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Experimental constraints on the damp peridotite solidus and oceanic mantle potential temperature

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Science  03 Mar 2017:
Vol. 355, Issue 6328, pp. 942-945
DOI: 10.1126/science.aaj2165

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Turning up the mantle temperature

The temperature at which Earth's mantle begins to melt is a long-standing question in geology. Sarafian et al. present a clever set of experiments to determine the impact of small amounts of water on the melting temperature of mantle rock (see the Perspective by Asimow). This allowed them to reinterpret geophysical observations of melting in the mantle and revise estimates of mantle temperature upward. A hotter mantle has a multitude of implications for mantle melting and geodynamic processes.

Science, this issue p. 942; see also p. 908

Abstract

Decompression of hot mantle rock upwelling beneath oceanic spreading centers causes it to exceed the melting point (solidus), producing magmas that ascend to form basaltic crust ~6 to 7 kilometers thick. The oceanic upper mantle contains ~50 to 200 micrograms per gram of water (H2O) dissolved in nominally anhydrous minerals, which—relative to its low concentration—has a disproportionate effect on the solidus that has not been quantified experimentally. Here, we present results from an experimental determination of the peridotite solidus containing known amounts of dissolved hydrogen. Our data reveal that the H2O-undersaturated peridotite solidus is hotter than previously thought. Reconciling geophysical observations of the melting regime beneath the East Pacific Rise with our experimental results requires that existing estimates for the oceanic upper mantle potential temperature be adjusted upward by about 60°C.

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