Thermal enhancement of magnetic fabrics in high grade gneisses

Abstract

The orientation-distributions of AMS and AARM ellipsoids are non-coaxial in the Kapuskasing Zone granulites. AARM is due to the preferred orientation of magnetite which mostly postdates the silicate fabric. The AMS orientation-distribution combines susceptibility anisotropies of magnetite and the silicates. Whereas heating does not increase the bulk susceptibility, it does improve the definition of the orientation-distributions of both AMS and AARM. However, the orientation-distribution of AARM is most enhanced and therefore post-heated samples emphasize the magnetite subfabric. Thus, heating does not clarify the interpretation of the silicate fabric in this study. However, it does change the samples' AMS fabric in such a way as to reveal the magnetite subfabric which can only otherwise be detected by more tedious AARM measurements.