Magnetic fabrics as constraints on the kinematic history of a pre-tectonic granitoid intrusion, Kristineberg, northern Sweden

Outcrop-scale correlations of deformation fabrics with low-field anisotropy of magnetic susceptibility (AMS) measurements revealed a two-stage structural evolution of the pre-tectonic, Palaeoproterozoic Viterliden intrusion in the Skellefte District, Sweden. The first deformation event reflected ∼N–S compression during basin inversion, and comprised reverse dip-slip shearing along major ∼E–W faults, whereas the low-strain lenses in between experienced penetrative deformation with a component of NE–SW elongation along the main foliation. This event is largely responsible for the present structural geometry regionally and locally, and also for the magnetic fabric of the rocks. In particular, the sub-vertical maximum principal susceptibility axes (Kmax) within the high-strain zones are related to early dip-slip deformation, and were virtually unaffected by subsequent dextral strike-slip reactivation, which is recorded by sub-horizontal rock lineations. The strike-slip deformation reflects ∼E–W bulk shortening and may regionally be correlated with reverse faulting along a ∼N–S trending major shear zone east of the study area.

Research highlights
► Combining AMS and rock fabrics at outcrop-scale was successfully used to distinguish fabric elements derived from separate deformation events within a pre-tectonic granitoid intrusion
► In high-strain zones, the magnetic fabric was governed by the early deformation, and was only partially, if at all, modified by the subsequent tectonic events
► In low-strain lenses, both the AMS signature and the rock fabric developed during one single deformation even