Experimental and numerical modeling of IRM rotation in deformed synthetic samples

Abstract

The effect of strain upon isothermal remanent magnetization (IRM) carried by hematite particles embedded in a plasticine matrix has been investigated. Magnetized artificial hand samples were deformed by simple coaxial shortening. After deformation, the hand-samples were cut into 8–15 specimens and each specimen's IRM measured. Hence a mean IRM direction was obtained for each shortening step. The main results are: (1)|When the initial direction of IRM is parallel to the shortening axis ( λ 3) the hand-sample mean IRM stays parallel to λ 3 during deformation. However, individual magnetization directions are deflected towards the flattening plane, and thus the specimen directions are scattered by strain. This is accompanied by a significant decrease of magnetization intensity. (2)|In contrast, when the initial direction of IRM is perpendicular to λ 3, the shortening results in a clustering of specimen magnetization directions, the mean direction being unchanged. This is accompanied by a slight increase of magnetization intensity. (3)|In all other cases, where initial IRM direction makes an intermediate angle with shortening direction, deformation induces a deviation of each specimen IRM toward the flattening plane. This results in an overall deflection of hand-sample mean IRM. The amount of rotation increases with strain intensity. Changes of grouping and intensity depend on the initial angle between IRM and λ 3, defining a continuum in behavior between IRM directions being either parallel to λ 3 or perpendicular to λ 3. Finally, it is shown that all the experimental changes in IRM due to deformation (direction, grouping, intensity) can be modeled by a passive marker rotation of hematite planar particles.