. The Earth beneath the sea : History . I 5 25 125 ;^ DISTRIBUTION OF APPARENT SUSCEPTIBILITIES Fig. 10. The distribution of apparent susceptibilities of (a) basalts dredged from the Mendocino escarpment and (b) basaltic lavas from Mull. (From R. G. Mason, un- published.) less than 575°C. Since temperatures within the earth increase with depth, there will exist everywhere a surface of magnetic discontinuity corresponding to the Curie point isotherm. There is some uncertainty as to the depth at which the Curie point might be reached; on the basis of present information it seems r
. The Earth beneath the sea : History . I 5 25 125 ;^ DISTRIBUTION OF APPARENT SUSCEPTIBILITIES Fig. 10. The distribution of apparent susceptibilities of (a) basalts dredged from the Mendocino escarpment and (b) basaltic lavas from Mull. (From R. G. Mason, un- published.) less than 575°C. Since temperatures within the earth increase with depth, there will exist everywhere a surface of magnetic discontinuity corresponding to the Curie point isotherm. There is some uncertainty as to the depth at which the Curie point might be reached; on the basis of present information it seems reasonable to assume that it will be between 20 and 50 km below the sea floor, and, therefore, well below the base of the oceanic crust. Lateral variations in its de]jth will lead to anomalies in the magnetic field, which, therefore, provide a means for studying the thermal state of the upper mantle. 6. The Magnetic Surveys of the North-east Pacific Much of the magnetic data obtained at sea is in the form of long unrelated profiles recorded during passage of a ship. These are of limited usefulness
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