Deformation and metamorphism in convergent orogens: a model for uplift and exhumation of metamorphic terrains

Summary A conceptual model is presented for deformation, uplift and exhumation in convergent orogens based on flexural models of foreland basin subsidence, the role of inherited rifted margins in convergent orogens, critical wedge theory and the use of P-T-t data to construct particle paths within the deforming orogen. Three states of overthrust orogens can be defined, based on the relative rates of mass loss by erosion and mass addition by accretion and underplating. Rapid exhumation of metamorphic terrains is most likely in the steady state, where erosion balances accretion; a constructive state, where mass addition outweighs erosion, initially results in deep burial and relatively little exhumation; a destructive state, where mass loss outweighs mass addition, results in slow exhumation or subsidence of metamorphic rocks, depending on whether mass is lost by erosion or redistributed during extension. In order to test these predictions, reliable P-T-t data are required on peak metamorphism, pluton emplacement, cooling, exhumation, and uplift, for a range of localities within an orogen.