DeformAMS: A simple toolbox for modelling magnetic fabric evolution during rock deformation

The magnetic fabric, studied mainly by means of anisotropy of magnetic susceptibility (AMS), has become one of the well-established, fast, and reliable rock fabric proxies applied in many branches of Earth sciences. The magnetic fabric of rocks reflects the crystallographic or shape preferred orientation of all rock-constituent mineral grains; each mineral grain contributes to the overall fabric according to its single-grain anisotropic properties and its orientation.

Because magnetic fabric is very sensitive to strain, a simple tool box is presented to model its evolution as a results of rock deformation. The toolbox works with a set of uniformly distributed model particles deformed following the so-called line/plane model which assumes that the particles behave as if they formed lines or planes in the deforming rock matrix; their shapes do not change in response to the imposed deformation but their orientation does. The pre-deformational and deformational magnetic fabrics are considered, both having originated through combined pure shear and simple shear acting in the pre-defined directions.

The resultant magnetic fabric tensor is calculated by integrating the combined contribution of the entire set of modelled particles. The results are presented in terms of the principal AMS directions, degree of anisotropy, and shape of anisotropy ellipsoid. The presented toolbox is an integral part of Anisoft6 software which enables the instant visualization of how magnetic fabric gradually changes as a function of progressive deformation.

The research was in partially conducted within the research plan RVO 67985831 of the Institute of Geology of the Czech Academy of Sciences.