-Coe method. Thirteen successful determinations of paleointensity were obtained for 4 dykes. The paleofield estimates vary between 4.3 and 22.1 μT, yielding virtual dipole moments (VDMs) between 1.3 ± 0.2 and 4.5 ± 0.9 × 1022 Am2. These new results increase the number of low field determinations during the Precambrian, which largely dominate the database with an averaged field of 3.1 ± 2.5 × 1022 Am2. They also emphasize the importance of additional studies to understand the differences with the strong paleointensities obtained using new techniques. Copyright 2006 by the American Geophysical Union.