Research Interests
I use geochemistry and geochronology to investigate the growth and destruction of the continental crust and the development of Earth’s terrestrial reservoirs through geologic time. My main tool of interest is the use of radiogenic and stable isotope systems to serve as ‘clocks in rocks’ and tracers of various processes, such as changes in magmatic source character or surface-deep earth feedbacks.
I consider field work, isotopic systems (U-Pb, Lu-Hf, Sm-Nd, K-Ar, stable O isotopes) and petrology to be engaging tool kits for characterizing these processes on multiple temporal and spatial scales, from individual outcrops to the subduction system. I also find questions related to possible deep earth-surface-climate connections in these settings to be intriguing, and am interested in how elemental budgets have varied across Earth reservoirs (ocean, mantle, atmosphere) both in the recent and ‘deep’ geologic past.
Big picture Themes I find Interesting:
Crustal Evolution: At what rate(s) has Earth’s continental crust grown and been destroyed through geologic time? What processes of melt extraction took place? What is the contribution of early crustal recycling to continental growth? How has the pace and style of crustal recycling and generation impacted other Earth systems (e.g. climate, weathering)?
Elemental Partitioning: How do magmatic and metamorphic events partition elements and isotopes between accessory mineral phases? How does this partitioning impact our interpretation of detrital datasets? (e.g. are accessory phases faithful recorders of whole-rock processes?)
Mineral Alteration: How do ‘damage’ domains in accessory phases impact our ability to interpret primary geochemical signals? How can we leverage micro-structural and micro-spatial information when interpreting isotopic measurements?
Analytical Methods for Geochemistry: How can we leverage coupled simultaneous isotopic measurements (e.g. Lu-Hf and U-Pb) to investigate Earth process problems? How can we couple radioisotopic methods (e.g. U-Pb or 40Ar/39Ar) with stratigraphic observations (e.g. astrochronology or climate records) to calibrate timescales and observations?
Check out my Google Scholar profile and read on below for Project Highlights
Bauer Earth Evolution Group (2020-2024)
Saglek-Hebron Complex, Labrador, Canada
Zircon cathodoluminescence (CL) images
Comparing Detrital and Igneous zircon records of early crustal evolution
(Beartooth Detrital Zircons)
The University of Wisconsin-Madison
Advisor: Annie Bauer
Collaborators: Tyler Blum, John Valley, Jonathan O’Neil, Hanika Rizo, European Research Council MEET Project
Although divorced from their parental rocks, detrital zircons are robust archives of primary magmatic and temporal information and record valuable chemical information about the earliest continents. However, questions remain regarding: (1) whether detrital grains adequately represent geologic processes through space and time and (2) if grains record processes from the full crustal thickness. During my time with the UW-Madison Earth Evolution Group I tackled these challenges by correlating in situ geochemical analyses within carefully-vetted grain domains and by applying my findings from suites of cogenetic igneous zircon as a geochemical framework to understanding Archean detrital data.
Archean Crustal Reworking: Insights from In Situ Zircon δ18O and Trace Elements
(Acasta Gneiss Complex + Saglek-Hebron Complex)
The University of Wisconsin-Madison
Advisor: Annie Bauer
Collaborators: Tyler Blum, John Valley, Jonathan O’Neil, Hanika Rizo, Chloë Bonamici, European Research Council MEET Project
Mixon, E.E, Bauer, A.M., O’Neil, J., Rizo, H. Blum, T.B., Valley, J. (2023). Mechanisms for generating elevated zircon δ18O in Archean crust: Insights from the Saglek-Hebron Complex, Canada. Earth and Planetary Science Letters. https://doi.org/10.1016/j.epsl.2023.118443
Plate tectonics drives the cycle of crust generation and destruction via volcanism, erosion modulated by uplift and climate, and recycling at subduction zones. While it has been posited that this cycle is intimately tied to the habitability of Earth, the continual recycling of crust (e.g. via impacts and eventually subduction zone processes) through Earth’s 4.5 billion year (Ga) history makes it challenging to investigate the nature of the earliest continents. Only about ~3% of Earth’s present surface is covered by rocks > 2.5. Of these, an even smaller fraction represents rocks as old as 4.0 Ga. As a member of the UW-Madison Earth Evolution Group I use a combination of in situ radiogenic (Lu-Hf, U-Pb) and stable (O) isotopes, trace elements (TEs), and petrologic observations to investigate and compare the processes responsible for forming the intact remnants of Earth’s earliest continents.
Detrital zircon grains + zircon reference materials in preparation for LA-ICP-MS and SIMS analysis.
Granitoid sampling location, Grand Canyon National Park
Zircon Lu-Hf Isotope systematics: A Lens on Volcanic-Plutonic Connections (Grand Canyon)
The University of Wisconsin-Madison
Advisor: Annie Bauer
Collaborators: Vishnu Basement Field Forum III Participants
Studies combining records of geochemical variation with observations of pluton structure and deformation are necessary to disentangle mechanisms and timescales influencing granitoid emplacement. I am working with an interdisciplinary group of geologists to disentangle these processes at the grain, sample, and crustal block scale using several plutons located in the Upper Granite Gorge of Grand Canyon as a natural laboratory.
WiscAr Lab (2018-2020)
Calbuco Volcano, Andean Southern Volcanic Zone (Chile, 2019).
Southern Andes Volcano Geochronology, Geochemistry, and Petrology
The University of Wisconsin-Madison
Advisor: Brad Singer
Collaborators: Brian Jicha, Adan Ramirez, Jake Klug, Paola Martinez
Mixon, E.E., Singer, B.S., Jicha, B.R., Ramirez, A., (2021) Calbuco, a monotonous andesitic high-flux volcano in the Southern Andes, Chile, Journal of Volcanology and Geothermal Research, Volume 416, https://doi.org/10.1016/j.jvolgeores.2021.107279.
Klug, J.D., Ramirez, A., Singer, B.S., Jicha, B.R., Mixon, E.E., Martinez, P. (2022) Intercalibration of the Servicio Nacional de Geologia y Mineria (SERNAGEOMIN), Chile and WiscAr 40Ar/39Ar laboratories for Quaternary dating. https://doi.org/10.1016/j.quageo.2022.101354
As a member of the WiscAr Lab for my first two years at UW-Madison, I worked to generate precise geochronologic data to constrain igneous processes. My 2018-2020 project focused on reconstructing the eruptive history of Calbuco Volcano (41.3°S). Using a combination of 40Ar/39Ar geochronology, geochemistry, petrologic observations, and field characterization, I developed a Pleistocene-Holocene eruptive history of this active frontal arc volcano and investigated hypotheses relating periods of episodically high growth rates to crustal stress changes governed by local to regional scale glaciation. This work has implications for understanding the spectrum of regional and local hazards, and also allows for hypotheses regarding solid earth-climate coupling.
WiscAr NGX-600 (installed 2019, upgraded 2020).
Isotopx NGX-600 Instrumentation PRoject
The University of Wisconsin-Madison
Advisor: Brad Singer
Collaborators: Brian Jicha, Damian Tootell, Brad Singer
Mixon, E.E., Jicha, B.R., Tootell, D., Singer, B.S. (2022). Optimizing 40Ar/ 39Ar analyses using an Isotopx NGX-600 mass spectrometer, Chemical Geology https://doi.org/10.1016/j.chemgeo.2022.120753
From 2019-2021, I worked to develop 40Ar/39Ar measurement routines for the WiscAr Lab’s recently acquired Isotopx NGX-600. Through this effort, I generated a three-prong approach to implementing best analytical practices for a new noble gas instrument, including: (1) identification of optimal measurement and integration times for blanks, baselines, and air aliquots of various ion intensities, (2) quantification of the NGX-600 sensitivity via measurements of first principle 40Ar/39Ar standards, and (3) development of corrections associated with inter-Faraday biases, instrumental mass bias, and Faraday-multiplier gain.