Preliminary palaeomagnetic results of an Archaean dolerite dyke of west Greenland: geomagnetic field intensity at 2.8 Ga |
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| Authors: | Chiyo Morimoto Yo-ichiro Otofuji Masako Miki Hidefumi Tanaka Tetsumaru Itaya |
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| Institution: | Department of Earth and Planetary Sciences, Faculty of Science, Kobe University, Kobe, Japan;Department of Applied Physics, Tokyo Institute of Technology, Meguro-ku, Tokyo, Japan;Hiruzen Research Institute Okayama Branch, Okayama University of Science, Okayama, Japan |
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| Abstract: | 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. |
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| Keywords: | Archaean Earth's core geomagnetic field Greenland K-Ar age palaeomagnetism |
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