I just finished my first 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 melt during magma cooling. Apatite is a calcium phosphate mineral that incorporates sulfur into its structure during crystallization. How much sulfur depends on a few factors, but the amount of free oxygen in the system, or redox state, plays a big role. Sulfur is present in multiple oxidation states, or species, depending on the redox state of the system: sulfide (S2-), sulfite (S4+), or sulfate (S6+). 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 sulfur species. That discovery resulted in Brian doing experiments to understand the incorporation of sulfur into apatite in a primitive, mafic magma composition across a range of redox states. He related the proportion of S6+/total sulfur (S6+, S4+, S2-) to the redox conditions of the magma, proving 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 am spending the months of June and July 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’m running a total of 5 experiments, each at a different controlled redox state, for 3 days each. I am crystallizing apatite from a dacitic melt in the internally heated pressure vessels, then analyzing the run products this fall using the Electron Probe Micro-Analyzer to quantify the compositions of the apatite and melt and will measure the sulfur species present in apatite using a synchrotron light source at Argonne National Lab in Chicago or Brookhaven National Lab on Long Island.
This study 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.
I am currently in Hannover running my experiments! Check out this post on the first week and details of how my experiments work, while this post gives an update halfway through. Hannover is a nice city to work in, and the area I live is full of students, parks, and biergardens for when I’m not in the lab.
I’ve done a little traveling and outreach already this past year – see the following posts: