Metal stable isotope research
Molybdenum and uranium are redox sensitive elements. When in oxidized 6+ valence states, they are soluble, and their isotopes are prone to fractionation when dissolved Mo and U are removed from seawater. Consequently, sediments and altered basaltic oceanic crust can develop unique Mo (98Mo/95Mo) and U (238U/235U) isotope signatures depending on the redox state of the ocean. The two isotopes of thallium (203 and 205) also experience isotope fractionation when being scavenged from ocean water by sediments. These isotope signals should be carried into the Earth's interior when the sediments and oceanic crust are subducted. This begs the question: what happens to these Earth surface signals in subduction zones? Is nearly all Mo, U, and Tl transferred from the subducting slab into the mantle wedge, ending up in arc lavas? Are some of these elements carried deeper and ultimately mixed back into the convecting mantle, and if so, do additional isotope fractionations occur?
Research attempting to answer these and related questions has being conducted in collaboration Chris Reinhard (Georgia Tech), Noah Planavsky (Yale), and Jeremy Owens (Florida State). We're currently working on the Mo, U and Tl isotope chemistry of modern basalts from different tectonic settings. One particular focus area is the volcanic arc island of Martinique (Lesser Antilles). Catherine Chauvel has generously provided us with a suite a well characterized lava samples from the island, along with offshore IODP sediment samples that represent potential sediment input into the subduction zone. Results of the study of these samples are published in the paper listed below. We have also begun looking at how these isotope systems behave in subduction metamorphic assemblages (HP-LT rocks) in collaboration with Gray Bebout (Lehigh U).
Gaschnig, R.M., Reinhard, C., Planavsky, N., Wang, X., Asael, D., and Chauvel, C. (2017) Mo isotopes as a tracer of slab input in subduction zones: an example from Martinique, Lesser Antilles arc: Geochemistry, Geophysics, and Geosystems. Link