DEGASSING OF SUBMARINE LAVAS ON THE COAXIAL SEGMENT OF THE JUAN DE FUCA MID-OCEAN RIDGE

When lavas are erupted in the submarine environment, they are often times oversaturated with dissolved volatiles. As the lava flows, the volatiles are lost into the seawater. If the lava has sufficient time to cool, the degassing process will continue until an equilibrium concentration is reached. However, if the lava cools quickly the resulting glass and rocks will retain their oversaturated concentration of the volatiles. This study involves glass samples from two well mapped eruption events on the Coaxial Segment of the Juan de Fuca Mid-Ocean Ridge. By measuring the concentrations of H2O and CO3 in the samples, this study attempted to verify the hypothesis that in a submarine environment lavas that cool closer to the source of the flow retain an oversaturation of volatiles because they cool very quickly and don't have time to degas and that the further the lava cools from the source of the flow, the closer the volatile concentration will be to equilibrium.

Glass samples that were about 2mm in diameter were selected for analysis. The samples were ground and polished into glass wafers about 150um thick. The samples were then loaded into the FTIR and absorbance spectra were obtained. The concentrations of CO3 and H2O were determined from the thickness of the chips and the absorbance at particular wavelengths using the Beer-Lambert Law. Each separate flow had a distinctive H2O concentration that didn't vary much between samples of the same flow. The CO3 concentrations were more interesting. Most of the samples from the 1993 lava flow were collected relatively close to the source of the flow. All of these samples were found to be oversaturated with CO3. But there was one sample further away from the source of the flow. This sample had a concentration of CO3 just at equilibrium.

That degassing did occur is evident from the CO3 concentration data from the 1993 lava flow. In this flow the samples that were collected close to the lava source were oversaturated with CO3; but the one sample that was collected further away from the lava source had an equilibrium concentration of CO3. Nothing definitive can be said based on one sample; however, further studies concerning the Axial Segment of the Juan de Fuca Mid-Ocean Ridge are currently under way. I hope to finish these studies and present them along with the completed work described above.