The detection of single-domain greigite (Fe3S4) using rotational remanent magnetization (RRM) and the effective gyro field (Bg): mineral magnetic and palaeomagnetic applications |
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| Authors: | Ian F Snowball |
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| Institution: | Laboratory for Palaeomagnetism, Geological Survey of Finland;, 02150 Espoo, Finland. E-mail: ian.snowball@geol.lu.se |
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| Abstract: | The intensity of rotational remanent magnetization (RRM) acquired by single-domain greigite at a rotation frequency of 5 rps was combined with measurements of anhysteretic remanent magnetization (ARM) to calculate the effective biasing field ( Bg ) that produced the RRM. Samples of single-domain greigite had Bg values between -137 and -84 μT, and a MDFRRM of c. 80 mT. By contrast, a suite of natural and synthetic ferrimagnetic iron oxide samples, including single-domain magnetite and y Fe3O4 tape particles, acquired Bg values between -3 and -14 μT, and MDFRRM ranged between 43 and 68 mT (when RRM was acquired). Multidomain magnetite did not acquire a RRM. Bg values at 5 rps were calculated from previously published data for magnetite particles of different grain sizes, which revealed a minimum Bg value of -24 μT and a MDFRRM of 57 mT for the finest fraction (0.2-0.8 μm in diameter). In a geological example, measurements of Bg and MDFRRM were used to detect the presence of greigite in a 4 m long Late Weichselian sediment core. Variations in inclination, declination and the intensity of the natural remanent magnetization (NRM) correlate with changes in magnetic mineralogy. |
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| Keywords: | Key words: greigite magnetite palaeomagnetism rock magnetism rotational remanent magnetization sediments |
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