Geochemistry of volcanic glasses from the Louisville Seamount Trail (IODP Expedition 330): Implications for eruption environments and mantle melting

Volcanic glasses recovered from four guyots during drilling along the Louisville Seamount Trail, southwest Pacific, have been analyzed for major, trace, and volatile elements (H 2 O, CO 2 , S, and Cl), and oxygen isotopes. Compared to other oceanic island settings, they are geochemically homogeneous, providing no evidence of the tholeiitic stage that characterizes Hawai'i. The degrees and depth of partial melting remained constant over 1–3 Ma represented by the drill holes, and along‐chain over several million years. The only exception is Hadar Guyot with compositions that suggest small degree preferential melting of an enriched source, possibly because it erupted on the oldest and thickest lithosphere. Incompatible element enriched glass from late‐stage volcaniclastics implies lower degrees of melting as the volcanoes moved off the melting anomaly. Volcaniclastic glasses from throughout the igneous basement are degassed suggesting generation during shallow submarine eruptions (<20 mbsl) or as subaerial flows entered the sea. Drill depths may no longer reflect relative age due to postquench downslope movement. Higher volatile contents in late‐stage volcaniclastics indicate submarine eruptions at 118–258 mbsl and subsidence of the edifices below sea level by the time they erupted, or generation in flank eruptions. Glass from intrusion margins suggests emplacement ∼100 m below the surface. The required uplift to achieve these paleo‐quench depths and the subsequent subsidence to reach their current depths exceeds that expected for normal oceanic lithosphere, consistent with the Louisville melting anomaly being <100°C hotter than normal asthenosphere at 50–70 Ma when the guyots were erupted.