Magnetic properties of low-petrologic grade non-carbonaceous chondrites

概要

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The magnetic properties and paleointensities of a number of non-carbonaceous chondrites show a considerable variation. Enstatite chondrites are far more magnetic than others and record ancient fields of 7 to 16 Oe. Abee has a high field, recorded in individual clasts and the random directions suggest the magnetization was pre-accretional. Indarch and Yamato-691 also record high fields, but have a single direction of magnetization, so we cannot infer if the magnetic record is of pre- or post-accretional origin. A series of L and LL chondrites (Bjurbole, Yamato-74191,Mezo Madaras and Chainpur) contain plessite and it is therefore only possible to infer early magnetic fields at temperatures below 550℃, the transition temperature for plessite. Nevertheless, they have random components of magnetization and it is possible therefore that they record pre-accretional remanence. If these samples were reheated as suggested by others, we cannot explain the random directions, unless it is in some way related to tetrataenite, which is highly anisotropic. Ancient fields recorded in these samples are in the range of .1-.7 Oe. Finally, ALHA77304 has no plessite, is an LL chondrite and records two components. The stable component may be of primary origin and if so records a field of 0.45 Oe.
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