Fig. 4.

Sketch of a subduction zone displaying the Mg isotopic compositions of the main components involved in arc magmatism. Seafloor alteration produces isotopically heterogeneous marine sediments, altered MORB, and altered abyssal peridotites. Subduction transports these components into the mantle. Fluids released from these components inherit the isotopically heterogeneous Mg, infiltrate the mantle wedge, and modify its Mg isotopic composition by fluid−rock interactions. Partial melting of this isotopically heterogeneous mantle wedge produced the heterogeneous island arc lavas. Data sources are the same as in Fig. 2.