On the Pseudo-Thellier Method for Single-Domain Non-Interacting Particles. Theory and Experiment

The pseudo-Thellier method was numerically simulated based on a rigorous solution of kinetic equations for uniaxial, chaotically oriented, non-interacting single-domain particles. Laboratory experiments were performed to determine the relative paleointensity Bдр with thermoremanent magnetization (TRM) created on samples of igneous rocks in random fields Bсл. The domain structure of grains of these samples varies from single- to multi-domain. Both theoretical and experimental pseudo-Arai diagrams can be divided into two quasi-rectilinear sections, one of which is located in a relatively low-coercivity region Bc < 40–50 mT, and the second — at higher amplitudes of the alternating field (AF). Determinations of the relative paleointensity Bдр on igneous rocks bearing TRM, performed on low-coercivity segments of pseudo-Arai diagrams, give quite satisfactory results with a linear correlation coefficient R = 0.8 between the true field Bсл and Bдр, determined using the pseudo-Thellier method. It is shown that when taking into account thermal fluctuations for relatively magnetically soft and small particles (which corresponds to low blocking temperatures), there is a significant difference between the coercive force of a particle Bp and the actual field of its magnetization (demagnetization). The main conclusion of the work is that the application of the pseudo-Thellier method to igneous rocks is a promising direction, and its development in both methodological and practical aspects can bring interesting results, especially when applied to samples that are unstable to magnetomineralogical changes in the process of applying the classical Thellier method.

anhysteretic remanent magnetization, thermoremanent magnetization, kinetic equations, pseudo-Thellier method, pseudo-Arai diagrams