HR: 1340h
AN: GP13A-0018    [Abstracts]
TI: Can Environmental Magnetism Set Constraints on Rock Magnetic Models? An Example Based on Soils
AU: * Egli, R
EM: eglix007@umn.edu
AF: Institute for Rock Magnetism, 291 Shepherd Laboratories 100 Union Street SE, Minneapolis, MN 55455 United States
AB: Rock magnetic models are needed to understand the occurrence of magnetic minerals in rocks and sediments, and their relationship with geology, biology, and climate. Since the foundation of rock magnetism by Louis Neel, rock magnetic models have been validated mainly on synthetic assemblages of magnetic crystals of known composition, size, and shape. However, the magnetic properties of a natural assemblage of magnetic grains depend as well on a many secondary parameters, such as the occurrence of crystal defects, oxidation gradients, surface effects, and magnetostatic interactions. It is extremely difficult to include these parameters in rock magnetic models, and even if possible, such models have to deal with the unknown statistical distribution of all parameters under consideration. Hence, the exact magnetic properties of natural grain assemblages can be determined only empirically using magnetic unmixing methods. An assemblage of particles with a common geologic and biogeochemical history - hereafter called magnetic component - is characterized by a statistical distribution of physical and chemical properties that depends on the mechanisms of formation and alteration of the particles. The statistical distribution of the parameters related to a specific magnetic component (e.g. pedogenic magnetite, magnetosomes) is expected to show a systematicity that is reflected in the magnetic measurements (magnetic signature). The empirically determined magnetic signature of a natural component is a better reference than synthetic samples for the validation of rock magnetic models. The comparison of the magnetic signature of natural components with current models allows to determine which parameters have to be taken into consideration and which parameters can be neglected. For example: is the Stoner-Wohlfarth model sufficient to model a pedogenic component? Should multiple easy axes and surface effects be taken into account? The case of rock magnetic models applied to low-coercivity pedogenic components is discussed as an example.
DE: 1512 Environmental magnetism
DE: 1540 Rock and mineral magnetism
DE: 1594 Instruments and techniques
SC: Geomagnetism and Paleomagnetism [GP]
MN: Fall Meeting 2005