Comparison of paleostress magnitudes from calcite twins with contemporary stress magnitudes and frictional sliding criteria in the continental crust: Mechanical implications

The evolution with depth of paleo-differential stress magnitudes (mostly derived from calcite twinning paleopiezometry) in various tectonic settings is compared to the modern differential stress/depth gradients deduced from in situ measurements. Despite dispersion, both independent sets of stress data support to a first-order that the strength of the continental crust down to the brittle-ductile transition is generally controlled by frictional sliding on well-oriented pre-existing faults with frictional coefficients of 0.6–0.9 under hydrostatic fluid pressure. Some ductile mechanisms may, however, relieve stress and keep stress level beyond the frictional yield, as for instance in the detached cover of forelands. The main conclusion is that despite inherent differences, contemporary stress and paleostress data can be combined to bring useful information on the strength and mechanical behaviour of the upper continental crust over times scales of several tens of Ma.