Continental tectonics: Selected topics

Cause and effect relations between plate boundary processes and orogeny were investigated using new and refined plate models for the Mesozoic and Cenozoic. Terrane accretion and large components of horizontal shear were shown to be fundamental aspects of orogen evolution. Deep crustal thrust systems, with large lateral transport and vertical stacking of slices of crystalline basement were documented in the Cordillera and Appalachians. New geomechanical models of crystalline thrust sheets and foreland thrust belts emphasized the dominance of tectonic, rather than gravitational stresses. Lithospheric thickening was shown to cause buoyancy forces that control the lateral spread of deformation outward from the interior of an orogen and may modify regional stresses in the vicinity of topographic fronts, resulting in extension within the upper part of the lithosphere coeval with shortening at depth.