Bryan Alan Killingsworth Justin A. Hayles 2022 <p><span>Isotopic&nbsp;disequilibrium&nbsp;is not as well constrained as equilibrium, hindering interpretation of isotopic variations. Kinetic&nbsp;isotope effects, a subset of disequilibrium, are common in nature and have been assumed to be distinct from equilibrium and mass independent isotope effects based on underdeveloped criteria. Using basic physical principles, we provide needed mechanistic constraints on mass-dependent kinetic isotope effects for the triple&nbsp;oxygen isotope&nbsp;system. We find some kinetic isotope effects yield large isotopic variations, exceeding equilibrium, which could be mistaken for mass independent relationships. Meanwhile, other kinetic isotope effects are found to have triple oxygen isotope relationships that could be mistaken for equilibrium isotope effects. Comparison against prior case studies of&nbsp;thermal decomposition&nbsp;of&nbsp;calcite&nbsp;(CaCO</span>₃<span>) and&nbsp;brucite&nbsp;(Mg(OH)</span>₂<span>) further tests our results. Although oxygen is the focus here, our approach applies to any system with more than two isotopes.</span></p> application/pdf 10.1016/j.chemgeo.2021.120646 en Elsevier Constraints on triple oxygen isotope kinetics article