VIRTUAL
POSTER SESSION
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Motivation Oxidation-reduction reactions play a major role in mediating the chemical evolution of planets. Despite this importance, the oxidation state of the Earth’s mantle is not well constrained. Water can be a powerful oxidizing agent, and we would like to understand the relationship between Earth’s oxidation state and water cycling on our planet. In contrast to previous research and intuition, a recent study by Lee et al. (2005) has indicated that the mantle beneath wet subduction zones is no more oxidized than beneath dry mid-ocean ridges. We want to investigate this application of water’s oxidizing abilities. This study may also help us to better understand current mantle processes.
We traveled to a synchrotron radiation source at Brookhaven National Lab to analyze our samples using XANES (x-ray absorption near-edge structure) spectroscopy. This data provided us with information about the oxidation state of the iron in our samples. We then used FTIR (Fourier transform infrared) spectroscopy to determine the water content of the melt inclusions.
We offer two possible mechanisms to explain our results: a) that the correlation we discovered is due to water oxidizing the oceanic lithosphere during its transit across the sea floor
b) that water oxidizes the iron in the mantle during the melt
generation process |
Our
samples are olivine-hosted melt inclusions, each about 100 microns
in diameter. We will be studying the iron present in these samples,
as iron is the most abundant multi-valent element in the Earth,
making it a good proxy for oxidation state. Melt inclusions form
in magma chambers during subduction, 6-20 kilometers deep, and
make their way to the Earth’s surface through volcanic eruptions.
They provide a “snapshot” of conditions in the mantle,
revealing its water content and oxidation state. Melt inclusions
preserve volatile content of magma when the magma outside the
olivine degasses. This allows us to study conditions immediately
below arc volcanoes.
The
relationship we found is consistent with water's oxidizing role
in the mantle, supporting the idea that subduction zones are more
oxidized than ridges due to their higher water content. |
Smithsonian
Institution The information presented here, as part of the Research Training Program Virtual Poster Session, represents preliminary data as the result of ten-weeks of investigation in-residence at the National Museum of Natural History. This is not an official publication nor are the finding presented here necessarily conclusive or definitive. As preliminary information, these results and/or findings should not be cited as part of conclusive work. Please contact the author if you would like further information about this research as well as the resulting scientific publication and/or presentation. |