The study presents a comprehensive geochemical dataset for the recent volcanics from the Mariana Islands, providing new insights into the timing and nature of fluxes from the subducting slab. The lavas exhibit typical island arc characteristics, including large negative niobium anomalies and enrichments in alkaline earth elements and lead. Key ratios correlate with significant 238U excesses, ranging from 0.97 to 1.56 (238U/230Th). Geochemical variations are observed between islands, with Guguan lavas showing the largest 238U excesses, Pb/Ce, and Ba/La ratios, while Agrigan lavas have smaller 238U excesses, the least radiogenic 143Nd/144Nd, and the largest negative cerium and niobium anomalies. These variations indicate two discrete slab additions to the subarc mantle. The geochemical features of Agrigan lavas suggest a dominant contribution from subducted sediment, which is not identical to bulk subducted sediment and shows a marked enrichment of Th relative to Nb. This is attributed to melt fractionation of the sediment with residual rutile and the transfer of sedimentary material as a melt phase. For most highly incompatible elements, the sedimentary component dominates the total elemental budgets of the lavas. The characteristics of Guguan lavas are attributed to a slab-derived aqueous fluid phase, with Pb and Sr isotope compositions pointing to the subducted, altered oceanic crust as the source of this fluid. Variable addition of the sedimentary component and near-constant aqueous fluid flux along the arc strike create the compositional trends observed in the Mariana lavas. High field strength element ratios (Ta/Nb and Zr/Nb) of Guguan lavas are higher than those of most mid-ocean ridge basalts, suggesting a highly depleted subarc mantle prior to any slab additions. The 235U/230Th systematics indicate a time lag of >350 kyr between sediment and mantle melting but <30 kyr between slab dehydration and lava eruption, necessitating rapid magma migration rates and suggesting that the aqueous fluid itself may trigger major mantle melting.The study presents a comprehensive geochemical dataset for the recent volcanics from the Mariana Islands, providing new insights into the timing and nature of fluxes from the subducting slab. The lavas exhibit typical island arc characteristics, including large negative niobium anomalies and enrichments in alkaline earth elements and lead. Key ratios correlate with significant 238U excesses, ranging from 0.97 to 1.56 (238U/230Th). Geochemical variations are observed between islands, with Guguan lavas showing the largest 238U excesses, Pb/Ce, and Ba/La ratios, while Agrigan lavas have smaller 238U excesses, the least radiogenic 143Nd/144Nd, and the largest negative cerium and niobium anomalies. These variations indicate two discrete slab additions to the subarc mantle. The geochemical features of Agrigan lavas suggest a dominant contribution from subducted sediment, which is not identical to bulk subducted sediment and shows a marked enrichment of Th relative to Nb. This is attributed to melt fractionation of the sediment with residual rutile and the transfer of sedimentary material as a melt phase. For most highly incompatible elements, the sedimentary component dominates the total elemental budgets of the lavas. The characteristics of Guguan lavas are attributed to a slab-derived aqueous fluid phase, with Pb and Sr isotope compositions pointing to the subducted, altered oceanic crust as the source of this fluid. Variable addition of the sedimentary component and near-constant aqueous fluid flux along the arc strike create the compositional trends observed in the Mariana lavas. High field strength element ratios (Ta/Nb and Zr/Nb) of Guguan lavas are higher than those of most mid-ocean ridge basalts, suggesting a highly depleted subarc mantle prior to any slab additions. The 235U/230Th systematics indicate a time lag of >350 kyr between sediment and mantle melting but <30 kyr between slab dehydration and lava eruption, necessitating rapid magma migration rates and suggesting that the aqueous fluid itself may trigger major mantle melting.