I am now in my second year of graduate studies at the University of Michigan in Ann Arbor. I joined the experimental petrology and economic geology lab group of Dr. Adam Simon in August 2018. My first PhD project focuses on understanding the behavior of sulfur in evolved magmas and how sulfur partitions between the mineral apatite and the magmatic melt. Apatite is a calcium phosphate mineral that incorporates trace amounts of sulfur into its structure during crystallization. How much sulfur depends on a few factors, but the amount of reactable oxygen, or redox state of the system, plays a big role. Sulfur is present in nature as multiple oxidation states depending on the redox conditions of the system: sulfide (S2-), sulfite (S4+), or sulfate (S6+), among others. Until a couple years ago everyone thought that apatite only took up sulfur as S6+, but then in 2017 Brian Konecke (a previous student of Adam’s who graduated with his PhD in Dec. 2018) was the first to measure S2- in apatite, proving that it incorporates more than one oxidation state of sulfur. That discovery drove Brian to do experiments to better understand the incorporation of sulfur into apatite in a primitive, mafic magma composition across a large range of redox conditions relevant to geologic systems. He related the proportion of S6+/total sulfur (S6+, S4+, S2-) to the redox conditions of the magma, showing that you can use sulfur in apatite to estimate the total initial sulfur in the magma as well as the redox state of the entire system – two things that are of utmost importance in geology!
My project builds on Brian’s work. I am conducting the same type of experiments that he did but am using an evolved (felsic) magma composition to assess the affect of magma composition on the behavior of sulfur. I spent 2 months in summer 2019 in Hannover, Germany, doing experiments at Leibniz University. The researchers in Hannover have amazing experimental facilities that we don’t have at the University of Michigan and have been collaborating with the Simon lab group for many years. I ran a total of 6 experiments, each at a different controlled redox state, for 3 days each. I crystallized the mineral apatite from a dacitic melt using internally heated pressure vessels, then analyzed the run products using the Electron Probe Micro-Analyzer to quantify the compositions of the apatite and melt and am in the process of measuring the oxidation states of sulfur present in apatite using a synchrotron light source. I’m in phase II of this project: I completed all my experiments, now I’m analyzing the run products! After I gather and process all the data (results), I will be in phase III — writing everything up.
This work is relevant to society because sulfur is critical in volcanic eruptions, the evolution of life on Earth, and the formation of many types of ore deposits. Sulfur is the 3rd most abundant component of fluids and vapors emitted by volcanoes and is much harder to study than water and carbon dioxide because it exists in multiple states in magma melts, minerals, and fluid/gas phases. As evidenced in Brian’s work, sulfur in apatite could provide a way to trace sulfur through the evolution of a magmatic system, something that has proven difficult and elusive to geologists studying volcanoes and ore deposits up to now.
See the following posts for info on some travel & outreach I did in year 1: