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The modern volcanoes of Indonesia, represent the cycling of material and heat along the Southeast (SE) Asian subduction zone. This volcanic activity is well exemplified in the middle section of Java Island, which is found on the Sunda arc portion of the SE Asian convergent system. Central Java's volcanoes inherit their geochemistry from silicate melts that formed due to hydrous melting at a range of depths above their subducting slab: ∼136 to ∼272 km. It has been shown that across-arc variations in magmatic trace elements like boron (B) can shed light on the quantity and type of slab-derived fluid released in a forearc to back-arc sequence. In this study, we present major, trace and radiogenic chemistry data for five volcanoes arranged in a roughly N-S lineament across Central Java. We show that the observed chemical changes across the section of the Sunda arc can be explained by variations in different kinds of source from fluid mobile material being devolatilized across the arc. Our mixing models suggest that the magmas underlying these volcanoes see a decreasing ratio of sediment to altered oceanic crust (AOC) contributions from the volcanic front (Merapi volcano) toward the rear-arc (Muria). We estimate that a maximum ∼1% contribution of sediment-derived fluid is sufficient to explain the chemical systematics of this arc segment. Shallow slab dehydration, mostly from the sediment cover, at low temperature (at <60 km of slab depth) transfers the fluid high in B/Nb, Ba/Nb, 87Sr/86Sr and 207Pb/204Pb to the mantle beneath this region's arc front, inducing flux melting. Farther from the trench, the signature of the subducting oceanic plate increases and peaks at around ∼160–170 km of slab depth, carrying substantial slab liquids with moderate to low B/Nb and Ba/Nb with lower 87Sr/86Sr and 207Pb/204Pb to the mantle beneath middle- and rear-arc region. Beyond 200 km, in the rear-arc, evidence for slab liquid is low, but not non-existent. Unexplained Ba-enrichment in magmas from across the arc may account for the role of subduction serpentinite dehydration in the subduction channel or local crustal assimilation. This study provides a conceptual model for material transfer from the subducting slab in SE Asia. Our findings have important implications for the understanding of geochemical cycling in this region, as well as the impact of these cycles on present and past volcanism. • Slab liquid with different proportion of SED/AOC is evident across Central Java, high at arc front and low at the rear-arc • Shallow slab liquid is high in FME, 87Sr/86Sr, 207Pb/204Pb; deep slab liquid has moderate/low levels of those components • Elevated Ba/Nb across the arc magmas may hint to the importance of subducting serpentinite in subduction channel [ABSTRACT FROM AUTHOR]