Regional viscosity variations, small‐scale convection and slope of the depth‐age1/2 curve

Abstract

Cooling plate and cooling half‐space models are commonly employed to describe the depth‐age1/2 curve of seafloor. These conductive models are not able to reproduce the large range of subsidence rates that are observed with reasonable changes in the physical parameters. We examine the influence of small‐scale convection in the mantle on subsidence rates with a one‐dimensional, parameterized‐convection model. The parameterization is based on a recent experimental study of thermal convection in a fluid with temperature‐dependent viscosity. In our model, convection in the asthenosphere begins at the ridge axis, enhancing heat transfer out of the asthenosphere and increasing the subsidence rate above that for simple conductive cooling. Variations in deformation mechanism, temperature and water content of the mantle cause changes in viscosity that affect the vigor of convection and may be responsible for large variations in subsidence rates. Average subsidence rates can range from ∼250–500 m/Ma1/2 when small‐scale convection is considered.