Research interests

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Redox state of the solid Earth

My postdoctoral research is focused on constraining the redox state of the solid Earth using the behavior of multivalent elements as proxies for oxygen fugacity. Oxygen fugacity is a thermodynamic parameter that controls, to a first order, the structure of the planet and the chemistry of rocks, ores and the atmosphere. This research often takes my collaborators and I to the X-ray synchrotron beamline (Advanced Photon Source) at Argonne National Lab to characterize our samples. The above image shows a thin section of a rutile-bearing silicate glass. The red color is due to interactions between iron and oxygen in the glass network.

Related publications and abstracts

McKeegan R.*, Holycross M., Cottrell E. (2018) “Probing the Earth’s deep oxygen cycle with vanadium: the temperature dependence of partitioning between rutile and silicate melt”, GSA Annual Meeting, Indianapolis IN

Holycross M., Cottrell E. (2018) “A new oxybarometer for rutile”, Goldschmidt conference, Boston MA

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Diffusion geospeedometry

Equilibrium changes in pressure, temperature and composition redistribute cations and their isotopes in the solid Earth. However, the extent of chemical exchange in response to shifting conditions will be limited by diffusion, which controls the transportation of elements in geologic materials over the nanometer-to-meter scale. I calibrate diffusion coefficients in the lab to understand how kinetic phenomena preserved in natural samples record the tempos of heating, alteration and exhumation events in magmatic and metamorphic systems. Shown above is an RGB cathodoluminescence (CL) image of a grain boundary diffusion experiment. The blue color is from the presence of titanium, a CL activator, in the region adjacent to the crystalline grain boundaries.

Related publications and abstracts

Holycross M., Watson E.B. (2018) “Li diffusion in plagioclase: a geospeedometer for rapid heating events”, GSA Annual Meeting, Indianapolis IN

Holycross M.E., Watson E.B. (2018) Trace element diffusion and kinetic fractionation in wet rhyolitic melt, Geochimica et Cosmochimica Acta 232: 14-29

Holycross M.E., Watson E.B., Richter F., Villeneuve J. (2018) Diffusive fractionation of Li in wet, highly silicic melts, Geochemical Perspectives Letters 6: 39-42

Holycross M.E., Watson E.B. (2016) Diffusive fractionation of trace elements in basaltic melt, Contributions to Mineralogy and Petrology 171: 1-15

Watson E.B., Cherniak D.J., Holycross M.E. (2015) Diffusion of phosphorus in olivine and molten basalt, American Mineralogist 100: 2053-2065