Constraints on shallow mantle viscosity from morphology and deformation of fast‐spreading ridges

[1] We show that the morphology and the deformation of a fast spreading ridge constrain shallow upper mantle viscosity. A fast spreading center is simulated in a numerical model that couples tectonic deformation due to plate spreading and periodic dike emplacements. The amount of magma intruded into dikes or extruded is enough to make a 7 km thick crust and the axial lithosphere is fixed at ∼2 km thickness. For low viscosities (≤10 Pa·s), the model spreading center is marked by an axial high with relief governed by the axial density structure. For high viscosities (≥10 Pa·s) the axial morphology is a valley and extensional brittle deformation is distributed away from the near‐axis region. The observed morphology and deformation of fast spreading ridges are not consistent with the high mantle viscosity estimated for very dry olivine, as some suggest may result from partial melting related dehydration. Citation: Choi, E., and W. R. Buck (2010), Constraints on shallow mantle viscosity from morphology and deformation of fast‐spreading ridges, Geophys. Res. Lett., 37, L16302, doi:10.1029/2010GL043681.