科研之友
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摘要
The creation of ocean crust by lava eruptions is a fundamental Earth process, involving immediate and immense transfers of heat and chemicals from crust to ocean. This transfer creates event plumes ("megaplumes"), massive ellipsoidal eddies with distinctive and consistent chemical signatures. Here we report the discovery of unique event plumes associated with a 2008 eruption on the Northeast Lau Spreading Center. Instead of a large plume hundreds of meters thick, we detected at least eight individual plumes, each similar to 50 m thick and apparently only 1-3 km in diameter, yet still rising 200-1000 m above the eruption site. Low and uniform (3)He/heat (0.041 x 10(-17) mol/J) and dissolved Mn/heat (0.04 nmol/J) ratios in water samples were diagnostic of event plumes. High H(2) concentrations (up to 9123 nM) and basalt shards confirmed extensive interactions between molten lava and event plume source fluids. Remote vehicle observations in 2009 mapped a new, small (1.5-5.8 x 10(6) m(3)) lava flow. Our results suggest that event plumes are more variable, and thus perhaps more common, than previously recognized. Small event plumes may be preferentially associated with small or sheet-flow eruptions, and massive event plumes with slowly extruding pillow mounds 25-75 m thick. Despite this correlation, and high H(2) concentrations, existing theory and seafloor observations argue that cooling lava cannot transfer heat fast enough to create the buoyancy flux required for event plumes. The creation of event plumes under a broad range of eruption conditions provides new constraints for any theory of their formation. Components: 12,000 words, 12 figures, 2 tables.
- 出版日期2011-9-16
