A SUBDUCTION ZONE-SPREADING RIDGE TRANSITION SIGNATURE PRESERVED IN RECENT VOLCANIC ACTIVITY IN THE NE LAU BASIN
Using magmatic differentiation models to relate melt composition and Fe isotope fractionation, we find that estimates of parental melt compositions in the northwestern part of the MVF proximal to the NE Lau Spreading Center, particularly Tolu Volcano, have higher Mg#modeled (~0.68 to 0.71) and higher δ56Femodeled (~-0.22 to -0.19‰). To the southeast, parental melt estimates with lower Mg#modeled (~0.64 to 0.67) and lower δ56Femodeled (~-0.27 to -0.20‰) are dominant, particularly in West Mata Volcano. This suggests West Mata-type melts may contain an isotopically light, enriched (lower Mg#) subduction-derived fluid component, while Tolu-type compositions more closely resemble depleted upper mantle. Volcanoes lying between these two bear transitional δ56Fe-Mg# compositions. The general relationship between parental melt Mg# and δ56Fe estimates in the MVF may capture a transition in tectonic style from subduction (enriched, isotopically light compositions) in the southeast to spreading center (depleted, isotopically heavy compositions) in the northwest.