Low-temperature olivine rheology at high pressure

Abstract

San-Carlos olivine rheology was investigated at pressure ( P) up to 9 GPa and temperature ( T) lower than 890 °C. Six powder specimens were cold compressed and sintered into dense and compact materials, then deformed during relaxation experiments carried out at constant pressure and temperature in DIA-type cubic-anvil apparatus. Sample elastic strain was monitored during relaxation by in situ X-ray diffraction. Run product microstructures were characterized by transmission electron microscopy (TEM). A new method for measuring olivine rheology at high pressure from X-ray diffraction peak broadening is documented. From the data collected between 500 and 740 °C, the following rheological law is obtained: ε ̇ (s −1)=2.6 +23 −2.3 ×10 16 × exp − (564±89)×10 3 RT( J/ mol) 1− σ( GPa) 15.4±1.0 2/3 2 , where ε ̇ and σ are respectively the olivine microscopic plastic strain rate and internal stress, and R is the gas constant. TEM investigation of deformed sample microstructures reveals that this law corresponds to the activation of c-dislocation glide, and is thus representative of the olivine low-temperature dislocation-creep regime at high pressure.