Planetary Petrology and Cosmochemistry: In this area I focus on evaluating and quantifying the processes that changes the planetary chemistry. In effect, I try to ask how we can use the behavior of specific elements (Cl, F, S, C, H, OH) to understand the origin and evolution of planetary bodies. I work on a wide range of problems related to the high temperature crustal evolution of Moon, Mars, and other small planetary bodies such as chondrules and Ca-Al-rich inclusions (CAIs) and the role of volatiles and fluids on this. The approaches that I use range from analytical studies of Martian, lunar, and primitive meteorites to experimental simulation of a variety of magmatic processes. The specific areas that I conducted planetary research include degassing of lunar magmas, phase equilibria studies on the role of volatiles in changing mineral/melt equilibria in Martian magmas, and magmatic fluid/wall rock interaction in the Martian crust. Some recent highlights include the flash melting experiments implemented as time-series studies on synthetic chondrule compositions to explore the behavior of halogens in the volatilization of alkalis during chondrule forming processes and Cl, F apatite-melt partitioning experiments at low pressures which are fundamental to the use of apatite in assessing volatile abundances of planetary interiors, especially the Moon and Mars.
Two recent projects that I am working on are simulating hydrothermal activity on Mars and constraining apatite crystal structure with phase equilibria experiments.
Even though rover and orbital Martian missions provided a wealth of information on igneous and sedimentary processes of the Martian surface, we still do not understand the origin of the high concentrations of metals, sulfur and halogens (Cl, Br) in Martian breccias at Gale Crater relative to their abundances in Martian meteorites. My research on Mars hydrothermal activity started with the thesis work of my graduate student Alexander Rogaski and involved degassing experiments to investigate volatility of Germanium (Ge), Lithium (Li), and Zinc (Zn) deposits in Martian basalts(Rogaski et al., 2019, LPI Contribution No. 2132, Abs. #2864; Ustunisik et al; 2018, LPI Contribution No. 2883, Abs. #2659). We developed an experimental hydrothermal fumarole model to simulate chemical interactions between outgassed vapors and minerals present in Martian soil to understand these enrichments using surface coatings (rocks and soil samples) from the Gale Crater on Mars. Combining new partitioning and solubility studies with our recent results will allow estimation of the contribution of volcanic degassing to enrichments of S, Cl, Ge, Zn, and Cu at the Martian surface as a global process using Gale Crater as a local example.
Another focus of my planetary research involves understanding the behavior of volatiles in extraterrestrial materials by conducting experiments on the mineral apatite - the only volatile-bearing phase that is ubiquitous in extraterrestrial materials. Apatite can be used to reconstruct the composition of the Solar System?s earliest fluids (apatite-based melt-hygrometry), volatile abundances in planetary bodies (Moon, Mars), and habitability of past environments on Mars only if we have a quantitative understanding of how volatiles such as Cl, F, and OH partition between phases (apatite, melt or fluids). My experiments constrained the crystal chemical effect and role of varying temperatures on Cl-F partitioning between silicate melt and apatite (McCubbin and Ustunisik, 2018, American Mineralogist) to have a better understanding of mineral-melt partitioning relationships in portions of apatite compositional space where volatile components of different crystallographic sites undergo non-ideal mixing. Our reassessment on the forbidden region within apatite F-Cl-OH ternary space documented where apatite compositions should not be used for apatite-based melt-hygrometry. Furthermore, we demonstrated that even though apatite has specific crystallographic site accommodations for volatiles that are amenable to the use of apatite for melt-hygrometry, apatite-melt exchange coefficients can vary as a function of temperature, pressure, melt composition, and/or oxygen fugacity.
My experiences in planetary geology has convinced me that many of the approaches used exclusively either in planetary or terrestrial petrology could profitably be transferred between fields. With the many recent successful NASA missions, much can be done to make a quantum leap forward in our knowledge of the formation and evolution of planetary bodies.

Petrology and Volcanology of Arc Magmas: I am interested in quantification of processes that control magma evolution at the depth (evolution of mantle chemistry) as well as in shallow plumbing systems (formation and differentiation of continental crust) underlying active stratovolcanoes. My focus is sorting out the geochemical signals that are imposed by various differentiation processes (e.g, crystallization, decompression/degassing, magma mixing/recharge, filter pressing, density-driven convection) and evaluate their relative roles and timing in different magmatic systems. The techniques applied are similar to those used for the investigation of MORB, specifically the microanalysis and trace element geochemistry of phenocrysts and melt inclusions). My most recent work in the Oregon Cascades focused on using phenocrysts microchemistry and strategic sampling of a single eruptive unit from Mt. Jefferson(Ustunisik et al., 2016 G-cubed). What we found was that the magma chamber was stratified mineralogically, but not geochemically. In addition, the composition, and the presence or absence of amphibole indicated that the top of the magma chamber was ~4 km depth, with the bottom close to 10 km depth. This is similar to the depth and size of other magma chambers in the Cascades at currently active centers (Mt St Helens) - but determined using a completely different approach (e.g., mineral chemistry and phase equilibria vs. geophysics). The future direction of my arc research involves collaboration with geophysicist colleagues at SD Mines focusing on Okmok Volcano in the Aleutians. This project will attempt to apply techniques from both petrology and geophysics to understand the characteristics, depth and time frame of activity at Okmok. Our approach will involve an interdisciplinary application of geophysical constrains on geometry and deformation with petrologic constrains on pressure and magma dynamics.
As I study evolution of magma systems associated with convergent margins, some of the questions that I ask are:
1. What causes the magma diversity on continental crust in arc magmas?
2. What is the role of volatiles and fluids in this diversity by:
a) controlling the chemical evaluation of silicate melts and
b) generation of ore deposits through late-stage hydrothermal and mineralization processes?
3. How do vast archives of information recorded by minerals help to understands hazards of subduction zones such as volcanic eruptions and earthquakes?

Petrology of Mid-Ocean Ridge System: The mid-ocean ridge (MOR) system is the largest geological phenomena on Earth, making up over 70% of Earth?s crusts. The forces that drive this system affect essentially all surficial processes on Earth, from volcanoes to plate tectonics and earthquakes, climate change, and geomorphology. My focus is on understanding processes that produce the range of compositions of lavas observed. In detail, I use phase equilibria, composition, and textures of plagioclase megacrysts from a specific class of MORB - plagioclase ultraphyric basalts (PUB) to constrain the heat and mass balance of ridge systems (extent of melting, fractionation, mixing, degassing). I approach the question of their petrogenesis, and what they can tell us about the broader issue of the formation of the oceanic crust, by 1. conducting experiments to determine their phase equilibria - required in order to build quantitative models of crustal formation, 2. studying the composition of plagioclase-hosted melt inclusions with the goal of understanding the characteristics and depth of formation of megacrysts, and 3. systematically studying plagioclase textures with respect to major and trace element characteristics to identify processes occur within the magma plumbing system and their relative importance. My high-pressure experiments on PUB lavas documented extremely high CO2 contents consistent with these megacryts? formation in the upper mantle and the presence of an unanticipated anomaly in PUB phase equilibria that, taken together, supported the idea that PUB lavas represent one of the few opportunities to sample products of mantle process under ridge systems (Ustunisik et al., 2021 in-review G-cubed). The significance of this finding has broad implications for understanding issues as diverse as the C budget of the mantle (necessary to model global CO2 flux) and the extent of melting that produces oceanic crust and results in seafloor spreading and continental drift (the driving force for all geology on the Earth?s surface). My graduate student Kristen Lewis? work has shown that the process by which we treat melt inclusions (MI) (homogenization) has a significant impact on the geochemical signal represented in inclusions and in turn, how we interpret data from MI in our models of MORB petrogenesis (Lewis, Ustunisik et al., 2021, Frontiers in Earth Science). These studies also contributed to our review paper that summarizes best practices for preparation, analysis, and data presentation from silicate melt inclusions (Rose-Koga, Ustunisik et al., 2021, Chemical Geology). Recently my research in this area has been funded by 2 grants from the South Dakota Boards of Reagents (SD BOR) focused on measurement of volatile and trace element compositions of MIs with the goal of better understanding mantle melting, reactive transport and the CO2 budget of the mantle. Our recent paper (Nielsen, Ustunisik et al., 2020, G-cubed) documented the spatially distributed heterogeneity recorded in plagioclase megacrysts in PUB, and interpreted the result to be a consequence of the extent and character of magmatic heterogeneity within the crust and upper mantle. This funding is supporting the research of my current graduate student John Hewitt, who is continuing this research.

Geochemical Controls on Carbon Sequestration: Human related emissions of atmospheric CO2 are a major factor driving global warming. Mitigation efforts involve either replacing fossil fuels as energy sources, and/or reducing existing levels of atmospheric CO2 through capture and storage. Recently large-scale field studies showed that cation-rich mafic and ultramafic rocks can sequester CO2 through carbonate mineralization by increased pH induced by CO2 injection. Yet, the geochemical mechanisms and kinetics of this process are poorly understood at the laboratory scale. As a part of a newly funded NSF-CBET project, I have become involved in this research as a co-PI with colleagues in the Civil and Biological/Chemical Engineering departments at SD Mines. I design pore- and core-scale experiments in the Experimental Petrology laboratory to sequester CO2 through carbonate mineralization (e.g., calcite, magnesite, dolomite) from basalt and peridotite as a function of temperature, pressure, time, and starting composition. The project?s goal is to use extreme pH conditions induced by CO2 injection, together with the addition of extremophile bacteria, to drive bioaugmented reactions.

Big Data Petrology: Quantitative predictive models for trace element behavior require large experimental data sets due to the dependence of partitioning behavior or trace elements on temperature, pressure and composition. In addition, to model complex natural systems one must have predictive models for every trace element of interest between every mineral crystallizing or melting in the system. My goal is to understand how the precision of this complex set of predictive models are dependent on the data with which models are calibrated. Our most important finding to date is that experimental datasets are not internally coherent. For example, the number of experimental determinations differs from element to element and equally important, the composition of the population varies with different elements. This means that any regression analysis must see through these differences to be applicable to a wide range of compositions. Failure to accommodate the observed uneven distribution of data results in an internal bias in trace element partitioning models. I have been continuously funded as a PI in 3 NSF projects (OCE/MGG, MGG, EAR, and EarthCube) to lead research with the LEPR (Library of Experimental Phase Relationships) and traceDs under IEDA (Interdisciplinary Earth Data Alliance). All of these projects involve collaboration with a team of colleagues working independently on a series of interlocking goals. Over the past years, these grants provided funding for summer salary for my graduate students and funded a post-doc (Jay Tung) working on statistical analyses of experimental datasets. In the past few years, this work has resulted in a number of presentations at national meetings, workshops, and publications (Nielsen, Ustunisik et al., 2017, G-cubed; Ustunisik et al., 2019, Geochimica Cosmochimica Acta). My most recent effort involves my graduate student, Erica Cung, whose thesis centers on determining how to predict dependencies as well as possible biases related to data configuration. To date, we have compiled data from over 15,000 experiments and are in the process of developing an interface that will provide investigators access to information that was previously distributed across over 700 different publications - all in formats that differed from one another. Our goal is to provide a coherent source of shared information that will enable future research to begin at a shared starting point.

Grant Funding: