@article{THESIS,
      recid = {3680},
      author = {Chen, Xi},
      title = {Uranium Isotope Variations Tracing Oceanic Anoxia and  Zirconium and Hafnium Isotope Variations Tracing Planetary  Differentiation Processes},
      publisher = {University of Chicago},
      school = {Ph.D.},
      address = {2022-03},
      number = {THESIS},
      pages = {279},
      abstract = {This dissertation is part of the efforts in developing  novel non-traditional isotopic systems and applying them to  enhance our understanding of the histories of our Earth and  other planetary bodies. Specifically in this thesis I study  the uranium isotopic variations in marine sediments to  trace the oceanic anoxia in the ancient times, and I also  study the zirconium and hafnium isotopic variations in  igneous rocks and explore their potentials to trace  magmatic differentiation processes. U concentrations and  isotopic compositions of a large sample set of old-age  carbonates are measured and compared with compiled U  datasets of shales and young-age carbonates. Several new  modeling results are also presented to reconcile the  measurement results of ancient samples with the common  understanding of modern U oceanic cycle. This study points  out the invalidity of applying some assumptions of modern  models into the past time and also calls for more  interesting modeling and experimental work (Chapter 2).  
This dissertation also provides the first ab initio  calculation results of the Zr, Hf equilibrium isotopic  fractionation factors and they are readily to be used and  applied in many interesting questions. Several equilibrium  and kinetic modeling results are further presented to  explain the documented Zr isotopic variations in igneous  rocks and minerals. Our study shows that Zr equilibrium  isotopic fractionation is negligible during zircon  crystallization and magmatic differentiation, while the  diffusion-driven kinetic isotopic fractionation can readily  explain the actual observed data (Chapter 3). 
Finally,  this dissertation also presents an ongoing effort to  develop high-precision and high-accuracy Hf isotopic  measurements in individual zircon grains with low amount of  Hf available. The whole analytical procedure is improved  and this novel method will be further applied on lunar  zircons to provide better constraints on the  differentiation age of the Moon (Chapter 4).    
},
      url = {http://knowledge.uchicago.edu/record/3680},
      doi = {https://doi.org/10.6082/uchicago.3680},
}