Igneous petrology through the lens of non-traditional stable isotopes

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It has long been recognized that geological processes can cause variations in the isotopic ratios of an element. For elements other than C, H, O, N, S, however, isotopic variations were thought to be insignificant at high temperatures. This perception changed dramatically about two decades ago, when advances in mass spectrometry revealed that isotopes of heavier elements (e.g., Mg, Fe) do, in fact, show resolvable variations in their isotopic compositions. These isotopic variations (or fractionations) provide a complement to chemical analyses and are especially useful in instances where chemical analyses provide ambiguous interpretations. Most studies are concerned with equilibrium isotope fractionations, in which the chemical and isotopic composition of the melts and crystals being studied do not change with time. My research program, however, focuses on kinetic isotope fractionation. This is the fractionation of isotopes that occurs as a system moves towards its equilibrium state. Kinetic fractionations are often large compared to equilibrium fractionations. My research program will use these unique kinetic signatures recorded within a single crystal, to determine how magmas beneath volcanoes evolve through time. Chemical variations within a crystal records changes in magmatic conditions (temperature, pressure, and composition) and, in some cases, can provide key information regarding the timeline of events leading up to an eruption. Measuring isotope profiles within a crystal using in-situ techniques, such as laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICPMS), can provide fundamental constraints on how, and on what timescale, a crystal obtained its chemical profile. Stable isotopes can also illuminate the history of inclusions found in these crystals. Using stable isotopes, the plumbing structure of a volcano - the geometry and timescales of magma movement below the surface - can be reconstructed with confidence. To achieve this goal, my group will work at the intersection of isotope geochemistry and experimental petrology, by simulating magmatic conditions in the laboratory and applying what we learn to natural samples. My research program will contribute to a fundamental understanding of the inner workings of active volcanoes.