Experimental evidence for the existence of iron-rich metal in the Earth's lower mantle

Details Experimental evidence for the existence of iron-rich metal in the Earth's lower mantle Experimental evidence for the existence of iron-rich metal in the Earth's lower mantle

Mar 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004natur.428..409f&link_type=abstract

Nature, Volume 428, Issue 6981, pp. 409-412 (2004).

Physics

77

Scientific paper

The oxidation state recorded by rocks from the Earth's upper mantle can be calculated from measurements of the distribution of Fe3+ and Fe2+ between the constituent minerals. The capacity for minerals to incorporate Fe3+ may also be a significant factor controlling the oxidation state of the mantle, and high-pressure experimental measurements of this property might provide important insights into the redox state of the more inaccessible deeper mantle. Here we show experimentally that the Fe3+ content of aluminous silicate perovskite, the dominant lower-mantle mineral, is independent of oxygen fugacity. High levels of Fe3+ are present in perovskite even when it is in chemical equilibrium with metallic iron. Silicate perovskite in the lower mantle will, therefore, have an Fe3+/total Fe ratio of at least 0.6, resulting in a whole-rock ratio of over ten times that of the upper mantle. Consequently, the lower mantle must either be enriched in Fe3+ or Fe3+ must form by the disproportionation of Fe2+ to produce Fe3+ plus iron metal. We argue that the lower mantle contains approximately 1wt% of a metallic iron-rich alloy. The mantle's oxidation state and siderophile element budget have probably been influenced by the presence of this alloy.

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