Acquisition of a Rock Deformation Apparatus to Study Rheology and Microstructure

Washington University, Saint Louis MO

Investigators

Abstract

This project will support the acquisition of a new apparatus to study the properties of viscously deforming rocks at high pressure and temperature. The viscous flow of rocks is an essential aspect of the growth of mountains, the convection of the mantle, and the motion of tectonic plates. Moreover, the deformation of rocks is elemental to numerous geologic hazards, such as earthquakes, tsunami, and volcanic eruptions. By studying rock rheology in controlled laboratory setting we can develop new insight into the materials science of rocks, and provide tools for numerous geological or geophysical investigations. Unlike many other disciplines, the primary instrumentation used in rock deformation laboratories cannot be purchased commercially, but must be built to specification. Nearly every apparatus used in a rock deformation lab has special capabilities that enable specific types of investigations. The apparatus that will be built for this project is particularly useful for the study of rocks that experience extremely large magnitudes of deformation, such as those that might be sheared along the boundaries between tectonic plates. The objective of this project is to construct a second Large Volume Torsion (LVT) apparatus, building upon an existing successful design. The LVT has several key characteristics that render it unique among rock deformation apparatuses. It is able to generate high pressures and temperatures, as well as large shear strains, on samples that are large enough to provide statistically meaningful information about deformation microstructures. Pressure, up to several GPA, is generated using tapered Drickamer-style anvils and a solid ceramic confining medium. Resistance heaters generate temperatures up to 1600 K. Large shear strains (> 10) can be generated by rotating one anvil with respect to the other. There are a number of projects underway that use data from the LVT apparatus, as well as several targets for future efforts. Experiments on the deformation and mixing of two-phase composites are used to understand the origins of mylonites and the rheology of plate boundary shear zones. Experiments on grain-size evolution over a large range of shear strains help clarify strain-weakening processes. Experiments to investigate the development of crystallographic preferred orientation are used to better interpret seismic anisotropy in the mantle. Experiments at low strain-rates will be used to elucidate the rate dependence of microstructural evolution. The acquisition of a second apparatus will effectively double the capacity of the rock deformation lab at Washington University in St. Louis, allowing the PIs to train more students, host visitors, develop new techniques, and explore new parameter space. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.