Grain‐Boundary Diffusion Creep of Olivine: 1. Experiments at 1 atm

Abstract

Abstract We conducted one‐atmosphere uniaxial compression experiments on fine‐grained (~1 μm) Fe‐bearing olivine (Mg 1.8 Fe 0.2 SiO 4 ) aggregates that were variably doped with CaO ± Al 2 O 3 . We identified power‐law interface‐controlled creep at low stresses and grain‐boundary diffusion creep at high stresses, which operate as mutually coupled, that is, sequential processes. We established constitutive equations for interface‐controlled creep and diffusion creep of undoped olivine and used the combined rate equation as a reference to examine the effect of doping on creep rates. Ca and Al were found to enhance rates of both interface‐controlled creep and diffusion creep above certain temperatures, and this effect becomes significant with increasing temperature. We attribute the rate enhancements to grain‐boundary disordering promoted by grain‐boundary segregation of the dopants at near‐solidus conditions. The enhancements are well described in relation to the sample solidus temperature and an additional activation energy relative to that of the reference creep state.