HR: 17:15h
AN: GP24A-06    [Abstracts]
TI: Palaeointensities From Hawaiian Surface Lava Flows: a Direct Comparison of Thermal and Microwave Techniques
AU: * Pressling, N
EM: N.Pressling@earth.leeds.ac.uk
AF: University of Leeds, School of Earth and Environment, University of Leeds, Woodhouse Lane, Leeds, LS2 9JT United Kingdom
AU: Laj, C
EM: Carlo.Laj@lsce.cnrs-gif.fr
AF: CNRS, Laboratoire des Sciences du Climat et de l'Environnement, CEA-CNRS, Domaine du CNRS, Bat 12, Avenue de la Terrasse, Gif-sur-Yvette, 91198 France
AU: Kissel, C
EM: Catherine.Kissel@lsce.cnrs-gif.fr
AF: CNRS, Laboratoire des Sciences du Climat et de l'Environnement, CEA-CNRS, Domaine du CNRS, Bat 12, Avenue de la Terrasse, Gif-sur-Yvette, 91198 France
AU: Shaw, J
EM: shaw@liverpool.ac.uk
AF: University of Liverpool, Geomagnetism Laboratory, Department of Earth and Ocean Science, University of Liverpool, Liverpool, L69 7ZE United Kingdom
AU: Gratton, M
EM: gratton@liverpool.ac.uk
AF: University of Liverpool, Geomagnetism Laboratory, Department of Earth and Ocean Science, University of Liverpool, Liverpool, L69 7ZE United Kingdom
AU: Champion, D
EM: dchamp@usgs.gov
AF: USGS, Volcano Hazards Team, US Geological Survey, 345 Middlefield Road, MS-910, Menlo Park, CA 94025 United States
AU: Gubbins, D
EM: gubbins@earth.leeds.ac.uk
AF: University of Leeds, School of Earth and Environment, University of Leeds, Woodhouse Lane, Leeds, LS2 9JT United Kingdom
AB: Palaeomagnetic samples have been collected by the USGS from 16 radiocarbon-dated surface lava flows spanning 0-4.5 kyr on the Big Island, Hawaii. 5 cores from each individual site were assigned to Thellier-Thellier (thermal) palaeointensity analysis; 3 for microwave analysis. The two palaeointensity methods differ in the way energy is transferred to the magnetic system. The microwave method uses high frequency microwaves to directly excite the magnetic minerals and generate spin waves, bypassing the production of phonons. Some energy is still transferred to vibrational energy but the sample matrix is heated to a much lesser extent, the advantage being less chance of thermo-chemical alteration and therefore increased chance of experimental success. Unlike most previous microwave experiments, we have been able to reproduce the characteristic resonant conditions of the cavity at a particular power step and therefore routinely carry out pTRM checks and tail-checks. The Thellier-Thellier experiments had a 61% success rate on a sample level; the microwave experiments had a 35% success rate with less rigorous selection criteria. However, the overall quality of the microwave results is higher with 100% of the microwave samples having a quality factor, q > 5 compared to only 83% of the Thellier-Thellier samples. On a flow level, the mean intensities from the Thellier-Thellier study are generally higher than previously published data: approximately double the present day field. The results from the microwave method are also high with the palaeointensities obtained from the two different methods agreeing to within one standard deviation for 4 of the flows investigated. For the remaining flows, more confidence can be placed in the Thellier-Thellier results due the application of a stricter set of selection criteria and because the flow averages were calculated from more samples. Re-interpretation of individual sample results is also discussed with emphasis on the occurance and treatment of 2-slope Arai diagrams. In addition, the resulting paleointensities from both methods will be presented within the context of augmenting the secular variation record over a period when geomagnetic secular variation has been low in the Pacific region.
DE: 1500 GEOMAGNETISM AND PALEOMAGNETISM
DE: 1521 Paleointensity
DE: 1522 Paleomagnetic secular variation
DE: 1594 Instruments and techniques
SC: Geomagnetism and Paleomagnetism [GP]
MN: Fall Meeting 2005