Ilmenite lamellae and stability of magnetization

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I have analyzed magnetic data from four deep‐sea basalts which have undergone the “exsolution” stage of high‐temperature oxidation, but have not begun the “replacement” stage. Even when ilmenite lamellae development was extensive, coercivities were low with a coercive force (Hc) of 11.7 mT (1 mT=10 Oe) and medium destructive field (MDF) of 9.1 mT. The remanence vector exhibited a directional swing of 30° upon alternating field (AF) demagnetization. Thus, few of the titanomagnetite intergrowths behaved like single‐domain grains. This tentative conclusion is supported by those previous studies of subaerial basalts and synthetic materials which optically identified the degree of oxidation and in which no titanomagnetite granulation was observed. In these studies, MDF's generally did not increase above 15 mT during ilmenite lamellae formation. Those natural and synthetic samples which exhibit features of the “replacement” stage have large natural remanent magnetization (NRM) intensities and high coercivities suggesting that despite intense hematization, single‐domain magnetite may still be present. Copyright 1988 by the American Geophysical Union.

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Geophysical Research Letters