The first project investigates diverse magmas erupted over the 35 ky known history of Hayes Volcano in south-central Alaska. Three distinct magma types are delineated. Two of these have adakite-like compositions (elevated Sr/Y and depleted heavy rare earth elements) while the other is non-adakitic. These magmas are modeled to be products of fractional crystallization accompanied by assimilation of diverse materials best explained by varying ascent pathways and polybaric differentiation from the same mantle source. Their generation is directly controlled by the geometry of the Pacific Plate beneath Hayes. Additionally, shared isotopic and trace element compositions of Hayes and Mount Spurr define a common mantle source. This study provides new insights into the production of varied magmas along the Aleutian-Alaskan arc.
The second project tests the feasibility of tracing past uranium (U) contamination in the growth rings of trees. Like other metals, U mobility in annual growth rings is dependent on the tree species. Uranium abundances and isotopic compositions were measured in sugar maple, black walnut, slippery elm, and white ash tree rings near the former Fernald Feed Materials Production Center (FFMPC), a U purification facility in Ohio. U concentrations, 235U/238U, and 234U/238U in sugar maple are generally consistent with known events in FFMPC history suggesting that this species is reliable for monitoring past U contamination. However, U isotopic compositions (including 236U/238U) do not correspond to known events in black walnut, slippery elm, and white ash tree rings; therefore, U must be mobile across annual growth rings in these species. Nevertheless, the youngest growth rings in sugar maple and slippery elm are isotopically similar to contemporary soil compositions suggesting that these species may be used to monitor current, bioavailable U contamination.
The final project uses lichen to trace the spatial extent of past, cryptic airborne industrial and nuclear contamination. Mound Laboratories (Ohio) operated from 1946 to 1996 performing weapons, energy, and space exploration research and development. Lichen samples from within 5 km of the site contain high concentrations of Pb, Zn, and Cu but low concentrations of U and Th. While the major U isotopes are within error of natural U, positive correlations between U concentrations, 236U/238U, and 230Th/232Th provide robust evidence that enriched U and non-natural Th were released into the surrounding area. These results further illustrate that lichen are powerful archives of contamination and that the determination of isotopic compositions is essential to constrain the presence of anthropogenic inputs.