Quantitative evaluation of mantle flow traction on overlying tectonic plate: linear versus power-law mantle rheology

SUMMARY Sub-plate mantle flow traction (MFT) has been considered as a major driving force for plate motion; however, the force acting on the overlying plate is difficult to constrain. One of the reasons lies in the variable rheological flow laws of mantle rocks, for example, linear versus power-law rheology, applied in previous studies. Here, systematic numerical models are conducted to evaluate MFT under variable rheological, geometrical and kinematic conditions. The results indicate that MFT with power-law rheology is much lower than that with linear rheology under the same mantle/plate velocity contrast. In addition, existence of a lithospheric root in the overlying plate could enhance MFT, where integrated normal force acting on the walls of lithospheric root is much lower than the shear force in a large-scale domain. In the acting domain of several thousand kilometres, MFT with power-law rheology is comparable to the ridge push of about 3×1012 N m−1, whereas that with linear rheology is comparable to the slab pull of about 3×1013 N m−1. The roles of MFT in driving plate motion are further analysed for the Tethyan evolution. It indicates that MFT with power-law rheology could partially support the Wilson cycles experienced in the Tethyan system, whereas that with linear rheology could easily dominate any kinds of plate tectonic evolutions. The quantitative evaluation of MFT in this study clarifies the roles of rheological flow laws on MFT and could help us to better understand the contrasting results in previous numerical studies.