Preliminary palaeomagnetic results of an Archaean dolerite dyke of west Greenland: geomagnetic field intensity at 2.8 Ga

• Published in: Geophysical Journal International
• Main Authors: Morimoto, Chiyo, Otofuji, Yo-ichiro, Miki, Masako, Tanaka, Hidefumi, Itaya, Tetsumaru
• Format: Text
• Language: English
• Published: Oxford University Press 1997
• Subjects: Articles; Greenland; Nuuk
• Online Access: http://gji.oxfordjournals.org/cgi/content/short/128/3/585; https://doi.org/10.1111/j.1365-246X.1997.tb05320.x

The geomagnetic field intensity during Archaean times is evaluated from a palaeomagnetic and chronological study of a dolerite dyke intruded into the 3000 Ma Nuuk Gneisses at Nuuk (64.2°N, 51.7°W), west Greenland. Plagioclase from the dolerite dyke yields a mean K-Ar age of 2752 Ma. Palaeomagnetic directions after thermal demagnetization of the dyke and the gneiss reveal a positive baked-contact test, indicating that the high-temperature-component magnetization of the dyke is primary. Thellier experiments on 12 dyke specimens yield a palaeointensity value of 13.5±4.4 μT. The virtual dipole moment at ca. 2.8 Ga is 1.9±0.6 × 1022 Am2, which is about one-quarter of the present value. The present study and other available data imply that the Earth's magnetic field at 2.7 ∼ 2.8 Ga was characterized by a weak dipole moment and that a fairly strong geomagnetic field similar to the present intensity followed the weak field after ca. 2.6 Ga.