Slide 39* of 40

Ridge-Push Stress Acting on a Continental Lithosphere The aim of this exercise is to estimate the strain rate at which a continental lithosphere in isotatic equilibrium with a MOR, as defined in Slide 6a, would deform under the MOR's ridge-push. The thickness of the crust is zc=35km. The thickness of the entire continental lithosphere is zl=140km. The density of the crust is constant with depth ρc=2700kg.m-3. The density of the lithospheric and asthenospheric mantle at 0ºC are 3380 and 3395kg.m-3 respectively. The coefficient of thermal expansion is α=3.10-5. The continental geotherm is a two-stage linear geotherm with: T=0ºC at z=0, T=600ºC at z=zc and T=1330ºC at z=zl. The temperature in the asthenosphere is constant at 1330ºC. 1/ Using the MOR defined in Slide 6a, determine the surface elevation (h) of the continental lithosphere Using the MOR defined in Slide 6a. To make things easier the pressure at zl+h underneath the MOR is 4.31 109 Nm-1. 2/ Determine the Gravitational Potential Energy of the continental lithosphere. 3/ Determine the Gravitational Force acting in between the MOR and the continental lithosphere. The GPE of the MOR down to zl+h is: 2.92 1014Nm-1. 4/ Using the rheological parameters given in Slide36, and a l (the ratio between pore pressure and lithostatic pressure) of 0.36, construct the rheological profiles for the following strain rate: 10-14 s-1, 10-15 s-1, 10-16 s-1, 10-17 s-1. 5/ Estimate the integrated strength of the continental lithosphere at each strain rates. 6/ Estimate the strain rate at which the continental lithosphere would deform under the ridge-push.