Critical Mineral Resources and the Energy Transition

To sustain a peaceful and healthy world of 7 billion people requires access to energy and other natural resources. Motivated by the desire to reduce the environmental damage caused by our consumption of fossil fuels, there is a push to transition our energy sources to “renewables”. Energy production and storage and an efficient electrical infrastructure are key to making this transition, but expanding in this arena taxes other natural resources, such as copper for our electrical grid, rare earth elements for wind turbine magnets, and lithium and cobalt for batteries. The critical metals, unfortunately, are in short supply and unequally distributed around the world, leading to complex geopolitics and national security challenges. Extraction of these mineral resources come with their own types of environmental damage, mostly centered around habitat destruction and pollution of the environment. Our work here focuses on understanding how critical mineral deposits form, bringing together geology, geochemistry, surface process, earth history and the physics of fluid transport. Understanding the origins of such deposits is essential for discovering new resources as well as making recommendations on how to more efficiently extract metals so that environmental damage is minimized.

Acoustic monitoring of wildlife

The great majority of migratory birds migrate at night when you can’t see them. This is the invisible dark migration. Understanding the migratory patterns of birds is one way to assess how changes in land use and climate influence the natural environment. We have established a series of near continuous acoustic monitoring stations, which pick up the nocturnal flight calls of migrating birds. We analyze these calls to build a record of the life that flies over in the night sky. We are always interested in working with computer scientists and dedicated bird enthusiasts in growing our network and analyzing the data.

We are also working on using acoustic monitoring to provide objective constraints on the health of ecosystems. Of interest is how to measure ecosystem health from land use changes, such as from destruction or restoration of habitats. The next several decades will see a proliferation of a carbon tax and credit economy, but there are few protocols for properly assessing ecosystem health at scale. Bioacoustics provide one way to groundtruth various methods of monitoring carbon storage and ecosystem health.

Finally, we are dedicated to making the observation of wildlife, particularly birds, more accessible to general public. We develop better methods for identifying birds in the field, with a particular emphasis on birds that are so similar that field separation has historically been challenging. We have worked on pipits, female orioles, pewees, dowitchers, cormorants and loons. At present, we are contracted to produce a three part series of identification guides focused on the field separation of North American flycatchers. Our upcoming field guides will introduce a new method for observing birds and we hope this is the beginning of a new field guide format.

Planetary crust formation

Half of Earth's radioactive heat producing elements like U, Th and K have migrated into the continental crust over the course of Earth's history.  However, the crust makes up less than 0.5 % of the Earth. Primary magmas are generated in the mantle and eventually migrate to the Earth's surface, cooling, crystallizing and differentiating into a wide diversity of magma types.  Felsic liquids rise to the surface and mafic cumulates are left behind in the lower crust.  What are the mass fluxes of juvenile crust formation, felsic liquids and cumulates?  How do these processes distribute various elements throughout the Earth?  How have these processes changed with time?  Our research on this topic is based on field work, geochemistry and geochemical and geodynamic modeling.  Of interest in our working group is the origin of Archean and Phanerozoic continental crust, the role of arcs in generating crust, and the nature of crust formation on other planets, such as Mars.

Continental Lithospheric Mantle Evolution

We are interested in the origins of the continental lithospheric mantle, which is that part beneath the crust that is rheologically strong enough to translate with the overlying crust. The crust and lithospheric mantle together constitute our tectonic plates. Of particular interest are the origins of cratonic mantle. The deep roots of cratons are made of peridotitic residues of melt extraction. These cratonic roots are cold and should be unstable, but the chemical buoyancy associated with the peridotites compensates, in part, the effects of thermal contraction. Of interest to us are how cratonic peridotites actually form. What are the temperatures and pressures of formation, tectonic environments, etc? What is the density structure of cratonic mantle? When was melt extracted? What are the seismic properties of lithospheric mantle? What controls the rheology of the lithospheric mantle? How has the compositional and thermal evolution of the lithospheric mantle over Earth’s history manifested in terms of Earth’s surface topography through time.

Physical processes of magma generation, differentiation and extraction

We are interested in how crystallization and crystal-melt separation drive the differentiation of magmas. We approach this topic by combining geochemistry with simple physics. What conditions (water, oxygen fugacity, temperature, pressure) control the crystallization path of a magma and what do different geochemical differentiation trends tell us about the nature by which magmas are transported in and through the crust. For example, why do magmas become more iron-enriched during differentiation in mid-ocean ridge environments and iron-poor in continental settings? This dichotomy in iron evolution plays a significant role in the redox evolution of planetary crusts and surface with implications for the availability of nutrients and the long-term composition of atmospheres. Understanding differentiation paths also are also central to understanding the origin of certain ore deposits, particularly those critical to the energy transition.

From the physics perspective, we also work on how melts segregate from crystals. While segregation, in its simplest form, is driven by buoyancy forces associated with density contrasts, it is the combination of buoyancy, over-pressures and the fluid dynamics of melt transport that ultimately dictate how fast melts are removed. The problem that interests our group the most is how melts accumulate quickly to lead to catastrophic volcanic eruptions or form explosive underground ore deposits. In most cases, the melts or fluids of interest appear to derive from crystal-rich mushes, wherein viscous stresses dominate and extraction should be a very slow process in general. Our research focuses on quantifying the rates of these processes and developing simple models for how melts are transported through thin dikes and sills.

Long-term climate evolution

The composition of Earth’s atmosphere on long timescales is controlled by inputs of key volatiles from a planet’s interior and outputs from the atmosphere through biogeochemical processes, reaction with the crust or atmospheric loss. Our interests lie in the whole Earth cycling of carbon, sulfur, oxygen and various nutrients, such as P. How does the thermal evolution and the nature of magmatism and metamorphism control the deep Earth drivers of these cycles? How does crust formation modulate some of these sinks? How does the combination of magmatism and tectonics alter the Earth’s surface to control topography, which controls erosion and the formation of basins for sequestering some of these volatiles and nutrients? In this work, we track how volcanism changes with time by studying the eroded remnants of ancient volcanoes as well as well characterized ash layers in marine sediments. We also perform simple box models to describe whole Earth elemental cycles, taking into account deep Earth degassing and chemical weathering.

Crystal Growth Kinetics

How do large crystals grow? These are childhood questions that we pursue. We develop geospeedometers to clock the rates of crystal growth. With these rates, we can gain a better understanding of the dynamics of magma chambers or hydrothermal systems, which have implications for how volcanoes erupt, mineral deposits form, and beautiful gems form. Crystallization often releases latent heat. We are exploring possibilities of storing energy in supersaturated solutions and crystallizing these solutions to release the stored energy in the form of heat, which we can harness to do useful work. Understanding crystal growth kinetics is a key step towards controlling the rates of energy release.