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

在过去的60年里，元素锆（Zr）越来越多地被用作破译地球和太阳系其他“岩石”行星体分化历史的工具。尽管是一种“微量元素”（即，在大多数地质环境中，锆石（ZrSiO 4）和斜锆石（ZrO 2）等副矿物的存在，主要是由于其在类地行星的化学差异部分（如地球的大陆地壳）中的优先富集。除了是使用铀铅地质年代计研究地质年代的基石之外，这些辅助矿物是地壳中锆的主要载体，因此可能保存了地质年代中锆同位素组成演变的独特但未探索的记录。因此，了解导致锆同位素组成变化的过程以及如何在富含锆的副矿物中记录下来，可能会为探索地球在过去地质深处的地球化学演化提供一个窗口，甚至超过了我们这个星球上目前已知的最古老的岩石记录。在锆石和斜锆石结晶过程中硅酸盐岩浆中四价Zr离子的配位环境预期导致分馏（即，微分平衡掺入）的沉淀固体和残余熔体中的同位素。这意味着地球岩石和矿物中锆稳定同位素丰度的微小变化有可能阐明这种元素在高温地质环境中的行为和分馏。该奖项将支持两名早期职业研究人员开发高精度测量锆同位素组成的技术，并首次探索硅酸盐地球的稳定锆同位素组成。本研究的主要目标有三个方面：1）开发实验室材料（例如，同位素参比标准和同位素示踪剂）。这项工作将与国家标准和技术研究所的科学家合作完成，该研究所今后将继续分发在这项研究中产生的标准材料; 2）探索构成固体地球的主要储层的锆同位素丰度的可变范围; 3）利用新获得的知识，探索Zr同位素组成的变化如何与发展联系起来，该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响进行评估，被认为值得支持审查标准。

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.