TSK 11 Göttingen 2006 Schmidt et al. Separation of magnetic sub- fabrics by high-field, low- temperature torque measure- ments Poster Volkmar Schmidt1 Ann M. Hirt1 Pas- cal Rosselli1 The anisotropy of magnetic susceptibil- ity (AMS) can serve as a good indicator of strain in deformed carbonate rocks with diamagnetic susceptibility (Owens and Rutter 1978; de Wall 2000). How- ever, the magnetic fabric due to the diamagnetic carbonate minerals is usu- ally very weak and interpretation of the AMS in these rocks is often compli- cated by the presence of paramagnetic and ferromagnetic phases which over- print the diamagnetic subfabric. For this reason contributions from ferromag- netic and paramagnetic minerals to the AMS should be separated for a reliable interpretation of the AMS. Ferromag- netic contributions to the AMS can be separated by high-field measurements, using a torque magnetometer (Martin- Hernandez and Hirt 2001). The re- maining paramagnetic and diamagnetic contributions can be discriminated by their different temperature dependen- cies. The paramagnetic susceptibility increases as an inverse function of tem- perature, whereas the diamagnetic part remains constant. Altogether, AMS measurements at high fields and low temperatures allow for the discrimina- tion of all three subfabrics. Test measurements with the high-field torque magnetometer at liquid nitrogen temperature were performed. It is possi- ble to keep the specimens at low temper- ature over the measurement period us- 1 Institute of Geophysics, ETH Zurich, 8093 Zurich, Switzerland ing a cryostat. The main problem is the suppression of mechanical disturbances during the measurement so that the sen- sitivity of the instrument is retained. The torque of paramagnetic minerals increases strongly at low temperature which results in an amplification of the paramagnetic subfabric. The quantita- tive separation of diamagnetic and para- magnetic subfabric is under investiga- tion. The result is promising when there is a significant diamagnetic signal. References De Wall H, Bestmann M & Ullemeyer K (2000) Anisotropy of diamagnetic suscepti- bility in Thassos marble: A comparison be- tween measured and modeled data. J Struct Geol 22, 1761–1771 Martin-Hernandez F & Hirt AM (2001) Sep- aration of ferrimagnetic and paramagnetic anisotropies using a high-field torsion mag- netometer. Tectonophysics 337, 209–221 Owens WH & Rutter EH (1978) The develop- ment of magnetic susceptibility anisotropy through crystallographic preferred orienta- tion in a calcite rock. Phys Earth Planet Inter 16, 215–222 1