Paleointensity determination, magnetic domain structure, and selection criteria

This special section is focused on the impact of Kittel's theory of magnetic domains on rock magnetism, and this paper is focused on the implications fur paleointensity determinations. Absolute paleointensity determination is based on specific properties of thermoremanent magnetizations (TRMs), mainly the linear dependence of a TRM's intensity on the inducing field and the additivity and independence of partial TRMs. These properties are exhibited by populations of noninteracting single-domain (SD) grains but not by populations of multidomain grains. The situation is more complex in the pseudo-single-domain population, the most common one in natural rocks usable for paleointensity studies, which sometimes exhibit SD-like behavior but not always. If the experiments were restricted to SD rocks, it would not be possible to find enough outcrops to have the spatial and temporal resolution needed for interpretation of the data in terms of geodynamo. However, as paleointensity determination is very time consuming, a preselection of suitable samples is necessary. A new procedure will be proposed using a direct test of partial TRM's properties with a fully automated experiment, fast to implement.