A Thermal Constraint on the Duration of Folding with Reference to Acadian Geology, New England (USA)

Folding of isograd surfaces during metamorphism must occur with sufficient rapidity that thermal equilibrium is not first reached between the limbs of a fold. A maximum estimate of the duration of folding obtained by solving the heat equation is proportional to the square of the wavelength of the fold and inversely proportional to thermal diffusivity. The thermal maximum is reached late in folding in the cooler regions of a fold and early in folding in the hotter regions. Application of a simple analytical model indicates that Acadian folding in eastern Vermont, western New Hampshire, and central Massachusetts occurred in less than 1 m.y. at plate tectonic velocities, if geological studies which indicate that isograds were folded while hot are correct.