Whole-Mantle Convection
Mantle geotherms are given for whole-mantle convection “(Curve a) and layered mantle convection” (Curve b). The range of val- ues for the mantle solidus and the minimum temperatures in a subducted slab are also given. stood as the one beneath the oceans. One way to model the temperature distribution in the continental lithosphere would be to apply the same one dimensional half-space cooling solution that we applied earlier to the oceanic lithosphere. However, as shown in Figure 4–28, the predicted mantle heat flows are considerably lower than the observed values. Also, if old continental lithosphere continued to cool, it would also continue to subside according to Equation (4–209) (see Problem 4–56). The result would be continental cratons overlain by a continuously thickening sedimentary cover. This condition has not been observed, so there must be a heat input into the base of the old continental lithosphere that retards further cooling and allows old continental lithosphere to tend toward a steady-state temperature profile.
The input of heat to the base of the lithosphere is attributed either to mantle plumes impinging on the base of the lithosphere or to secondary convection in the lower lithosphere or to both, as discussed.
