High-temperature and high-pressure experiments reveal the melting behavior of serpentinites in subduction zone and the genesis of high-Mg magmas

Recent studies have identified serpentinite components in arc magmas, suggesting that subducted serpentinites contribute not only fluids to the mantle wedge but also participate in arc magma formation through partial melting. However, the melting behavior of serpentinites in the mantle wedge and their role in the material cycle of subduction zones remain underexplored. We selected three types of serpentinites: natural serpentinites altered from harzburgite (SE2) and lherzolite (SE3), and synthetic serpentinite (SEQ) containing talc. Experiments were conducted under 700～1300℃ and 4 GPa, to constrain the melting temperature of serpentinites and analyze the composition of the melts. Results show that the solidi among different serpentinite types vary greatly from each other. The solidi of SE3, SEQ, and SE2 are between 900～960℃, 960～1100℃, and 1150～1200℃, respectively. These solidi are higher than the surface temperatures of subducting slab, thus requiring serpentinites diapir into the mantle wedge to melt. Therefore, SE2 and SEQ serpentinites can melt at the bottom of the mantle wedge under relatively lower temperature conditions (960～1100℃), producing komatiitic magmas, whereas in the overlying mantle wedge, SE2 serpentinite undergo more extensive and higher degrees of partial melting at higher temperature conditions (＞1200℃), generating boninitic magmas.