Slide 16 of 20

Extension of stable continental lithosphere: Numerical experiments As the lithosphere becomes thinner it also tends to become cooler and therefore stronger (remember a cool rock is stronger than a warm rock). The cooling is related to the thinning the continental crust that concentrates most of the heat-producing elements (Uranium, Thorium, and Potassium). As the radiogenic layer becomes thinner, less heat is produced and the entire lithosphere cools down and become stronger. If extension is faster than the cooling effect (experiment A) then extension localises in a narrow region where a necking instability develops. In contrast if extension is slower than cooling (experiment B) then the strengthening of the lithosphere limits thinning and extension moves into warmer and weaker adjacent regions and extension becomes broadly distributed. Extension rate fast relative to thermal reequilibration. 12cm/y; Extension: 470km; 5Ma. A Extension rate slow relative to thermal reequilibration. 6cm/y; Extension: 340km; 8Ma. B Govers and Wortel, 1995.