Research | Rock and Mineral Physics Laboratory

Rheological behavior of rocks and minerals

Our primary research target is elucidating the small-scale physics that control the rheological behavior of geological materials. We conduct deformation experiments to determine how the motion and evolution of crystal defects, such as dislocations, influence macroscopic behavior. We work at a range of conditions to examine plasticity and viscoelasticity in materials characteristic of Earth's upper mantle and crust. These experiments include uniaxial compression; triaxial defomation compression, extension, and torsion; and micromechanical testing including nanoindentation and micropillar compression. You can find an overview lecture of some of these topics from 2019 here.

Dynamics of polymineralic systems

Rocks in Earth's interior are inherently composed of multiple mineral phases. However, we have the best understanding of the rheological behavior of rocks composed of single minerals (e.g., dunites or quartzites). The addition of secondary phases raises the possibility of several additional effects that may be critical to the behavior of the solid earth. For example, secondary phases modify grain-size evolution and therefore may promote grain-size sensitive deformation mechanisms. In addition, the presence of secondary phases introduces phase boundaries (as opposed to grain boundaries between crystals of the same phase), which may dramatically alter the macroscopic behavior. Key targets for investigation include the evolution of the spatial distribution of secondary phases (phase mixing) and the influence of phase boundaries on mechanical properties.

Texture development and anisotropy

The deformation of crystalline materials at high temperatures often leads to the formation of crystallographic textures, in which individual crystals rotate into preferred orientations. Because individual crystals exhibit anisotropy in their physical properties, textured materials also exhibit some anisotropy. Physical properties that can be anisotropic include elasticity (and therefore seismic properties), viscoplasticity, and electrical conductivity. We conduct experiments to investigate both texture formation and the magnitude of anisotropic properties of textured rocks. The results of these experiments are used to calibrate models of texture formation to predict anisotropy in geodynamic simulations and to interpret textures preserved in rocks now exposed at Earth's surface.

The dynamics of partially molten rocks

Partially molten rock (melt fraction < 0.2), mush (melt fraction from 0.3 to 0.5) and magma (melt fraction > 0.5) are found throughout Earth’s mantle, asthenosphere and crust. The seismic, conductive, and transport properties of these materials are significantly influenced by melt fraction and melt distribution, both of which can change during deformation and as a result of chemical reactions. We conduct experiments to determine the rheological properties and microstructural evolution of partially molten rocks and mushes as a result of deformation, reactive flow, and exposure to pore-pressure gradients. Experimental results are also used to identify the processes and conditions that facilitate melt migration and the formation of melt-rich features. Specific applications of our work include chemical exchange between Earth’s crust, mantle, and atmosphere; mantle flow and melt extraction on Jupiter’s moon Io; and magma ascent in volcanic plumbing systems.

The nature of grain boundaries in rocks

The properties of the interfaces between adjacent crystals, grain boundaries, strongly influence many physical properties. These properties include the viscosity, seismic attenuation, and electrical conductivity of rocks. We investigate the structure and properties of grain boundaries to quantify that influence and build constitutive models rooted in the microphysics of crystalline solids. We investigate the properties of grain boundaries with mechanical tests (uniaxial compression, micropillar compression, nanoindentation) and with microscopy (transmission electron microscopy, electron-backscatter diffraction).