Fig. 9: The evolution of principal axes of deviatoric stresses for the upper crust and effective viscosity within the lithosphere in southwestern North America.

a–f Variation of the principal axes of horizontal deviatoric stresses for the upper crust at 35.9, 30, 24, 18, 12, and 6 Ma, respectively. Black arrows represent compressional and red arrows represent tensional stresses. The color-coded circles and vectors represent the stretching direction of metamorphic core complexes shown in yellow and Miocene faults and dykes trend shown in green and blue. g–l Depth averaged effective viscosity of the North American lithosphere, from surface to the base of the lithosphere, at 33, 28, 20, 14, 8, and 3 Ma, respectively. The map images were created by authors using: www.soest.hawaii.edu/gmt/ and www.paraview.org/.