Features of heat and mass transfer processes under the Avachinsky volcano (Kamchatka)

We investigated the processes beneath the Avacha volcano using mantle peridotite xenoliths  the with the EPMA, electronic microscope and ICP methods and  numeric modeling of the mass transfer accounting the melt fluid reactions with peridotites

The decompression melting processes  in peridotites beneath Avachinsky volcano (Kamchatka) are associated with seismic events. After the reactions with the Si, Ca, Na, K  from partial  melts associated  with  the  subduction related fluids the spinel and orthopyroxene were melted and essentially clinopyroxene veins were formed. Secondary crystals growth in the mantle xenoliths (with melt and fluid inclusions) are associated possibly with  the fluids appeared  due to retrograde boiling of the magma chamber beneath the volcano.

The processes of sublimation and recrystallization of  Avacha harzburgites was investigated at the facility in the Institute of  Nuclear Physics (Novosibirsk, Russia), which generates high-density electron beams and makes it possible to obtain boiling ultrabasic and basic liquids and condensates of magmatic gas on the surface of  harzburgite.

Results of  experiments provides a satisfactory explanation for the observed local heterophase alterations within ultramafic rocks that have experienced multistage deformation beneath volcanoes of the Kamchatka volcanic front.

Mathematical model of convective heating and metasomatic reactions in harzburgites were modeled using the  Selector PC thermodynamic software. The obtained virtual dynamic patterns of metasomatic zoning across the mantle wedge show   how   composition   variations   of   fluids   and  PT  conditions   at   their   sources   influence   the   facies   of   metasomatized   mantle   wedge harzburgite.   Such processes are apparently common to seismically  deformed   permeable   lithosphere   above   magma   reservoirs.  

There are two regions fluid filtration conditions under the Avachinsky volcano which are regulated by the tectonic conditions. The lower field where compression conditions prevail. And the upper field, where the prevailing tensile conditions and intense seismic destruction of the rocks of the crust and upper mantle. The heat flux distribution shows the manifestation of the convective heating mechanism in the earth's crust over the most permeable fault zones.

The study of the composition of the gas phases and melt inclusions suggests that the partial melting of metasomatized ultrabasites occurs in the range of 1150 ° C <T <1200 ° C.

In accord with the composition of the glassy phase in the melt inclusions of spinel crystals, the harzburgite metasomatism in the local melting sites is associated with brine melts that bringing Ca, K, Na, Si. C. The work was financially supported by the Russian Foundation for Basic Research, Grants No. 16-29-15131, 16-01-00729.

References

Arai S., Ishimaru S. Insights into Petrologycal Characteristics of the Lithosphere Mantle Wedge beneath Arcs through Peridotite Xenoliths: a Review.// J. Petrol., 2008. V.49(4), 359-395.

Tomilenko A.A., Kovyazin S.V., Sharapov V.N., Timina T.Yu., Kuzmin D.V. Metasomatic recrystallization and melting of ultrabasic rocks of mantle wedge beneath Avacha Volcano, Kamchatka // ACROFI III and TBG XIV Abstracts Volume / SB RAS IGM, Novosibirsk: Publishing House of SB RAS, 2010, p. 248-249.