EarthRef.org Reference Database (ERR) -- Delaney et al. 1978

Mass spectrometric analyses of phenocrysts, containing glass-vapor inclusions quenched in glassy rims of tholeiitic submarine pillow basalts from spreading centers and Hawaii, indicate that water released from the inclusions upon thermal decrepitation is much less than is released from equivalent volumes of the matrix glass enclosing the same phenocrysts. If water released represents water quenched in the two types of glass (inclusion and matrix) at the time of eruption, then the inclusions contained far less water than the magma surrounding the phenocrysts. Such a condition is consistent with a water depleted source mass for the basalts and an influx of water into the melt after inclusion formation but before quenching at the ocean floor. Glass-vapor inclusions within phenocrysts in tholeiitic pillow basalts from the Marianas Interarc Basin released abundant water even though the adjacent matrix glasses contain only 50% more water than Hawaiian matrix glasses. Water contents of matrix glasses from the Marianas pillow rims are very close to experimental saturation values. In contrast, matrix glasses from MORs and Hawaii are distinctly below water saturation. Vesicles in these glasses are most reasonably accounted for by a CO2-dominated vapor phase, because CO2 contents of those basalt glasses closely approximate experimental solubility limits. Glass-vapor inclusions in phenocrysts from the same pillows appear to contain more CO2 than adjacent matrix glasses. implying that a CO2-dominated vapor developed and outgassed prior to eruption and after inclusion formation. Water influx and CO2 degassing combine to make the CO2/(CO2 + H2O) ratio of seafloor basalt glasses a minimum value for the magma source mass. The sulfur content of the inclusion glasses is normally very similar to that of the enclosing matrix glass.

Keywords
abundance; analysis; carbon; crust; data; degassing; distribution;, East Pacific Ocean Islands; fluid inclusions; gases; geochemistry;, glasses; Hawaii; igneous rocks; inclusions; lava; magmas; mantle;, Mariana Islands; mass spectra; Micronesia; mid-ocean ridges;, Oceania; oceanic crust; phenocrysts; pillow lava; plate tectonics;, Polynesia; rims; spectra; spreading centers; sulfur; United, States; volatiles; volcanic glass; volcanic rocks; water, 02, Geochemistry