Water and the Oxidation State of Subduction Zone Magmas
By Katherine A. Kelley, E. Cottrell. Science, 2009
817 citations recorded by the source corpus.
Tracing Mantle Oxidation The chemical composition of the Earth's mantle varies with tectonic setting. For example, basaltic melts near subduction zones are more oxidized than magma near divergent plate boundaries. Kelley and Cottrell (p. 605; see the Perspective by Hirschmann) examined melts formed in different tectonic environments, using highly sensitive synchrotron-based analytical methods. The oxidation state of Fe increased with water content and mobile trace elements concentrations. Thus, fluids released from wet subducting plates drive mantle oxidation above subduction zones, which may help to explain the spatial differences in oxygen fugacity of the mantle. Oxidation of Earth’s mantle at subduction zones is caused by fluids released from the melting of subducting plates. Mantle oxygen fugacity exerts a primary control on mass exchange between Earth’s surface and interior at subduction zones, but the major factors controlling mantle oxygen fugacity (such as volatiles and phase assemblages) and how tectonic cycles drive its secular evolution are still debated. We present integrated measurements of redox-sensitive ratios of oxidized iron to total iron (Fe3+/ΣFe), determined with Fe K-edge micro–x-ray absorption near-edge structure spectroscopy, and pre-eruptive magmatic H2O contents of a global sampling of primitive undegassed basaltic glasses and melt inclusions covering a range of plate tectonic settings. Magmatic Fe3+/ΣFe ratios increase toward subduction zones (at ridges, 0.13 to 0.17; at back arcs, 0.15 to 0.19; and at arcs, 0.18 to 0.32) and correlate linearly with H2O content and element tracers of slab-derived fluids. These observations indicate a direct link between mass transfer from the subducted plate and oxidation of the mantle wedge.
Subfields: Geophysics
View Paper: https://www.semanticscholar.org/paper/9711e2993d012e1ec59a87407e6414082c6ebc73
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Citations in the corpus
- The Role of Water in Generating the Calc-alkaline Trend: New Volatile Data for Aleutian Magmas and a New Tholeiitic Index (2010, methodology): “Micro-mXANES (X-ray absorption near edge structure) analysis of one MI yields 30% Fe3þ/ Fe (Kelley & Cottrell, 2009), consistent with FMQ þ2·1 [using Fe3þ/ Fe and the relationship given by Kress & Carmichael (1991)].”
- Origin and evolution of the atmospheres of early Venus, Earth and Mars (2018, background): “N2 degassing would have followed once subduction zones began injecting oxidants, like Fe+3 or S + 6 into the mantle (Kelley and Cottrell 2009).”
- A hydrogen-based oxidation mechanism relevant to planetary formation (2013, background): “The Earth’s mantle must have had a low oxygen fugacity after the Giant Impact event responsible for creation of our Earth–Moon binary planet system (Canil et al., 1994; Frost et al., 2008; Frost and McCammon, 2008; Kelley and Cottrell, 2009).”
- Crystallization of oxidized, moderately hydrous arc basalt at mid- to lower-crustal pressures: implications for andesite genesis (2012, neutral): “The basaltic starting material was prepared with 2 wt% H2O, near the lower limit of common arc basaltic melt inclusions (Métrich and Wallace 2008; Kelley and Cottrell 2009), but at the high end of dissolved H2O values for back-arc basin basalts (Stolper and Newman 1994).”