Effect of low-temperature treatments on pseudo-Thellier paleointensity determination

In paleointensity determination on multidomain (MD) magnetite, demagnetization is always easier than restoring remanence in companion acquisition steps. As a result, paleointensity results follow a convex-down curve on the Arai plot. In an attempt to overcome this problem, the effect of systematic low-temperature demagnetization (LTD) on pseudo-Thellier results was examined. LTD was applied not only to the initial anhysteretic remanent magnetization (ARM, simulating natural remanent magnetization or NRM) but also after each partial anhysteretic remanent magnetization (pARM) acquisition step. Three practical benefits of systematic LTD were discovered. (1) LTD-treated pseudo-Thellier results always yielded more accurate intensity values regardless of grain size and sample lithology. (2) LTD improved the behavior of MD magnetite in paleointensity determination, although not as much as for single-domain and pseudosingle-domain grains. (3) An unanticipated bonus was a more even distribution of data points on the Arai plot, resulting from the fact that LTD causes a shift of points toward the upper end of the Arai curves. Constructing a three-dimensional map of the distributions X and XLTD was successful in quantitatively explaining behavior on the Arai plots.