Cooling of the Oceanic Lithosphere
As we have already noted, the solution developed in Section 4–15 is also relevant to the cooling of the oceanic lithosphere adjacent to a mid-ocean ridge. In Chapter 1 we discussed how the mid-ocean ridge system is associated with ascending mantle convection. The surface plates on either side of the ridge move horizontally with a velocity u, as illustrated in Figure 4–22. The plates are created from the hot mantle rock that is flowing upward beneath the ridge. This rock is cooled by the seawater and forms the rigid plates that move away from the ridge. Since the oceanic lithosphere is thesurface plate that moves rigidly over the deeper mantle, it can be identified with the part of the upper mantle whose temperature is less than some value below which mantle rocks do not readily deform over geologic time.
