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Segregating gas from melt: an experimental study of the Ostwald ripening of vapor bubbles in magmas
Diffusive coarsening (Ostwald ripening) of H 2 O and H 2 O-CO 2 bubbles in rhyolite and basaltic andesite melts was studied with elevated temperature–pressure experiments to investigate the rates and time spans over which vapor bubbles may enlarge and attain sufficient buoyancy to segregate in magma...
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Published in: | Contributions to mineralogy and petrology 2011-02, Vol.161 (2), p.331-347 |
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Main Authors: | , , , |
Format: | Article |
Language: | English |
Subjects: | |
Citations: | Items that this one cites Items that cite this one |
Online Access: | Get full text |
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Summary: | Diffusive coarsening (Ostwald ripening) of H
2
O and H
2
O-CO
2
bubbles in rhyolite and basaltic andesite melts was studied with elevated temperature–pressure experiments to investigate the rates and time spans over which vapor bubbles may enlarge and attain sufficient buoyancy to segregate in magmatic systems. Bubble growth and segregation are also considered in terms of classical steady-state and transient (non-steady-state) ripening theory. Experimental results are consistent with diffusive coarsening as the dominant mechanism of bubble growth. Ripening is faster in experiments saturated with pure H
2
O than in those with a CO
2
-rich mixed vapor probably due to faster diffusion of H
2
O than CO
2
through the melt. None of the experimental series followed the time
1/3
increase in mean bubble radius and time
−1
decrease in bubble number density predicted by classical steady-state ripening theory. Instead, products are interpreted as resulting from transient regime ripening. Application of transient regime theory suggests that bubbly magmas may require from days to 100 years to reach steady-state ripening conditions. Experimental results, as well as theory for steady-state ripening of bubbles that are immobile or undergoing buoyant ascent, indicate that diffusive coarsening efficiently eliminates micron-sized bubbles and would produce mm-sized bubbles in 10
2
–10
4
years in crustal magma bodies. Once bubbles attain mm-sizes, their calculated ascent rates are sufficient that they could transit multiple kilometers over hundreds to thousands of years through mafic and silicic melt, respectively. These results show that diffusive coarsening can facilitate transfer of volatiles through, and from, magmatic systems by creating bubbles sufficiently large for rapid ascent. |
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ISSN: | 0010-7999 1432-0967 |
DOI: | 10.1007/s00410-010-0535-x |