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Published September 1988 | public
Journal Article

Infrared spectroscopic measurements of CO_2 and H_2O in Juan de Fuca Ridge basaltic glasses


Dissolved H_2O and CO_2 contents in basaltic glasses from the Juan de Fuca Ridge and neighboring seamounts were determined by infrared spectroscopy. CO_2 contents range from about 45 to 360 ppm by weight, with carbonate ion complexes the only detectable form of dissolved carbon. Samples erupted at a given depth exhibit a large range in dissolved CO_2 contents that we interpret to be the result of variable amounts of degassing. The lowest CO_2 contents at each depth are in reasonable agreement with the experimentally determined CO_2 solubility curve for basalt at low pressures. All glasses with CO_2 values higher than the experimentally determined solubility at the eruption depth are oversaturated because of incomplete degassing. The highest CO_2 contents are spatially associated with the local topographic highs for each ridge segment. Lavas from relatively deep areas may have had greater opportunity to degas during ascent from a magma chamber or during lateral flow in dikes or seafloor lava flows. The highest observed CO_2 concentrations are from the axial seamount and lead to an estimate of a minimum depth to the magma chamber of 2.7 km beneath the ridge axis. H_2O contents vary from 0.07 to 0.48 wt.%, with hydroxyl groups the only detectable form of dissolved water. Water contents correlate positively with FeO^*/MgO and the highest water contents are found in the incompatible element-enriched Endeavour segment lavas. Variations in ratios of water to other incompatible elements suggest that water has a bulk partition coefficient similar to La during partial melting (D ∼ 0.01).

Additional Information

© 1988 Elsevier Science Publishers. Received 12 January 1988. Revised 13 June 1988. We thank P. Rosener for assistance in infrared spectroscopic analyses and D. Burnett for assistance in the vesicle content determinations. C. Langmuir encouraged us to delve into controls of water content variations, though he is not responsible for our interpretations. J. Blank generously shared her data with us and discussed aspects of her work on the same samples. We also thank T. Plank and C. Langmuir for calculating the liquidus temperature of TT152-13. We are grateful to J. Moore and C. Langmuir for their thoughtful reviews. The research at Caltech was performed under NSF grants EAR-8417434 and EAR-8618229 (E.M.S.). Samples were collected with support of NSF grants OCE79-25041, OCE81- 11413, and OCE83-09812 (J.R.D.). Caltech Division of Geological and Planetary Science Contribution Number 4573.

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