HR: 0830h
AN: GP11B-0258    [PDF]
TI: Bridging the Gap between Micromag and Cryogenic Magnetometer Measurements
AU: Wetter, L N
EM: lnwetter@ucdavis.edu
AF: Geology Dept., Univ. of California, Davis, Davis, CA 95616 United States
AU: * Verosub, K L
EM: verosub@geology.ucdavis.edu
AF: Geology Dept., Univ. of California, Davis, Davis, CA 95616 United States
AU: Acton, G
EM: acton@geology.ucdavis.edu
AF: Geology Dept., Univ. of California, Davis, Davis, CA 95616 United States
AB: The alternating gradient magnetometer (Micromag) and the cryogenic magnetometer are two of the most useful instruments for determining the mineral magnetic properties of rocks, sediments and soils. However, each instrument has its limitations. Measurements on the Micromag are usually done with small quantities of material whose mass is difficult to determine, especially when sediments and soils are being studied. This makes it difficult to quantitatively relate magnetic parameters determined using the Mircomag with those obtained from conventional measurements on standard-sized samples. On the other hand, standard-sized samples often have isothermal remanent magnetizations (IRMs) that exceed the measurement capabilities of a cryogenic magnetometer. We have developed a method that overcomes the limitations of both instruments. The key to the method is the use of the same small "Micromag" samples for hysteresis and FORC studies done with the Micromag and for IRM acquisition and AF demagnetization studies done with the cryogenic magnetometer. The small sample size keeps the intensities of magnetization below the upper limit for the cryogenic magnetometer. In order to relate these measurements to more conventional magnetic measurements, we measure the anhysteretic remanent magnetization of both the Micromag samples and standard-sized samples prior to the IRM studies. We then determine the mass of the Micromag samples from the mass of the standard-sized samples. The overall approach allows us to bridge the gap between Micromag and cryogenic magnetometer measurements and to report all magnetic properties on a per-unit-mass basis. The method is particularly efficient when used with an automated long-core cryogenic magnetometer operated in a discrete mode.
DE: 1512 Environmental magnetism
DE: 1519 Magnetic mineralogy and petrology
DE: 1521 Paleointensity
DE: 1540 Rock and mineral magnetism
DE: 1594 Instruments and techniques
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2003 Fall Meeting