Infrared Spectroscopic Measurements of CO\u3csub\u3e2\u3c/sub\u3e and H\u3csub\u3e2\u3c/sub\u3eO in Juan de Fuca Ridge Basaltic Glasses

Dissolved H2O and CO2 contents in basaltic glasses from the Juan de Fuca Ridge and neighboring seamounts were determined by infrared spectroscopy. CO2 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 CO2 contents that we interpret to be the result of variable amounts of degassing. The lowest CO2 contents at each depth are in reasonable agreement with the experimentally determined CO2 solubility curve for basalt at low pressures. All glasses with CO2 values higher than the experimentally determined solubility at the eruption depth are oversaturated because of incomplete degassing. The highest CO2 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 CO2 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. H2O 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)