HR: 0800h
AN: GP41A-0857    [Abstracts]
TI: Scope and Examples of Rock Magnetic Investigations in Weak Magnetic Fields Using Multi-Function Kappabridge Set
AU: * Hrouda, F
EM: fhrouda@agico.cz
AF: AGICO Inc., Jecna 29a, Brno, 621 00 Czech Republic
AU: Pokorny, J
EM: jpokorny@agico.cz
AF: AGICO Inc., Jecna 29a, Brno, 621 00 Czech Republic
AU: Suza, P
EM: psuza@agico.cz
AF: AGICO Inc., Jecna 29a, Brno, 621 00 Czech Republic
AU: Pokorny, P
EM: perpok@agico.cz
AF: AGICO Inc., Jecna 29a, Brno, 621 00 Czech Republic
AU: Hirt, A M
EM: hirt@mag.ig.erdw.ethz.ch
AF: Institute of Geophysics, ETH-Hoenggerberg, Zurich, 8093 Switzerland
AU: Tiefenauer, L
EM: Louis.Tiefenauer@psi.ch
AF: Paul Scherrer Institut, Villigen PSI, Villigen, 5232 Switzerland
AB: The investigation of rocks and minerals in low magnetic fields may be a good and relatively inexpensive alternative of the more or less standard high-field rock magnetic techniques. The Multi-Function Kappabridge Set measures the "in phase" susceptibility, the relative changes of the "out of phase" susceptibility and the magnetic loss angle in variable magnetic fields, at variable operating frequencies, and at variable temperatures. The selectable frequencies are 976 Hz, 3,904 Hz and 15,616 Hz. The field ranges are: 2 to 450 A/m at 976 Hz, 2 to 100 A/m at 3,904 Hz and 1 to 60 A/m at 15,616 Hz. The temperature range is from -192 deg C to 700 (exceptionally 800) deg C. In addition, the anisotropy of magnetic susceptibility (AMS) can be measured at room temperature in variable fields and at variable frequencies. While multidomain magnetite shows no or very low frequency variation of susceptibility, nanoparticle magnetite shows remarkable frequency variation. The field variation of susceptibility is conspicuous in pyrrhotite and titanomagnetite, in the latter correlating with Ti content (indicated by Curie temperatures). The magnetic loss angle is virtually zero in paramagnetic, superparamagnetic minerals and in pure magnetite, being larger in pyrrhotite and very large in basal plane of single crystals of hematite. The orientations of principal susceptibilities are virtually field and frequency independent, while the degree of AMS can be dependent.
DE: 1512 Environmental magnetism
DE: 1518 Magnetic fabrics and anisotropy
DE: 1519 Magnetic mineralogy and petrology
DE: 1540 Rock and mineral magnetism
DE: 1594 Instruments and techniques
SC: Geomagnetism and Paleomagnetism [GP]
MN: Fall Meeting 2005