Major Element & Isotopic Equilibrium During Metamorphism
Most metamorphic studies rely on equilibrium thermodynamics for determining pressure and temperature, and constructing P-T-t paths. Therefore, it is important to know how closely rocks approach equilibrium. In addition, many crystal nucleation and growth studies are dependent on knowing which if any elements reach equilibrium and determining the equilibrium volume during these processes. Garnet age zoning and elemental zoning provides a test for nucleation and growth models. Work by one of my recent Ph.D. students and colleagues establish a quantitative correlation between Sm-Nd age zoning and Mn zoning in garnet crystals throughout a pelitic schist sample (Gatewood and others, Chemical Geology, 2015). The isotopic analyses for this project included numerous garnet grains and up to five separate concentric samples from compositional zones radially arranged from core to rim in individual grains. Current plans include using 3d X-ray tomography, collected for the equilibrium study, for construction of nucleation and growth models. This work has been funded by National Science Foundation Petrology and Geochemistry.