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Magnetic properties of variably oxidized pillow basalt
Author(s) -
BeskeDiehl S. J.,
Soroka W. L.
Publication year - 1984
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/gl011i003p00217
Subject(s) - remanence , coercivity , pillow lava , basalt , geology , curie temperature , single domain , grain size , saturation (graph theory) , magnetite , materials science , mineralogy , magnetization , ferromagnetism , magnetic domain , condensed matter physics , geochemistry , lava , magnetic field , physics , mathematics , quantum mechanics , volcano , combinatorics , paleontology , geomorphology
In our study of changes in magnetic properties during low temperature oxidation of oceanic pillows, we were able to essentially eliminate variations in grain size which plagued many previous studies. This was accomplished by keeping the cores parallel to the outer glassy margin of the pillow while drilling the variably oxidized portions of the basalt. Curie temperature (T c ) measurements indicated a large range in the degree of low temperature oxidation, although most were in the early stages of maghemitization (T c <300°C). In samples with hysteresis parameters showing pseudo‐single domain behavior, the natural remanent magnetization (J nrm ) and susceptibility both decreased substantially with low temperature oxidation. Thus, the Koenigsberger ratio (J nrm /J induced ) did not change. The reduction in J nrm was mirrored by comparable decreases in saturation magnetization and saturation remanence. Low temperature oxidation also increased the bulk coercivity and the coercivity of remanence in the oxidized basalt relative to the less oxidized. These later results are consistent with the theory that low temperature oxidation generally stabilizes the remanent magnetization of seafloor pillow basalts. The increase in coercivity with oxidation in these pillow basalts contrasts will synthetic samples which show an overall decrease. The behavior of natural samples reflects processes which occur during low temperature oxidation that do not normally occur in synthetic samples, specifically the loss of iron from the grain and perhaps grain cracking.