Elastic thickness of continental lithosphere is modified by both mechanical (thickening and thinning) events and thermal evolution. A simple thermo-mechanical model can account for the processes of tectonic alteration and subsequent thermal reequilibration of lithospheric thermal structure. Mechanical thinning or thickening of the lithosphere directly affects its thickness and flexural rigidity. After a tectonic event, thermal reequilibration proceeds at a rate dependent upon the amount of thinning or thickening and total lithospheric thickness, previous tectonic history, and the heat flux at the base of the lithosphere. Heat flux at the base of the lithosphere is controlled by the efficiency of convective mantle heat delivery. Rapid heat delivery to the base of the lithosphere retards lithospheric thickening, whereas slow conductive heat delivery allows lithospheric thickening at the maximum rate. The relative importance of thermal effects to mechanical alterations of lithospheric elastic thickness depends on the time scale of concern. Very thin lithosphere undergoes rapid thermal evolution such that cooling between tectonic events significantly thickens the lithosphere.

For thick lithosphere, conductive heat transport is so slow that only minor changes in thermal structure and no significant changes in elastic thickness take place between tectonic events. Model results with infinite stretching agree with observations of oceanic lithospheric thickness evolution, showing a divergence from a cooling half-space at about 70 m.y. Model results also agree with independent estimates of continental thermal evolution in the absence of tectonic events. On the longest time scales approaching the age of the Earth, thermal reequilibration is attained, and any tectonic effects are overprinted. The time scale at which the transition between mechanically and thermally dominated elastic thickness evolution occurs depends on the heat transport efficiency of the convecting mantle. For high Nusselt numbers, thermal effects take longer to become important. Even for lower Nusselt numbers, mechanical effects still dominate on time scales of 108 years. Crustal radiogenic heat production reduces the equilibrium lithospheric thermal and elastic thickness. It also introduces a dependence of equilibrium thickness on tectonic crustal thinning or thickening. Model results indicate that on time scales of thrust sheet and sedimentary loading in foreland basins, mechanical effects dominate the evolution of elastic thickness except for very thin lithosphere. The model can be applied to the lithosphere beneath foreland basins so that observed basin geometry can be used to constrain tectonic history prior to loading by thrust sheets and basin sediments. ¿ American Geophysical Union 1993