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PUBLISHED ONLINE: 13 MARCH 2011 | DOI: http://www.nature.com/doifinder/10.1038/ngeo1104
Web End =10.1038/NGEO1104
Explosive eruptions at mid-ocean ridges driven by CO2-rich magmas
Christoph Helo1*, Marc-Antoine Longpr1, Nobumichi Shimizu2, David A. Clague3 and John Stix1
The abundance of volatile compounds, and particularly CO2,
in the upper oceanic mantle affects the style of volcanic eruptions. At mid-ocean ridges, eruptions are generally dominated by the gentle effusion of basaltic lavas with a low volatile content. However explosive volcanism has been documented at some ocean spreading centres13, indicative of abundant volatile compounds. Estimates of the initial CO2 concentration of primary magmas can be used to constrain the CO2 content of the upper oceanic mantle, but these estimates vary greatly4,5. Here we present ion microprobe
measurements of the CO2 content of basaltic melt trapped in plagioclase crystals. The crystals are derived from volcanic ash deposits erupted explosively at Axial Seamount, Juan de Fuca Ridge, in the northeast Pacic Ocean. We report unusually high CO2 concentrations of up to 9,160 ppm, which indicate that the upper oceanic mantle is more enriched in carbon than previously thought. We furthermore suggest that CO2 uxes along mid-ocean ridges4,5 vary signicantly. Our results demonstrate that elevated uxes of CO2 from the upper oceanic mantle can drive explosive eruptions at mid-ocean ridges.
Mid-ocean ridges (MORs) are the most active and voluminous volcanic systems on Earth, forming nearly 60% of the Earths crust. Owing to its large volume, MOR volcanism is a key contributor to the total CO2 flux from the mantle to the Earths surface. Recent work has documented the widespread existence of volcaniclastic ash deposits comprising basaltic glass fragments at MOR sites13. Although widely interpreted as primary products of submarine explosive eruptions1,2,6, some researchers argue for lavaseawater interaction7,8. Owing to its low solubility, CO2 is the only magmatic volatile phase undergoing significant exsolution as basaltic magma ascends to the sea floor9, hence the only volatile that can drive explosive eruptions at these depths. Pyroclastic activity in MOR environments therefore is controlled by the primary CO2 content of basaltic liquids, and consequently by the carbon budget of the mantle source. Initial CO2 contents of variously enriched basalts from the Mid-Atlantic Ridge, including so-called popping rock, are inferred to be between 660 and 57,600 ppm, on the basis...