How valid are dynamic models of subduction and convection when plate motions are prescribed?

A detailed comparison between fully dynamic and kinematic plate formulation s has been made in models of mantle convection. plate velocity is computed self-consistently from fully dynamic plate models with temperature- and str ess-dependent viscosity and preexisting mobile faults. In fully dynamic mod els, the now is driven solely by internal buoyancy, while in kinematic mode ls the now is driven by a combination of the prescribed surface velocity an d internal buoyancy. Only a temperature-dependent viscosity. close to the e ffective viscosity determined from the fully dynamic models, is used in the kinematic models. The two types of models give very similar temperature st ructures and slab evolutionary histories when the effective viscosity and s urface velocity are nearly identical. In kinematic plate models, the additi onal work introduced by the prescribed velocity boundary condition is appar ently dissipated within the lithosphere: and has little influence on the co nvection under the lithosphere. In models with periodic lateral boundary co nditions, slabs sink into the lower mantle at an oblique angle and this con trasts with the vertical sinking which occurs with reflecting boundary cond itions. Models show that we can simulate Fully dynamic models with kinemati c models under either periodic boundary conditions or reflecting boundary c onditions. (C) 1999 Elsevier Science B.V. All rights reserved.