Rheology of fine-grained forsterite aggregate under deep upper mantle conditions

Abstract

In order to clarify the dominant deformation mechanism in the upper mantle, we have conducted deformation experiments at pressure and temperature conditions of 3.0–5.3 GPa and 1473–1573 K, respectively, using fine-grained (grain size of ∼1 um) forsterite aggregate. The analysis of stress-strain rate data taken at dry conditions using a flow law equation yielded the activation volumes of ∼7 and ∼11 cm3/mol for diffusion creep and dislocation creep accommodated grain-boundary sliding, respectively. The present results implies that the diffusion creep is the predominant deformation mechanism at the most conditions of pressure, temperature and strain-rate in the upper mantle.