Simulation of nonisothermal metasomatism of peridotite from mantle wedge beneath the Avacha group of volcanoes (Kamchatka)

Abstract

Comprehensive studies of mineralogy, fluid and melt inclusions, and gas phase in minerals from a representative collection of peridotite xenoliths that underwent metasomatism and convective partial melting in the mantle wedge beneath Avacha Volcano were used to simulate interactions between mantle wedge material and magmatic fluids of constant and variable compositions at different depths, as well as metasomatic effects of fluids derived from subduction slabs. 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. The compositions of the Avacha xenoliths and crustal rodingite from Kamchatka compared with results of physicochemical modeling suggest that eruptions of Avacha Volcano brought metasomatized material of the upper mantle wedge to the surface. The rocks underwent multistage metasomatism along cracks in a relatively narrow temperature range. Such processes are apparently common to seismically deformed permeable lithosphere above magma reservoirs. However, the mineralogical zoning of the Kamchatka crustal rhodingites differs from that in cracked metasomatic peridotite above the sources of magmatic fluids in the mantle wedge beneath the Kamchatka arc.