A COMPOSITE DIAPIR MODEL FOR EXTENSIVE BASALTIC VOLCANISM - MAGMAS FROM SUBDUCTED OCEANIC-CRUST ENTRAINED WITHIN MANTLE PLUMES

A composite diapir model for extensive basaltic volcanism is Proposed on the basis of the melting phase relations of subducted oceanic crust in the mantle. Ascending peridotitic diapir across 660 km discontinui ty drags fragments of subducted oceanic crust stagnating there into th e diapir and forms a ''composite diapir''. Because of the differential melting between peridotite and oceanic crust, ascent of such a compos ite diapir can produce voluminous basaltic magma by melting of subduct ed oceanic crust, capsulated in solid peridotite. Release of the volum inous basalt magma would be triggered by partial melting of diapir-for ming peridotite in the shallow upper mantle, Physical and chemical pro perties of the resulting hybrid magma can explain most features of con tinental flood basalt.