Non-linear sampling of Preisach distributions: A method to examine strong remanence carriers with coexisting MD magnetite

Abstract:

Rocks containing large soft magnetic components together with high-coercivity remanence carriers are difficult to analyze by hysteresis loops, first-order reversal curves, or other in-field measurements because the induced magnetization in moderate fields outweighs the remanent component, making it difficult to precisely recover the latter. However, strong remanent aeromagnetic anomalies originating from coarse-grained rocks that contain abundant multidomain magnetite, such as the Mt. Harcus intrusions (Musgrave Province, South Australia), attest that such rocks can also contain strong remanent components. To better identify and characterize thisremanent component it is useful to measure the Preisach distribution in the remanent region using field steps adapted to the distribution of the coercive fields of the sample.

Measuring remanence directly confers a variety of advantages, including higher sensitivity to remanent components as compared to in-field measurements. The technique allows the quantification of total remanence carried by individual components in samples with complex mineralogies. Moreover, magnetostatic interaction between induced and remanent magnetization components is avoided and does not distort the inferred remanence distribution. We provide several examples for this measurement approach and show how it can be used to distinguish multiple remanence fractions and their interactions.