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We explore the geologic history of Earth's lithosphere by integrating field work, geo/thermochronology, petrology, and geochemistry. We are particularly interested in the thermal and tectonic evolution of continental lithosphere, with a focus on decoding the complex, poly-metamorphic rock record of crust evolution through Earth history. Below are a few current research ventures.
Migmatite from the Ivrea Zone, IT. Field evidence of partial melting and differentiation in the deep crust. Hand lens for scale.
Deep crustal processes
Deep crustal processes
The thermal and mechanical state of the lower crust plays a defining role in the evolution of magmatic and tectonic systems. We study deeply-exhumed metamorphic terranes and xenoliths—fragments of the deep crust brought to the surface by volcanism—to reconstruct pressure-temperature-time histories of the lower crust. This is done using "petrochronology", the integration of petrological, geochemical, and geochronological data. We use these data to understand heat transfer in the lithosphere, crust composition, and the dynamics of ancient mountain belts.
Field work in central Tanzania, sampling Archean rocks. Standing on deformed orthogneiss near Dodoma.
Continents in deep time
Continents in deep time
Cratons are the old, stable interiors of continents that have survived tectonism and magmatism for billions of years. Cratons also host the oldest record of crust formation and life on Earth. How did cratons form and stabilize? Were the processes that formed the earliest continents similar to modern plate tectonic processes? To study ancient processes, we look at ancient rocks. Projects are based in various cratons (Tanzania, Siberia, Wyoming) and utilize the highest-precision and highest-resolution geochemical and geochronological tools (CA-ID-TIMS, LA-ICP-MS depth profiling, etc.) to firmly establish the conditions and timing/rates of geological processes that occurred in the deep past.
Scanning electron microscope (SEM) image of an unpolished apatite crystal with a laser ablation depth profile pit (used for measuring near-rim chemical zonation). The laser spot is 50-microns in diameter and ~10 microns deep.
Technique development
Technique development
We work to develop new geochemical and geochronological tools for geoscience research. We are particularly focused on improving our ability to measure the ages and compositions of minerals using in situ microbeam methods (LA-ICP-MS, SIMS, etc.) to better address tectonic, magmatic, and paleo-environmental questions.
Top image: Having lunch atop the Panamint Mountains, CA
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