RELAMINATION AND THE DIFFERENTIATION OF CONTINENTAL CRUST

Sediment subduction, subduction erosion, arc subduction, and continent subduction may all contribute to the differentiation of continental crust. Subducted mafic rocks become eclogite, whereas more silica-rich rocks transform into felsic gneisses. The mafic rocks are gravitationally unstable and may sink into the mantle, whereas the more-felsic rocks rise buoyantly through the mantle, undergo melting and melt extraction, and are relaminated to the base of the crust. These processes may be more efficient than lower crustal foundering at generating large volumes of material with the major- and trace-element composition of continental crust, and may have operated rapidly enough to have refined the composition of the entire continental crust over the lifetime of Earth. If so, felsic rocks could form much of the lower crust, and the bulk continental crust may be more silica rich than generally considered.