A Composite Diapir Model for Extensive Basaltic Volcanism

Magmas from Subducted Oceanic Crust Entrained within Mantle Plumes

Abstract

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 660km discontinuity drags fragments of subducted oceanic crust stagnating there into the diapir and forms a“composite diapir”. Because of the differential melting between peridotite and oceanic crust, ascent of such a composite diapir can produce voluminous basaltic magma by melting of subducted oceanic crust, capsulated in solid peridotite. Release of the voluminous basalt magma would be triggered by partial melting of diapir-forming peridotite in the shallow upper mantle. Physical and chemical properties of the resulting hybrid magma can explain most features of continental flood basalt.