Carbon content and degassing history of the lunar volcanic glasses

• Published in: Nature geoscience Vol. 8; no. 10; pp. 755 - 758
• Main Authors: Wetzel, Diane T., Hauri, Erik H., Saal, Alberto E., Rutherford, Malcolm J.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01-10-2015; Nature Publishing Group
• Subjects: 704/445/209; 704/445/598; 704/445/845; Carbon; Chlorine; Degassing; Earth Sciences; Earth System Sciences; Geochemistry; Geology; Geophysics/Geodesy; Hydrogen isotopes; letter; Moon; Upper mantle; Volcanic eruptions; Water content
• ISSN: 1752-0894; 1752-0908
• DOI: 10.1038/ngeo2511

The volatile-rich eruptions required to produce the lunar volcanic glasses are at odds with a volatile-poor Moon. Analyses of the glasses suggest that there was enough of the volatile element carbon in the parent magmas to drive the eruptions.
Volcanic glasses observed on the lunar surface have been interpreted as the products of volatile-rich, fire-fountain eruptions. Revised estimates of the water content of primitive lunar magmas have overturned the notion of a volatile-poor Moon
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, but degassing of water-rich vapour during volcanic eruptions is inconsistent with geochemical and petrological observations
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. Although degassing of carbon is compatible with observations, the amount of indigenous carbon in lunar volcanic materials is not well constrained. Here we present high-precision measurements of indigenous carbon contents in primitive lunar volcanic glasses and melt inclusions. From our measurements, in combination with solubility and degassing model calculations, we suggest that carbon degassed before water in lunar magmas, and that the amount of carbon in the lunar lavas was sufficient to trigger fire-fountain eruptions at the lunar surface. We estimate—after correcting for bubble formation in the melt inclusions—that the primitive carbon contents and hydrogen/carbon ratios of lunar magmas fall within the range found in melts from Earth’s depleted upper mantle
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. Our findings are also consistent with measurements of hydrogen, fluorine, sulphur and chlorine contents, as well as carbon and hydrogen isotopes, in primitive lunar magmas
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, suggesting a common origin for the volatile elements in the interiors of the Earth and Moon.