Mountain building and exhumation processes through time: inferences from nature and models

Orogenic belts involving initially hot lithospheres, as exemplified by accretionary-type orogens, commonly show distributed deformation and retrograde PT paths with a concomitant decrease in pressure and temperature. Paths may track geotherms, indicating thermal equilibrium, consistent with slow strain and exhumation rates, limited strain localization, and consequently limited topographical gradients and distributed erosion. Such patterns are more common in Precambrian times than in younger periods of the Earth history. In contrast, orogens involving initially stiff lithospheres show exhumation PT paths that track isothermal decompression reflecting high strain rates along major shear zones, a feature typical of Phanerozoic collision belts. Field evidence, analogue and numerical models emphasize that strain localization has first-order consequences for the tectonic evolution of orogenic zones including structure, metamorphism, exhumation processes, topography, erosion and sedimentation modes.