Silicon diffusion in forsterite aggregates: Implications for diffusion accommodated creep

Silicon diffusion rates were determined in fine‐grained (∼4.5 µm) hot‐pressed forsterite aggregates at 900° to 1200°C and 0.1 MPa using a 30Si‐tracer and standard SIMS analysis. There is no measurable difference in diffusion rates between samples buffered by excess MgO or SiO2, nor samples run in dry N2 or H2/CO2. The results yield the Arrhenius parameters D0, bulk = 5.4 × 10−9 m²/sec and Q = 203±36 kJ/mol. At 1200°C, the grain boundary diffusion rate of 30Si is similar to 26Mg (Si ∼10 times greater), ∼10² less than Fe, and ∼105 less than O. In addition, the 30Si grain boundary diffusion rate is ∼109 greater than the Si volume diffusion rate and indicates that diffusional transport of Si in forsterite aggregates is dominated by grain boundaries.