Thermoelastic bending of the lithosphere: implications for basin subsidence

Abstract

Summary. Thermoelastic stresses are capable of producing significant lithospheric deflection. A systematic approach to modelling this effect is presented, in which the lithosphere is presumed to behave as a thin, elastic (or viscoelastic) plate on a fluid substrate, and lateral variations in basal heat flow induce both vertical buoyant loads and thermoelastic bending moments. The amount of uplift or subsidence produced by a given heat source depends on a number of factors, including the strength, duration and lateral extent of the thermal anomaly, and the thickness, density, rigidity and viscosity of the plate. The mechanical response of the plate is characterized by two distinct length scales (one for shearing, the other for bending) and the deformation produced depends critically on the scaled width of the heat source. The plate acts as a low pass spatial filter in response to thermal loads, but has a narrow band pass filter response to applied moments. The temporal response to an abrupt change in basal temperature or heat flow also depends on the ratio of the thermal diffusion time for the plate versus the viscoelastic relaxation time of the material. A rapid, localized increase in basal heat flow will initially produce a central depression and a peripheral uplift. Thus, while it is often assumed that the main depositional phase in platform basins is associated with the cooling and contraction of the lithosphere following an earlier thermal doming event, it is shown that, if conditions are right, a basin may also form in direct response to the initial heating event. Either way, subsequent thermal equilibration and viscous stress relaxation will tend to modify the initial deflection profile.