The release of fluids from subducting slabs is considered to result in partial melting of the mantle wedge and arc magmatism. By contrast, we propose that the breakdown of serpentinites, which acted as a sink for water and fluid-soluble elements released from underlying slab in the mantle wedge, most likely leads to arc magmatism at volcanic fronts. Serpentinites exhumed from mantle wedges in Himalayas, Cuba, and the Alps are enriched in elements that are fluid soluble at low temperatures, such as As, Sb, and Sr. The downward movement of the serpentinite layer by mantle flow transports these elements to deeper, hotter levels in the mantle. Eventual dehydration of serpentinite discharges water and fluid-soluble elements, leading to partial melting of the overlying mantle wedge, thus accounting for the observed enrichment of these elements in magmas at the volcanic front.

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