An overview of the volatile systematics of the Lau Basin - Resolving the effects of source variation, magmatic degassingand crustal contamination

Abstract

The Lau Basin erupts lavas with a range of geochemical features reflecting a complex history of interaction involving dif- ferent mantle sources. The Valu Fa Ridge (VFR) and Mangatolu Triple Junction (MTJ) region have lavas with arc-like char- acteristics, Niuafo'ou Island (NV), Peggy Ridge and Central and Eastern Lau Spreading Centers (PR, CLSC and ELSC) erupt mid-ocean ridge basalt (MORB)-like volcanics, whereas the Rochambeau Bank (RB) has features akin to ocean island basalt (OIB). To characterize the volatile systematics of these various regions, we report a comprehensive study of 39 submar- ine lavas from these various eruptive centers encompassing analyses of the noble gases (He, Ne, and Ar) and carbon (CO2) ？both isotopes and abundances ？together with other major volatile phases (H2O, S, Cl, and F). Helium isotope ratios of the NV, MTJ, CLSC, and ELSC are MORB-like for the most part except for differentiated lavas that tend to have lower, more radiogenic 3He/4He values. The RB has considerably higher 3He/4He ratios (up to 23 RA in this work) which extend as far south as the PR. The influence of 'plume-like' sources in the RB is also apparent in Ne isotopes: RB samples follow a trend similar to Hawaiian basalts in 3-isotope neon space. However, RB lavas have lower 40Ar/36Ar (300？730) and higher [36Ar] than CLSC and ELSC, suggesting greater air contamination. e char- acteristics, Niuafo'ou Island (NV), Peggy Ridge and Central and Eastern Lau Spreading Centers (PR, CLSC and ELSC) erupt mid-ocean ridge basalt (MORB)-like volcanics, whereas the Rochambeau Bank (RB) has features akin to ocean island basalt (OIB). To characterize the volatile systematics of these various regions, we report a comprehensive study of 39 submar- ine lavas from these various eruptive centers encompassing analyses of the noble gases (He, Ne, and Ar) and carbon (CO2) ？both isotopes and abundances ？together wit