Native Iron in the Continental Lower Crust: Petrological and Geophysical Implications

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Science  16 Aug 1985:
Vol. 229, Issue 4714, pp. 647-649
DOI: 10.1126/science.229.4714.647


Lower crustal granulite xenoliths recovered from a kimberlite pipe in western Africa contain native iron (Fe0) as a decomposition product of garnet and ilmenite. Magnetic measurements show that less than 0.1 percent (by volume) of iron metal is present. Data from geothermometry and oxygen geobarometry indicate that the oxide and metal phases equilibrated between iron-wüstite and magnetite-wüstite buffers, which may represent the oxidation state of the continental lower crust, and the depleted lithospheric upper mantle. Ferromagnetic native iron could be stable to a depth of ≃ 95 kilometers and should be considered in the interpretation of long-wavelength static magnetic anomalies.