The diversity of tectonics from fluid-dynamical modeling of the lithosphere-mantle system

Numerical modeling of the lithosphere has been carried out from many points of view. Most popular and prevalent is the use of the kinematic boundary conditions to move the lithosphere about in the dynamics. We have approached the numerical modeling of the lithosphere-mantle system by treating this as a fluid-dynamical system in which crustal and mantle rheologies and thermal and compositional buoyant forces play dominant roles in delivering the dynamics in a self-consistent manner. We have investigated the development of extensional and compressional tectonic regimes from variations of the crustal density, and compare their temporal evolutions. In comparing with kinematically driven thickening of the lithosphere, we find that the timescales are more self-consistently determined in a full fluid-dynamical treatment than in kinematic models. We emphasize the delicate nature of balancing the chemical buoyancy of the crust with the thermal negative buoyancy of the mantle lithosphere, as the modes and associated timescales of the delamination process are controlled critically by their relative importance. The role of an actively participating buoyant crust cannot by ignored in the overall lithosphere-mantle dynamics. (C) 2000 Elsevier Science B.V. All rights reserved.