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Melting in the Earth's deep upper mantle caused by carbon dioxide


The onset of partial melting beneath mid-ocean ridges governs the cycling of highly incompatible elements from the mantle to the crust1, the flux of key volatiles (such as CO2, He and Ar)1,2 and the rheological properties of the upper mantle3. Geophysical observations4,5,6 indicate that melting beneath ridges begins at depths approaching 300 km, but the cause of this melting has remained unclear. Here we determine the solidus of carbonated peridotite from 3 to 10 GPa and demonstrate that melting beneath ridges may occur at depths up to 330 km, producing 0.03–0.3% carbonatite liquid. We argue that these melts promote recrystallization and realignment of the mineral matrix, which may explain the geophysical observations. Extraction of incipient carbonatite melts from deep within the oceanic mantle produces an abundant source of metasomatic fluids and a vast mantle residue depleted in highly incompatible elements and fractionated in key parent-daughter elements. We infer that carbon, helium, argon and highly incompatible heat-producing elements (such as uranium, thorium and potassium) are efficiently scavenged from depths of 200–330 km in the upper mantle.

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Figure 1: Secondary electron images of typical run products, illustrating distinctions between melt-present and melt-absent conditions.
Figure 2: Experimental constraints on the solidus of natural carbonated peridotite.
Figure 3: Melting regime for passive upwelling beneath a mid-ocean ridge.
Figure 4: Carbon storage and speciation along oceanic mantle adiabat.
Figure 5: Effect of removal of carbonatite melt on the concentration of incompatible trace elements in the residue ( CR) relative to the initial source composition ( C0) as a function of bulk partition coefficient Dperidotite/carbonatite.


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We thank A. C. Withers and C. Aubaud for comments on the manuscript, P. Asimow for conversations and N. Smith for help with the piston cylinder experiments. This work is supported by NSF.

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Correspondence to Rajdeep Dasgupta.

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This file contains the Supplementary Methods, Supplementary Figure 1, Supplementary Tables 1–4 and additional references. (PDF 236 kb)

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Dasgupta, R., Hirschmann, M. Melting in the Earth's deep upper mantle caused by carbon dioxide. Nature 440, 659–662 (2006).

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