Thermal fluctuation fields in basalts and the Barbier plot

HR: 1340h
AN: GP53A-0954 [Abstracts]
TI: Thermal fluctuation fields in basalts and the Barbier plot
AU: * Muxworthy, A R
EM: adrian.muxworthy@imperial.ac.uk
AF: Department of Earth Sciences and Engineering, Imperial College London, South Kensington Campus, London, SW7 2AZ, United Kingdom
AU: Heslop, D
EM: dheslop@uni-bremen.de
AF: Fachbereich Geowissenschaften, Universität Bremen, Klagenfurter Straße, Bremen, 28359, Germany
AU: Michalk, D
EM: michalk@gfz-potsdam.de
AF: GeoForschungsZentrum Potsdam, Section 3.3, Telegrafenberg, Potsdam, 14473, Germany
AB: Néel's thermal fluctuation field (H_f) is central to thermoremanent acquisition models, which are key to our understanding of the reliability of palaeomagnetic data, however, H_f is poorly quantified for natural systems. We report H_f determinations for a range of basalts, made by measuring rate-dependent hysteresis. The results for the basalts were found to be generally consistent with the space of the Barbier plot, which is characterized by the empirically derived relationship; log H_f \propto 1.3 log H_C (where H_C is the coercive force), obtained from measurements on a wide range of different magnetic materials. Although the basalts appear to occupy the correct position within the space of the Barbier plot, the relationship within the sample set, log H_f \propto 0.54 log H_C, is different to the Barbier relationship. This difference is attributed to the original Barbier relationship being derived from a wide range of different synthetic magnetic materials, and not for variations within one material type. We consider the relationship between H_C and the activation volume, v_act, i.e., H_C \propto v_act^-0.78 for our sample set. This compares favourably with theoretical predictions, and with previous empirical estimates based on the Barbier plot, i.e., H_C \propto v_act^-0.73.
DE: 1503 Archeomagnetism
DE: 1521 Paleointensity
DE: 1533 Remagnetization
DE: 1540 Rock and mineral magnetism
DE: 1594 Instruments and techniques
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2007 Fall Meeting