CSEDI Collaborative Research: Grand Challenge for Experimental Study of Plastic Deformation Under Deep Earth Conditions

Yale University, New Haven CT

Investigators

Abstract

The goal of this research program is to develop and utilize experimental capabilities for studying the plastic properties of rocks at conditions of the deep Earth. Over geologic time we see that continents have been ripped apart with plate boundaries punctuated by earthquakes and volcanoes. However, over the vast regions of the Earth, these processes proceed smoothly and slowly. While earthquakes express the dynamic character of Earth deformation, the slow movement of the continents provides the driving force. The enabling process for this large-scale motion is the plastic deformation of rocks throughout the Earth's mantle. The foundation of plate tectonics rests on the contention that rocks deform slowly but surely at the high pressure and temperature of the deep Earth. This research program is to continue to build experimental capabilities to quantify the plastic character of rocks as a function of depth in the Earth. This program works at the juncture of high-pressure apparatus development and national synchrotron facilities that can provide intense x-ray probes. This union promises experimental capabilities that increase the depth range of the Earth that we can access, with high precision measurement, by a factor of 100 from previous studies. The data that will come from this program will enable testing and modifying of models of Earth evolution. These deformation facilities enable new directions in Earth material research at mantle pressure and temperature including elastic wave attenuation at seismic frequencies, reaction kinetics, thermal diffusivity, and relationship of lattice preferred orientation to deformation geometry, which links seismic anisotropy to flow history. They also provide a potential facility and technical knowhow for studying material strength and plasticity at extreme conditions such as those generated in the next generation power plants. Stress, strain, pressure, and temperature are the primary variables that need to be measured during a deformation experiment. With the aid of the national synchrotrons (the Advanced Photon Source and the National Synchrotron Light Source), the investigators have developed the tools to make these measurements. They have also built the first generation of high-pressure apparatus for introducing 'large - volume high pressure' technology into deformation machines. They are now able to make accurate rheology experiments at pressures 1 to 2 orders of magnitude higher than could be achieved 10 years ago. The next phase is to take full advantage of the current hydrostatic high-pressure equipment, including advanced technologies for making polycrystalline diamonds, to reach lower mantle conditions. The goals of this program are to 1) increase the pressure range for deformation experiments to 30 - 40 GPa, well into the lower mantle, 2) improve measurement resolution of stress and strain with a combination of hardware and software developments, 3) enable simultaneous measurements of a sample properties such as preferred orientation of grains and acoustic velocity, 4) explore advanced techniques such as those developed by the synchrotron community but may be useful to earth science goals. These are often high risk, but high return tools such as white beam Laue diffraction that could yield very detailed information about the individual grains within a polycrystal.