Origins of ultramafic rocks in the Sulu Ultrahigh-pressure Terrane, Eastern China

► We show mineral and bulk compositions of ultramafic rocks from the Sulu UHP belt. ► The protoliths of serpentinites are mantle peridotites below the margin of the NCC. ► The peridotites are highly refractory even compared to ancient SCLM below the NCC. ► They underwent extensive flux melting during the subduction of the Tethyan Sea. ► Buoyant gneiss allowed the exhumation of the peridotites in the subduction channel.