Magnetic interaction analysis of basaltic samples and pre-selection for absolute palaeointensity measurements

Abstract

For a successful palaeointensity experiment a sample should only consists of non-interacting single domain (SD) particles. As this cannot be completely guarantied for natural samples we applied two different interaction methods (ΔM plots and FORC-diagrams) on basaltic samples from Fernando de Noronha, Brazil, in order to determine the degree of interaction and estimate their use as a preselection tool for palaeointensity experiments. An independent classification of the samples in terms of SD/MD contribution and the occurrence of partial self-reversals is obtained by rockmagnetic means, Thellier-like experiments and continuous thermal demagnetization. The samples show a variable amount of mean interaction fields, which tends to be higher for samples with partial self-reversal. Nevertheless, high mean interaction fields can also be present in samples of successful palaeointensity experiments with high mean coercivities. This suggests, that the recording potential of a sample depends on the interplay of magnetic interaction and its mean coercivity, i.e. samples of higher mean coercivity resist higher mean interaction fields. As this is difficult to assess by normal rockmagnetic means, interaction measurements, especially the ΔM plot derived parameters ΔM 1 and 2, provide a fast tool for preselection.