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DTSTART;VALUE=DATE:20200528
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DTSTAMP:20260718T134040
CREATED:20200512T030817Z
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UID:310-1590624000-1590710399@xrayabsorption.org
SUMMARY:Megan Holycross:	Probing the deep Earth oxygen cycle with XANES
DESCRIPTION:The oxidation state of the solid Earth influences\, to a first order\, the structure of the planet and the chemistry of rocks\, ores and volcanic gases; mass transfer of oxygen between terrestrial reservoirs enables a habitable world. Fe K-edge XANES spectroscopy shows magmas erupted from continental crust\, formed at subduction zones\, are more oxidized than magmas erupted from oceanic crust\, formed at mid-ocean ridges (e.g.\, Kelley and Cottrell 2009; Science). However\, there is long-standing debate over the timing and mechanism of the processes that produce oxidized continental crust. The high-pressure mineral phase garnet is a key reservoir of iron in the crust and garnet Fe3+/ƩFe ratios record the transfer of oxygen throughout the subduction process. Here\, I’ll use garnet Fe-XANES to quantify the oxidation state of two suites of subduction-related rocks to examine changes in the deep Earth oxygen cycle over space (scale of ~100 km) and time (scale of ~2.5 billion years). \nReferences: \n\n\n\nK. A.  Kelley and E. Cottrell\, Water and the Oxidation State of Subduction Zone Magmas Science  325\, pp 605  (2009)   https://doi.org/10.1126/science.1174156 \n\n\nM. D. Dyar\, et al\,  Accurate determination of ferric iron in garnets by bulk Mössbauer spectroscopy and synchrotron micro-XAS American Mineralogist 97 pp 1726–1740 (2012) https://doi.org/10.2138/am.2012.4107\n\n  \n  \n 
URL:https://xrayabsorption.org/events/journalclub-megan-holycross/
CATEGORIES:XAFS Journal Club
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