A new concept for the genesis of felsic magma: the separation of slab-derived supercritical liquid

Hajime Taniuchi,Takeshi Kuritani,Eizo Nakamura,Tetsuya Yokoyama,Mitsuhiro Nakagawa

doi:10.1038/s41598-020-65641-6

Hajime Taniuchi, Takeshi Kuritani + Show 3 more

Open Access

https://doi.org/10.1038/s41598-020-65641-6

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Abstract

Felsic magmas produced at subduction zones have played an important role in the generation and evolution of the continental crust. For the origin of felsic magmas, processes such as fractional crystallization of mafic magmas, partial melting of crustal materials, partial melting of subducting slabs, and partial melting of pyroxenitic mantle wedge components have been proposed. Recent experimental studies have predicted that felsic melt can also be produced in the mantle wedge by the separation of slab-derived supercritical liquid beyond depths corresponding to the critical point. To date, however, the presence of felsic magma of this origin has not yet been reported. In this study, we investigated dacitic lavas and preceding calc-alkaline andesite lavas from the Rishiri Volcano, located at the rear of the Kuril arc. We show that hydrous felsic melt and aqueous fluid were separated from slab-derived supercritical liquid in the mantle wedge. The former erupted as dacitic magma whilst the aqueous fluid induced the generation of primary basaltic magma involved in creating calc-alkaline andesite magma. We infer that slab-derived supercritical liquid is an efficient transport medium for moving silicate-rich components from subducting slabs to the Earth’s surface, and that this process may have contributed to the growth of the continental crust.

Highlights

Felsic magmas produced at subduction zones have played an important role in the generation and evolution of the continental crust
Subduction-zone magmatism is considered to have played an important role in the generation and evolution of the continental crust, because the chemical composition of calc-alkaline andesites that are widespread in island arcs and active continental margins is similar to the average composition of the continental crust[1,2]
Some felsic magmas have been emplaced as large granitic plutons, which contribute to the establishment of a buoyant continental crust[5,6], and others have mixed with mafic magmas to produce calc-alkaline andesitic magmas and other intermediate magmas in crustal magma chambers[7], producing geochemical variability in the crust[2]

Summary

Introduction

Felsic magmas produced at subduction zones have played an important role in the generation and evolution of the continental crust. Recent experimental studies have predicted that felsic melt can be produced in the mantle wedge by the separation of slab-derived supercritical liquid beyond depths corresponding to the critical point. We show that hydrous felsic melt and aqueous fluid were separated from slab-derived supercritical liquid in the mantle wedge The former erupted as dacitic magma whilst the aqueous fluid induced the generation of primary basaltic magma involved in creating calc-alkaline andesite magma. It has been suggested that felsic magmas found at subduction-zone volcanoes are produced by mechanisms including fractional crystallization with or without crustal assimilation[8], partial melting of the crust[9,10], and partial melting of metasomatised silica-excess pyroxenite mantle[11,12]. Experimental studies have suggested that intermediate to felsic magma may be produced as hydrous melt through the separation of slab-derived supercritical liquids in the sub-arc mantle. We suggest that the dacitic magmas represent hydrous melts generated through separation of slab-derived supercritical liquid

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