Figure 2

Viscosity and density structure. First row shows lithology (a), viscosity (b) and density structure (c) 1 Myr prior to the onset of extension. Colors and labels for (a) are as in Fig. 1a. Black lines in (b) and (c) show profiles of minimum and maximum values of viscosity and density and viscosity, respectively, as a function of depth. Viscosity is calculated as half the ratio of a second invariant of the deviatoric stress tensor, \(\sigma {^{\prime} }_{II}=\sqrt{\sigma {^{\prime} }_{kk}}\), to a second invariant of the deviatoric strain rate tensor, \(\dot{{\epsilon }}{^{\prime} }_{II}=\sqrt{\,\dot{{\epsilon }}{^{\prime} }_{kk}}\). (d–f) show the same properties for 9 Myr after the onset of extension. (g–i) show the same properties for 15 Myr after the onset of extension.