Rheological profile of the continental lithosphere
The figure on the right illustrates the dependence of the rheology of the continental lithosphere on temperature. From left to right the temperature at the Moho increases from 400ºC up to 700ºC. The strength of the lithosphere, in both compression and extension (the surface area of the dark and pale blue regions respectively), has been averaged over the lithospheric thickness assuming for the mantle either a power law creep or a combination of power law and Dorn law. One can see that as temperature increases, the averaged strength of the lithosphere decreases significantly.
The integrated strength of the continental lithosphere (in Nm-1) is simply defined by the vertical integration (integration over depth) of the rheological profile. Since the frictional sliding depends on the tectonics regime, three "strengths" can be defined for compressional (Fedt), transcurrent (Feds), and extensional (Fedc) tectonic regime:
The figure on the right shows the integrated strength of the lithosphere as a function of temperature at the Moho. At a temperature of about 500ºC the upper mantle is the stronger layer of the lithosphere (in blue in the inset). Because the power law creep is exponentially dependent on the temperature, a relatively small increase in temperature will significantly reduce the integrated strength of the lithosphere. Indeed when temperature at the Moho is close to 700ºC the strength of the upper mantle drastically decrease. Past 700ºC, the stronger layer of the lithosphere is the brittle upper crust the rheology of which has no dependence on temperature. The red and the blue curves are the integrated strength in extension and compression respectively.