Water may be a damp squib

Abstract

Experiments on silicon diffusion in the mineral olivine cast doubt on the widely held belief that water has a significant effect on the rheological properties of Earth's upper mantle. See Letter p.213 The long-standing assumption that water has a significant effect on geodynamical processes in the Earth's mantle through influencing the viscosity of quartz and other rocks is brought into question by a new study of silicon diffusion in olivine minerals. Silicon self-diffusion, which is thought to control viscosity in the mantle, was measured in mantle-like conditions of high pressure and temperature as a function of water content. The authors conclude that the effect of water on upper-mantle rheology is small, and that water is unlikely to cause the observed low-viscosity zone. In an accompanying News & Views, John Brodholt considers the implications of this work and the difficulties of matching experimental studies to the extreme conditions found in the mantle.