Diffusion creep of enstatite at high pressures

Abstract:

Deformation behavior of fine-grained enstatite (g.s. ~ 8 μm) was investigated with triaxial compressive creep experiments at high pressures (4.2 – 6.9 GPa) and high temperatures (1373 – 1573 K) using a deformation-DIA apparatus. Experiments were carried out under anhydrous conditions. In each experiment, a sample column composed of a sample and alumina pistons was assembled with a boron nitride sleeve and graphite resistance heater into a 6.2-mm edge length cubic pressure medium. Experiments were carried out at the National Synchrotron Light Source at Brookhaven National Laboratory. In a run, differential stress and sample displacement were monitored in-situ using synchrotron x-ray diffraction and radiography, respectively. Based on results from this study, the deformation behavior of enstatite under anhydrous conditions has been quantitatively presented in the form of a flow law that describes the dependence of deformation rate on stress, temperature, and pressure. Specifically, data fitting yields the dependence of creep rate on stress with an exponent of n ≈ 1; indicating samples were deformed in the regime of diffusion creep. Experimental results also yield the dependences of creep rate on temperature and pressure with an activation energy of ~250 kJ/mol and activation volume of ~3.5×10^-6 m³/mol, respectively. The flow laws for enstatite, one important constituent component for the upper mantle, quantified from this study provides a necessary constraint for modeling the dynamic activities occurring within Earth’s interior.