My colleague from Boston has carried out a successful defomation experiment this week. The result is shown in the figure below. The deformation occurred at 1300C and 300 MPa confining argon pressure on titanium and calcium bearing synthetic olivine (fine-grained). Compressive differential stress (upwards force) was up to 315 MPa / 33 kN in the dislocation creep field. The transition to this form of power law creep deformation occurs at around 200 MPa and higher depending on the type of olivine material that is deformed. At lower stresses diffusion creep is dominant. In the figure you can see a typical barrel shaped specimen that was originally longer and a straight cylinder in shape. The higher compression direction compared to the uniform confining pressure comes from the sides. The specimen will be sectioned and imaged to determine the microstructure using the scanning electron microscope (SEM). The remainer will be precision ground to 10 mm in diameter and put back in the apparatus for another deformation experiment.
The most important result from the experiment will be a new flow law that predicts how this type of material deforms under high temperature and pressure comparable to upper mantle conditions in the Earth (100-400 km deep). However, whether the data trend can be extrapolated to geological time scales and coarser grain size remains debatable.
Fig. 1 Deformed fine-grained olivine (original length 20.8 mm) sandwiched between two alumina loading pistons.