Schematic diagrams of the crust-mantle interaction in a continental subduction channel and the formation of SSC magmatic rocks. (a) The continental crust is subducted to mantle depths of >80 km, contributing incompatible major and trace elements to the SCLM wedge for crustal metasomatism. (b) Partial melting of the ultramafic to mafic metasomes and their underlying UHP crustal rocks yields mafic, intermediate, and felsic melts, respectively, for synexhumation and postcollisional magmatism. The difference in the composition of magmatic rocks is attributed to different extents of melt-peridotite reaction at the slab-mantle interface, where there is a jelly-sandwich structure in which a weak layer composed of metamorphic, anatectic and metasomatic rocks (the jelly) is sandwiched between the overlying mantle wedge and the underlying subducted crustal slab (Zheng et al. 2013).