Open AccessTRM deviations in anisotropic assemblages of multidomain magnetite
Author(s) -
Cogné J. P.
Publication year - 1987
Publication title -
geophysical journal of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.302
H-Index - 168
eISSN - 1365-246X
pISSN - 0016-8009
DOI - 10.1111/j.1365-246x.1987.tb01677.x
Subject(s) - anisotropy , magnetite , condensed matter physics , remanence , magnetic field , magnetization , geology , exponent , magnetic anisotropy , field (mathematics) , geophysics , physics , mathematics , optics , paleontology , linguistics , philosophy , quantum mechanics , pure mathematics
Anisotropic assemblages of multidomain magnetite particles develop an anisotropy of magnetic susceptibility (AMS), which in turn induces deviations of thermo‐remanent magnetization (TRM) from the field direction. From the theories of multidomain TRM acquisition, it is shown that the TRM anisotropy tensor has its eigenvalue ratios ( T i ) related to the principal weak‐field susceptibility ratios ( P i ) by the order of magnitude T i ≃ P 2 i . This relation has been experimentally verified on two sets of highly anisotropic rock samples. The exponent has been determined to be 1.94 in the samples from a Peruvian gabbro, and 1.81 in those from the granite of Flamanville (NW France). Accounting for experimental difficulties in determining the TRM anisotropy tensors, these exponents are judged to agree well with the expected one. It is therefore stressed that AMS measurements provide a good means of evaluating the magnetic field direction from deviated TRM directions, providing magnetic carriers are mainly multidomain magnetites.