TY - JOUR
T1 - Rock-magnetic properties of single zircon crystals sampled from the Tanzawa tonalitic pluton, central Japan
AU - Sato, Masahiko
AU - Yamamoto, Shinji
AU - Yamamoto, Yuhji
AU - Okada, Yoshihiro
AU - Ohno, Masao
AU - Tsunakawa, Hideo
AU - Maruyama, Shigenori
N1 - Funding Information:
We thank Tetsu Kogiso for help with XRF experiments at Kyoto University. This study was performed under the cooperative research program of Center for Advanced Marine Core Research (CMCR), Kochi University . This work was supported by JSPS Grant-in-Aid for Challenging Exploratory Research No. 26610142.
Publisher Copyright:
© 2015 Sato et al.
PY - 2015/12/22
Y1 - 2015/12/22
N2 - This paper reports on the rock-magnetic properties of single zircon crystals, which are essential for future work establishing the reliable paleointensity method using single zircon crystals. Zircon crystals used in this study were sampled from the Nakagawa River, which crosses the Tanzawa tonalitic pluton in central Japan. Rock-magnetic measurements were conducted on 1037 grains of zircons, but many of these measurements are below the limits of the sensitivity of the magnetometers employed. Isothermal remanent magnetizations (IRMs) of 876 zircon crystal are below the practical resolution of this study; we infer that these crystals contain no or only minute quantities of ferromagnetic minerals. The other zircon crystals contain enough magnetic minerals to be measured in the DC SQUID magnetometer. For 81 zircon crystals, IRM intensities (M IRM) are larger than 4∈×∈10-12 Am2, while natural remanent magnetization (NRM) intensities (M NRM) are below 4∈×∈10-12 Am2, indicating that these crystals are inappropriate for the paleomagnetic study. For the samples that had values of M NRM∈ ∈4∈×∈10-12 Am2 and M IRM∈ ∈4∈×∈10-12 Am2 (80 zircons), combining the rock-magnetic parameter, we proposed the sample-selection criteria for future study of paleointensity experiments using single zircon crystals. In the case that the samples had high coercivity (B c) values (>10 mT) or high M NRM/M IRM values (>∼0.1), main remanence carriers are probably pyrrhotite and these samples are inappropriate for the paleointensity study. In the case that the samples had low B c values (<10 mT) and low M NRM/M IRM values (<∼0.1), main remanence carriers seem to be nearly pure magnetite with pseudo-single-domain grain sizes, and these samples are expected to appropriate for the paleointensity study. Total thermoremanent magnetization (TRM) acquisition experiments were also carried out for 12 samples satisfying the above criteria. The TRM intensity was comparable with that of NRM, and a rough estimation of the paleointensity using NRM/TRM ratios shows field intensities consistent with the average geomagnetic field intensity at the Tanzawa tonalitic pluton for last 5 Myr.
AB - This paper reports on the rock-magnetic properties of single zircon crystals, which are essential for future work establishing the reliable paleointensity method using single zircon crystals. Zircon crystals used in this study were sampled from the Nakagawa River, which crosses the Tanzawa tonalitic pluton in central Japan. Rock-magnetic measurements were conducted on 1037 grains of zircons, but many of these measurements are below the limits of the sensitivity of the magnetometers employed. Isothermal remanent magnetizations (IRMs) of 876 zircon crystal are below the practical resolution of this study; we infer that these crystals contain no or only minute quantities of ferromagnetic minerals. The other zircon crystals contain enough magnetic minerals to be measured in the DC SQUID magnetometer. For 81 zircon crystals, IRM intensities (M IRM) are larger than 4∈×∈10-12 Am2, while natural remanent magnetization (NRM) intensities (M NRM) are below 4∈×∈10-12 Am2, indicating that these crystals are inappropriate for the paleomagnetic study. For the samples that had values of M NRM∈ ∈4∈×∈10-12 Am2 and M IRM∈ ∈4∈×∈10-12 Am2 (80 zircons), combining the rock-magnetic parameter, we proposed the sample-selection criteria for future study of paleointensity experiments using single zircon crystals. In the case that the samples had high coercivity (B c) values (>10 mT) or high M NRM/M IRM values (>∼0.1), main remanence carriers are probably pyrrhotite and these samples are inappropriate for the paleointensity study. In the case that the samples had low B c values (<10 mT) and low M NRM/M IRM values (<∼0.1), main remanence carriers seem to be nearly pure magnetite with pseudo-single-domain grain sizes, and these samples are expected to appropriate for the paleointensity study. Total thermoremanent magnetization (TRM) acquisition experiments were also carried out for 12 samples satisfying the above criteria. The TRM intensity was comparable with that of NRM, and a rough estimation of the paleointensity using NRM/TRM ratios shows field intensities consistent with the average geomagnetic field intensity at the Tanzawa tonalitic pluton for last 5 Myr.
KW - Paleointensity
KW - Rock-magnetism
KW - Tanzawa tonalitic pluton
KW - Zircon
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U2 - 10.1186/s40623-015-0317-9
DO - 10.1186/s40623-015-0317-9
M3 - Article
AN - SCOPUS:84942115920
SN - 1343-8832
VL - 67
JO - Earth, Planets and Space
JF - Earth, Planets and Space
IS - 1
M1 - 150
ER -