Research

There are several elements that exist in more than one oxidation state in Earth's mantle, and the most important of these affecting phase stability are iron, carbon, and sulfur. Variations in the oxidation states of these elements affect the compositions and abundances of different minerals or the depth at which melting occurs. Much of what is known about the oxidation states of these elements in Earth's mantle comes from chemical analysis of the basalts that have erupted at Earth's surface, but which were generated in the mantle. Our group performs experiments under controlled-atmosphere conditions in the gas-mixing furnace or at high-pressure using novel containment techniques to control the redox environment in the piston cylinder to understand process that are operating in the mantle. We then compare our results to natural basalts to better understand what the surface geologic record is telling us about the hidden process of the mantle.

Researchers in the UMD Experimental Petrology Lab analyze the oxidation state of Fe in experimental products using electron microprobe (EPMA) and X-ray absorption near-edge structure (XANES) analysis, which is a synchrotron-based technique.

It isn't all experimental work. We also investigate the chemistry of natural basalts and peridotites, especially in collaboration with partners at the Smithsonian Institution, Berea College, the University of Delaware, and the University of Rhode Island.

Relevant publications:

Davis, FA, Cottrell, E, 2021. Partitioning of Fe₂O₃ in peridotite partial melting experiments over a range of oxygen fugacities elucidates ferric iron systematics in mid-ocean ridge basalts and ferric iron content of the upper mantle. Contributions to Mineralogy and Petrology. 176, 67. DOI: https://doi.org/10.1007/s00410-021-01823-3

Cottrell, E, Birner, SK, Brounce, M, Davis, FA, Waters, LE, Kelley, KA, 2021. Oxygen Fugacity Across Tectonic Settings. AGU Geophysical Monograph: Redox variables and mechanisms in magmatism and volcanism. DOI:

https://doi.org/10.1002/9781119473206.ch3

Birner, SK, Cottrell, E, Warren, JM, Kelley, KA, Davis, FA, 2021. Melt addition to mid-ocean ridge peridotites increases spinel Cr# with no effect on recorded oxygen fugacity. Earth and Planetary Science Letters. 566, 116951. DOI: https://doi.org/10.1016/j.epsl.2021.116951

Birner, SK, Cottrell, E, Warren, JM, Kelley, KA, Davis, FA, 2018. Peridotites and basalts reveal broad congruence between two independent records of mantle fO2 despite local redox heterogeneity. Earth and Planetary Science Letters. 494, 172-189. DOI: https://doi.org/10.1016/j.epsl.2018.04.035

Davis, FA, Cottrell, E, 2018. Experimental investigation of basalt and peridotite oxybarometers: implications for spinel thermodynamic models and Fe3+ compatibility during generation of upper mantle melts. American Mineralogist, 103, 1056-1067. DOI: https://doi.org/10.2138/am-2018-6280

Cottrell, E, Lanzirotti, A, Mysen, B, Birner S, Kelley, KA, Botcharnikov, R, Davis, FA, Newville, M, 2018. A Mössbauer-based XANES calibration for hydrous basalt glasses reveals radiation-induced oxidation of Fe. American Mineralogist, 103, 489-501. DOI: https://doi.org/10.2138/am-2018-6268

Birner, SK, Warren, JM, Cottrell, E, Davis, FA, Kelley, KA, and Falloon, TJ, 2017. Forearc peridotites from Tonga record heterogeneous oxidation of the mantle following subduction initiation. Journal of Petrology, 58, 1755-1780. DOI:

https://doi.org/10.1093/petrology/egx072

Davis, FA, Cottrell, E, Birner, SK, Warren, JM, Lopez, OG, 2017. Revisiting the electron microprobe method of spinel-olivine-orthopyroxene oxybarometry applied to spinel peridotites. American Mineralogist, 102, 421–435. DOI: http://dx.doi.org/10.2138/am-2017-5823

Birner, SK, Warren, JM, Cottrell, E, and Davis, FA, 2016. Hydrothermal alteration of seafloor peridotites does not influence oxygen fugacity recorded by spinel oxybarometry. Geology, G38113–1. DOI: http://dx.doi.org/10.1130/G38113.1

Earth’s mantle is compositionally heterogeneous owing to the combined effects of differentiation and recycling of surface material through subduction. The degree to which these chemical heterogeneities exist as distinct lithologies is critical to interpretation of the present state of Earth’s mantle and its development through geologic time, affecting, for example, interpretations of geophysical observations of the mantle and estimates of its temperature profile. We use high-pressure and high-temperature experiments to learn about melting processes in a heterogeneous mantle to connect geochemistry of erupted lavas to the compositions of their mantle sources.

The average composition of Earth’s mantle is similar to peridotite, a green, olivine-rich rock. However, the compositional diversity of basaltic lavas requires that the mantle be lithologically heterogeneous. Likely, recycled oceanic crust is also an important contributor to basalt petrogenesis.

Certain trace elements may have the potential to connect basaltic lavas to their mantle sources. In particular, the first-row transitions elements (FRTE) the elements from Sc to Zn on the periodic table, partition between mantle rocks and melts in ways that are sensitive to differences in source lithology. Researchers in the UMD Experimental Petrology Lab perform experiments to learn more about how these fingerprinting elements partition between minerals and melts.

We analyze FRTE in these experimental products using electron microprobe (EPMA) and laser ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS), especially in collaboration with partners at Florida State University.

Relevant publications:

Davis, FA, Humayun, M, Hirshmann, MM, Cooper, RS, 2013. Experimentally determined mineral/melt partitioning of first-row transition elements (FRTE) during partial melting of peridotite at 3 GPa. Geochimica et Cosmochimica Acta, 104, 232-260. DOI: https://doi.org/10.1016/j.gca.2012.11.009

Davis, FA, Hirshmann, MM, Humayun, M, 2011. The composition of the incipient partial melt of garnet peridotite at 3 GPa and the origin of OIB. Earth and Planetary Science Letters, 308, 380-390. DOI: https://doi.org/10.1016/j.epsl.2011.06.008

Humayun, M, Davis, FA, Hirschmann, MM, 2010. Major element analysis of natural silicates by laser ablation ICP-MS. Journal of Analytical Atomic Spectrometry, 95, 998-1005. DOI: https://doi.org/10.1039/c001391a