CAREER: Measuring the tectonic and volcanic stresses* preserved in crystals

Baylor University, Waco TX

Investigators

Abstract

Earthquakes and volcanic eruptions are produced by the imbalance of geologic forces. Direct measurements of the responsible stresses are impossible because the processes are dangerous to approach or occur deep underground. Minerals are passive passengers within these dynamic environments, who then become valuable recorders of stress as they are deformed. Emergent synchrotron X-ray microdiffraction and Raman spectroscopy technologies now make it possible to quantify geologic stresses by carefully measuring changes in the atomic structure of minerals. For this CAREER award, the investigator and his team will perform fundamental research to fully explore and validate mineral and crystal deformation studies. The research program will dovetail with a 3-tiered education program that relies upon the intrinsic beauty of gemstones to capture the minds and imagination of its audience. The PI will introduce an interactive mineral display to the local museum, implement a Gems course for non-major undergraduates, and develop of a geovisualization lab for diverse graduate student research. Minerals provide an in-situ record of dynamic geologic processes because their growth and deformation respond to the surrounding environment. Synchrotron X-ray microdiffraction and Raman spectroscopy are new tools for quantifying how minerals are deformed. Synchrotron microdiffraction works by using X-ray diffraction patterns to structurally characterize minerals with micron spatial resolution. Raman spectroscopy is similarly high resolution, but instead measures strain by exploiting a mineral’s elastic response to changes in temperature or pressure. Together, these tools have the potential transform the chemistry-based high temperature geosciences into a discipline also rooted in physics and material science. The first proposed project will combine synchrotron microdiffraction with Raman spectroscopy to directly correlate crystal structure with Raman band position. Such efforts will define how crystal structure and deformation mechanisms change with changing pressure-temperature conditions. Second, pink deformation bands in rare, financially valuable diamonds will be measured using synchrotron microdiffraction. Results will identify the origin of pink color in diamonds, and importantly, constrain strain rates and stresses in the Earth’s deep lithospheric mantle. Finally, Raman thermobarometry will be performed on samples collected across a full transect of a crustal section at the Famatinian Arc, Argentina. The reliability of Raman estimates will thus be tested against critical stratigraphic constraints and independent thermobarometers. Each project provides new constraints on mineral deformation mechanisms and mechanical processes active in the subsurface. Students working on this project will be prepared for careers in academia or industry as leaders in spectroscopy, diffraction, crystallography, and geovisualization. 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.