Viscoplastic Rheology of α-Quartz Investigated by Nanoindentation

Quartz is an abundant mineral in Earth's crust whose mechanical behavior plays a significant role in the deformation of the continental lithosphere. However, the viscoplastic rheology of quartz is difficult to measure experimentally at low temperatures without high confining pressures due to the tendency of quartz (and other geologic materials) to fracture under these conditions. Instrumented nanoindentation experiments inhibit cracking even at ambient conditions, by imposing locally high mean stress, allowing for the measurement of the viscoplastic rheology of hard materials over a wide range of temperatures. Here we measure the indentation hardness of four synthetic quartz specimens and one natural quartz specimen with varying water contents over a temperature range of 23 degrees C to 500 degrees C. Yield stress, which is calculated from hardness but is model dependent, is fit to a constitutive flow law for low-temperature plasticity to estimate the athermal Peierls stress of quartz. Below 500 degrees C, the yield stresses presented here are lower than those obtained by extrapolating a flow law constrained by experiments at higher temperatures irrespective of the applied model. Indentation hardness and yield stress depend weakly on crystallographic orientation but show no dependence on water content.

Automated summary

Quartz, an abundant mineral in Earth's crust, is difficult to measure viscoplastic rheology at low temperatures, but instrumented nanoindentation experiments allow for measurement over a wide temperature range. The study found that indentation hardness and yield stress of quartz are not affected by water content and only weakly depend on crystallographic orientation.