Message #258117

[Lisa Wolfe]

Fig. 4. Idealized snapshots of one side of a mid-ocean ridge, to show the development of oceanic magnetic stripes, from the mid-Cretaceous period of Mesozoic time to the Present, as a result of gradual narrowing of the active mid-ocean volcanic zone. A is the ridge axis. This diagram, modified from Keith, Fig. 10, shows migration of the blocking temperature isotherm B. The reddish color to the right of B indicates the portion of the ridge for which the principal magnetic source remains above the blocking temperature. [The geomagnetic polarity (normal or reverse) and the geologic time scale are from D. Kent and F. Gradstein,1986, “Jurassic to Recent chronology,” in The Western North Atlantic Region. Geol. Soc. America, Geology of North America, v. M, pp. 45-50, Plate 1.]