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 mT, yielding virtual dipole moments (VDMs) between 1.3 ± 0.2 and 4.5 ± 0.9 Â 10 22 Am 2 . 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 Â 10 22 Am 2 . They also emphasize the importance of additional studies to understand the differences with the strong paleointensities obtained using new techniques.

Palaeomagnetism and geochronology of the Proterozoic dolerite dyke from southwest Greenland: indication of low palaeointensity

“…Macouin et al (2006) together with results from this study. The summarized data are from Morimoto et al (1997), Yoshihara & Hamano (2000, , Sumita et al (2001), Yu & Dunlop (2001, 2002; Smirov et al (2003), Macouin et al (2003), Halls et al (2004), Macouin et al (2006), McArde et al (2004), Thomas & Piper (1995) and Biggin et al (2009). Closed star indicates result from this study and open circles represent secondary magnetization.…”

“…As compared to present-day geomagnetic field, a mean VDM value reported by Macouin et al (2006) from Precambrian rocks (3.1 × 10 22 Am 2 ) is obviously lower in strength. An intensity of the Earth's magnetic field has increased by a factor of 4 between 2.7 and 2.5 Ga (during a period of 200 Myr).…”

“…Fig. 17 shows only those ArchaeanProterozoic VDM data that passed a criteria of Macouin et al (2006), including a double heating technique with pTRM checks. Macouin et al (2006) together with results from this study.…”

“…17 shows only those ArchaeanProterozoic VDM data that passed a criteria of Macouin et al (2006), including a double heating technique with pTRM checks. Macouin et al (2006) together with results from this study. The summarized data are from Morimoto et al (1997), Yoshihara & Hamano (2000, , Sumita et al (2001), Yu & Dunlop (2001, 2002; Smirov et al (2003), Macouin et al (2003), Halls et al (2004), Macouin et al (2006), McArde et al (2004), Thomas & Piper (1995) and Biggin et al (2009).…”

“…Although, some new palaeointensity data have been added (e.g. Smirnov et al 2003;Macouin et al 2006) and some have been reinvestigated (Yoshi- Friend et al (1996). An open circle indicates our sampling locality.…”