洪水玄武岩の成因に関する新しいモデル

Proc. Japan Academy, vol.73B, 1997からの引用

A Composite Diapir Model for Extensive Basaltic Volcanism:
Magmas from Subducted Oceanic Crust Entrained within Mantle Plumes

Atsushi YASUDA1 (yasuda@magma.eri.u-tokyo.ac.jp), Toshitsugu Fujii1 (fujii@magma.eri.u-tokyo.ac.jp)
Kei KURITA2
1 Earthq. Res. Inst., Univ. Tokyo, Japan
2 Department of Earth and Planetary Physics, University of Tokyo, Japan

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 660 km 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.

Fig. 1.(a)Melting phase relations of oceanic crust in the mantle. Shaded area is the partial melting zone of oceanic crust. (b)Schematic drawing of the "composite diapir".