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Water and hydrogen are immiscible in Earth’s mantle



In the deep, chemically reducing parts of Earth’s mantle1, hydrous fluids contain significant amounts of molecular hydrogen (H2). Thermodynamic models of fluids in Earth’s mantle so far have always assumed that molecular hydrogen and water are completely miscible. Here we show experimental evidence that water and hydrogen can coexist as two separate, immiscible phases. Immiscibility between water and hydrogen may be the cause of the formation of enigmatic, ultra-reducing domains in the mantle that contain moissanite (SiC) and other phases indicative of extremely reducing conditions2,3. Moreover, the immiscibility between water and hydrogen may provide a mechanism for the rapid oxidation of Earth’s upper mantle immediately following core formation4.

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Figure 1: Synthetic fluid inclusions in olivine formed at 1,000 °C and 2.6 GPa at Fe–FeO buffer conditions.
Figure 2: Synthetic fluid inclusions in olivine formed at 950 °C and 2.3 GPa at Fe–FeO buffer conditions.
Figure 3: Experimental data on the location of the critical curve in the H 2 –H 2 O system.

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We thank H. Schulze for help in sample preparation. This Letter has been improved by comments from D. Walker.

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Authors and Affiliations



E.B. carried out all experiments reported in this Letter. A.A. assisted in the design and interpretation of the experiments. H.K. helped in measuring the Raman spectra and in the geological application of the data. The authors wrote the manuscript together.

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Correspondence to Enikő Bali.

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The authors declare no competing financial interests.

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Supplementary Information

This file contains Supplementary Text and Data showing the model calculation on percolation of hydrogen-rich fluids through the mantle; Supplementary Figures 1-4, which are photographs of run products for the demonstration of immiscibility and complete miscibility between H2 and H2O as observed in our experimental run products and additional references. (PDF 4830 kb)

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Bali, E., Audétat, A. & Keppler, H. Water and hydrogen are immiscible in Earth’s mantle. Nature 495, 220–222 (2013).

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