Fig. 4: Within zones of high gravitational body forces, the relaxation of the crustal root generates a “rolling hinge” mode within the middle and lower crust.
From: The role of gravitational body forces in the development of metamorphic core complexes
a–d Zoom-in of boxed region in Fig. 3, illustrating strain concentration and the rotation of principal axes of deviatoric stresses within the upper crust through high- and low-angle normal faulting under the influence of basal tractions, free slip side boundaries, and non-uniform distribution of gravitational body forces. Red vectors represent tensional and black vectors represent compressional principal axes of deviatoric stresses. Black arrows show sense of slip offset accumulation on the detachment. Finite strain (values represent second invariant of strain tensor) develops in response to extension and fault rotation. The blue lines denote where main and conjugate detachments, respectively, remain active. Note that in the experiment with a crustal root, a reduction in crustal thickness in response to isostatic rebound of the crustal root and collapse of topography increases the local strains within a necking zone which accommodates the doming and exhumation of the middle crust at the surface, with the numbers showing their dip angles in degrees. Note the decrease of dip angle from 38° to 20° to 8° of the asymmetric shear zone, showing the rolling hinge mode for metamorphic core complex formation. Red areas on the top panels represent locations affected by both erosion and sediment accumulation. Experiments start at 36 Ma and evolve to 0 Ma. Stages of evolution are given in Ma. MCC metamorphic core complex.
