NSF Award
2313679
The minerals zircon (ZrSiO4) and baddeleyite (ZrO2), although present only in low concentrations in most rocks, are important phases in geochronometry (measuring ages of rocks, meteorites, and geologic events). They incorporate trace and minor elements useful as geochemical indicators. Zircons in particular are very robust mineral grains and, since they can survive many types of geological events, are some of the oldest known materials on Earth. They have preserved information about geological processes that were occurring up to 4.4 billion years ago. Understanding the diffusion (mobility of atoms) behavior of key elements inside these minerals provides major constraints on how we interpret the measured ages, and chemical signatures of rocks and ancient geological events. There has been extensive study of diffusion of several chemical elements in zircon, even if some elements have been understudied. In contrast, there is a lack of diffusion data entirely for baddeleyite, which can yield complementary information to that gained from zircon analysis. Understanding diffusion in these minerals is essential for interpreting a wide range of geochronometric data, and evaluating and interpreting the chemical and isotopic signatures retained in these minerals over geologic timeframes. The main broader impacts of this work will be a contribution of important data that can be used by a wide range of scientists in diverse, but related, fields. The project will also provide an educational experience for undergraduate students in physics, engineering, and geosciences, as well as high school students from underserved communities. <br/><br/>The proposed experiments build on a body of work measuring diffusion of a variety of elements in accessory minerals (minerals in generally minor abundance in rocks, but which incorporate elements important as geochronometers or geochemical tracers), to obtain a more complete geochemical picture of these critical minerals. The work also continues the refinement and application of accelerator-based ion beam techniques (Rutherford Backscattering Spectroscopy and Nuclear Reaction Analysis) in diffusion studies, exploiting the superior depth resolution of these analytical methods to access the slow diffusivities characteristic of many species in these materials. With the increasing application of microanalytical techniques to analyze natural samples and access fine-scale chemical and isotopic variations, diffusion data are a critical parameter in interpreting timing of geologic events, and evaluation of past chemical environments and thermal histories. These measurements will yield critical information for interpreting isotopic ages and thermal histories for baddeleyite, a mineral of interest but for which little diffusion data currently exist. The measurements of pentavalent cation diffusion in zircon will provide information about the resistance to chemical alteration of elements potentially useful as geochemical tracers, provide insight into substitutional mechanisms and charge balance for diffusion of altervalent cations. The Xe diffusion results may have implications for better interpreting Xe isotope systematics and noble gas behaviors in terrestrial and lunar samples, and understanding histories of the early Earth and Solar System. Zirconia also has utility as a refractory and optical material, so better understanding of its properties may have technological implications. The broader impacts of this work will be as a contribution of important data that can be used by a wide range of scientists in diverse, but related, fields in the geosciences, including thermochronology, geochronology, and studies of the early Earth and Solar System. The project will involve undergraduate students in research, providing experience in preparing samples, crystal synthesis, conducting experiments, using various analytical methods, and analyzing and interpreting data and presenting at research conferences. The project will also support a community outreach effort aimed at introducing local high school students to scientific research methods and Earth science.<br/><br/>This project is jointly funded by Petrology & Geochemistry and Division of Earth Sciences to support projects that increase research capabilities, capacity and infrastructure at a wide variety of institution types, as outlined in the GEO EMBRACE DCL.<br/><br/>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.
