期刊
SCIENCE
卷 354, 期 6318, 页码 1403-1405出版社
AMER ASSOC ADVANCEMENT SCIENCE
DOI: 10.1126/science.aal1303
关键词
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资金
- Deep Carbon Observatory
- National Science Foundation [EAR1049992]
- European Research Council [307322]
- Division Of Earth Sciences
- Directorate For Geosciences [1049992] Funding Source: National Science Foundation
The redox state of Earth's convecting mantle, masked by the lithospheric plates and basaltic magmatism of plate tectonics, is a key unknown in the evolutionary history of our planet. Here we report that large, exceptional gem diamonds like the Cullinan, Constellation, and Koh-i-Noor carry direct evidence of crystallization from a redox-sensitive metallic liquid phase in the deep mantle. These sublithospheric diamonds contain inclusions of solidified iron-nickel-carbon-sulfur melt, accompanied by a thin fluid layer of methane +/- hydrogen, and sometimes majoritic garnet or former calcium silicate perovskite. The metal-dominated mineral assemblages and reduced volatiles in large gem diamonds indicate formation under metal-saturated conditions. We verify previous predictions that Earth has highly reducing deep mantle regions capable of precipitating a metallic iron phase that contains dissolved carbon and hydrogen.
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