The magnetic properties of igneous rocks from the ocean floor

• Published in: Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences
• Format: Article in Journal/Newspaper
• Language: English
• Published: The Royal Society 1971
• Subjects: Pacific; Scotia Sea
• Online Access: http://dx.doi.org/10.1098/rsta.1971.0011; https://royalsocietypublishing.org/doi/pdf/10.1098/rsta.1971.0011

The measured magnetic properties of submarine igneous rocks, comprising data from approximately 300 specimens, are summarized. Basaltic rocks dominate the collection numerically, and are distinguished by their high Q (ratio of remanent to induced magnetic intensities). Limited numbers of altered samples indicate that spilitization, chloritization, and serpentinization can drastically reduce the intensity of magnetization. The available thermomagnetic data suggest that low Curie points may be typical of quenched basalts. The limited range of submarine igneous rock types examined, and the strong bias towards quenched samples necessitates a supplement to this summary in the form of a discussion of studies of magnetic properties from selected igneous rocks outcropping above sea level. In these studies, serpentinization of ultrabasic rocks has been observed in one case to increase the intensity of magnetization; chloritization and spilitization are confirmed as being magnetically destructive; maghaemitization may have destructive effects; titanomagnetite oxidation variation dominates in magnetic change of basaltic lavas (and some corresponding chemical changes are likely to occur); basaltic intrusives have a much more limited titanomagnetic oxidation range than is generally observed in lavas; and spontaneous demagnetization with time probably exists, at least in basalts. New data are presented. These include the magnetic properties of harzburgites dredged from the Macquarie Ridge, and eight pillow basalts from the South Pacific and Scotia Sea. The former suggest that harzburgite is capable of creating strong magnetic anomalies. Samples for the latter study were sufficiently large for study of the variation of magnetic and petrological properties with depth beneath the cooling surface. Systematic texturual changes from glassy exterior, through a variolitic zone to aphanitic interior characterize the silicates in most samples. Chloritization is present in some aphanitic parts. Serpentinization is present in some ...