On the resolution of multivectorial remanences

Low-temperature demagnetization (LTD) promotes single-domain (SD)-like alternating field (AF) and thermal demagnetization properties of anhysteretic remanent magnetization (ARM) and thermoremanent magnetization (TRM), by eliminating low-coercivity or low-unblocking-temperature fractions of remanence. We have investigated the effectiveness of LTD in improving the independence of partial ARMs (pARMs). Independence of pARMs and of partial TRMs (pTRMs) is crucial because multivectorial directional analyses and paleointensity determinations are otherwise compromised. In normalized vector plots of AF demagnetization of orthogonal pARMs, LTD-treated samples showed universal improvement in the degree of independence. The greatest improvement was for synthetic SD and pseudo-single-domain magnetites and natural lake sediments. On the other hand, independence barely improved for synthetic multidomain magnetite, granites, and gabbros. In general, LTD provides a better resolution of superimposed vectors in multicomponent remanence. The direction of the original ARM (corresponding to primary NRM in nature) is perfectly recovered. However, the pARM (the overprint) is not perfectly resolved, especially for overprinting coercivities <40 mT, where the deviation in inclination is 10° or more.