Volatile abundances in submarine glasses from the North Fiji and Lau back-arc basins

Abstract

Glasses from submarine lavas of the North Fiji and Lau back-arc basins were analyzed by high-temperature mass spectrometry for volatiles. Abundances for H 2O, Cl, F,S and CO 2 in glasses ranging in composition from depleted, primitive MORB to enriched, transitional tholeiites are reported. The samples divide into three groups based on K 2O vs. H 2O, Ba/Zr vs. H 2O and K 2O/H 2O vs. P 2O 5/H 2O variation diagrams. At similar Mg#, the least evolved samples studied are nearly identical to N-type MORB in H 2O abundances but show Cl contents enriched by a factor of 5. More enriched samples, classified as back-arc basin basalts (BABB) on the basis of major/trace elements and isotopes, are not as hydrous (at similar Mg#) as those from the Mariana and East Scotia Sea back-arc basins. The data indicate that not all back-arc basins erupt lavas with the distinct volatile and other elemental characteristics of lavas from the Mariana Trough and Scotia Sea.