Magnetic effects of maghemitization of oceanic crust

Journal of Geophysical Research B: Solid Earth
By: , and 

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Abstract

Both theoretical considerations and available experimental results indicate that magnetic effects of maghemitization are strongly dependent on the grain size of the originally unoxidized titanomagnetite. Maghemitization of single‐domain titanomagnetite results in a decrease in coercivity, an increase in susceptibility, and a large decrease in Q ratio. Maghemitization of multidomain titanomagnetite results in an increase in coercivity, a decrease in susceptibility, and no large changes in Q ratio. Single‐domain titanomagnetite is probably resistant to the development of a chemical remanent magnetization (CRM), whereas multidomain titanomagnetite can acquire a CRM during maghemitization. The behavior of pseudo‐single‐domain titanomagnetite, which is the main carrier of remanence in submarine extrusive rocks, is investigated by comparing the magnetic properties of the French‐American Mid‐Ocean Undersea Study (FAMOUS) (less than 0.1 m.y. old) and the Leg 37 (3.5 m.y. old) pillow basalts recovered from the Mid‐Atlantic Ridge near 37°N. Combining electron microprobe analyses, Curie temperature measurements, and cell edge determinations, we find that the FAMOUS rocks are already oxidized (z = 0.38), possibly as a result of some high‐temperature maghemitization during cooling of the magma. Comparison with the more highly oxidized (z = 0.7) Leg 37 pillow basalts indicates that low‐temperature maghemitization of such rocks does not result in appreciable changes of coercivity and susceptibility, although the Q ratio does decrease and CRM seems to be acquired. Such a CRM could account for the anomalously low magnetic inclinations observed at most of the Leg 37 sites.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Magnetic effects of maghemitization of oceanic crust
Series title Journal of Geophysical Research B: Solid Earth
DOI 10.1029/JB086iB05p04009
Volume 86
Issue B5
Year Published 1981
Language English
Publisher AGU
Contributing office(s) Geology, Minerals, Energy, and Geophysics Science Center
Description 12 p.
First page 4009
Last page 4020