Collaborative Research: The Zirconium Isotope Composition and Variability of the Silicate Earth -- A Pilot Study

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Over the past 60 years the element zirconium (Zr) has been increasingly used as a tool for deciphering the differentiation history of the Earth and other 'rocky' planetary bodies in our Solar System. Despite being a 'trace element' (i.e., element of relatively low concentration) in most geological environments, its preferential enrichment in the chemically differentiated portions of the terrestrial planets - like Earth's continental crust - plays a key role in the presence of accessory minerals like zircon (ZrSiO4) and baddeleyite (ZrO2). In addition to being a cornerstone in the study of geologic time using the Uranium-Lead geochronometer, these accessory minerals are the main carriers of zirconium in the crust and are thus likely to preserve a unique yet unexplored record of the evolution of Zr isotope composition through geologic time. As such, understanding the processes that lead to variability in the isotopic composition of zirconium and how this is recorded in Zr-rich accessory minerals, may provide a window to explore the geochemical evolution of our planet in the deep geologic past, even beyond the oldest preserved rock record currently known in our planet.Shifts in the bonding/coordination environment of tetravalent Zr ions in silicate magmas during zircon and baddeleyite crystallization are expected to result in fractionation (i.e., differential equilibrium incorporation) of its isotopes in precipitated solids and residual melts. This implies that small variations in the abundance of zirconium stable isotopes in terrestrial rocks and minerals have the potential to elucidate how this element behaves and fractionates in high-temperature geological environments. This award will support two early-career investigators to develop techniques to measure zirconium isotopic compositions at high precision and explore, for the first time, the stable zirconium isotopic composition of silicate Earth. The principal goals of this research are threefold: 1) To develop the laboratory materials (e.g., isotopic reference standard and isotopic tracers) necessary for making zirconium isotopic measurements at high-precision. This will be accomplished in collaboration with scientist from the National Institute of Standards and Technology (NIST), who in the future will continue to distribute the standard materials produced during this research; 2) To explore the range of variability in zirconium isotopic abundances of key reservoirs that comprise the solid Earth; 3) Using the newly gained knowledge, explore how variations in the isotopic composition of Zr may be linked to the development, evolution and chemical refinement of the Earth's crust.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.