Multimodal investigation of thermally induced changes in magnetic fabric and magnetic mineralogy

Abstract

SUMMARY Low-field magnetic susceptibility and its anisotropy (AMS) were measured for a suite of sandstone and siltstone samples. AMS orientations measured on two systems (Bartington and Digico) diVered before thermal treatment of the samples but became the same after thermal demagnetization in air to 600°C. Six position measurement schemes for the Bartington system do not eliminate the eVects of specimen inhomogeneity and other errors, whereas 12- and 24-position measurements give good agreement with the Digico anisotropy meter and with the observed petrofabric. Thermal demagnetization from temperatures between 400 and 650°C had the eVect of enhancing both the magnetic susceptibility and AMS. Although the most profound mineralogical change due to heating was the conversion of kaolinite into metakaolin, IRM, XRD,