Variable slab material transport mechanisms in Mariana subduction zone

Arc volcanic rocks preserve critical records of subduction zone mass transfer processes, with mélange melting and mantle metasomatism being two potential mechanisms, yet distinguishing them remains challenging. Here, we integrated elemental and Mg-Sr-Nd isotopic data for Mariana arc and back-arc basin basalts to constrain slab material transport mechanisms. Using high-MgO primitive basalts to circumvent the effects of crystal fractionation, we show that both initial arc rifting and arc volcanoes exhibit systematically higher δ26Mg values than mid-ocean-ridge basalt (MORB), consistent with serpentinite-bearing mélange melting. Back-arc basin basalts show MORB-like δ26Mg values, reflecting slab-derived hydrous melt metasomatism of the mantle wedge. These results suggest an evolution in subducted slab component transfer mechanisms from mélange diapirism beneath the arc/initial rift to mantle metasomatism beneath the back arc. This dual-mode transfer framework provides new constraints on the dynamic interplay between slab dehydration and mantle hybridization, offering a refined perspective on material recycling at convergent margins.