Ironing Out the Oxidation of Earth's Mantle

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Science  31 Jul 2009:
Vol. 325, Issue 5940, pp. 545-546
DOI: 10.1126/science.1176882

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Lavas from island arc volcanoes form when the crust is recycled into the mantle at subduction zones (see the figure). These lavas are more oxidized than those produced at mid-ocean ridge volcanoes. On page 605 of this issue, Kelley and Cottrell (1) use a high–spatial resolution method to determine iron oxidation states of glasses from a suite of volcanic rocks, including a broad sampling of tiny inclusions trapped in minerals from arc volcanoes that have not undergone degassing. They correlate these measurements with dissolved water and trace element concentrations determined by other microanalytical techniques, and link the oxidation of arc volcano magmas with oxidants in the fluids that infiltrate the mantle wedge above subduction zones, as opposed to other processes, such as volcanic degassing in surface regions.