Na metasomatism in the island-arc mantle by slab melt-peridotite interaction: Evidence from mantle xenoliths in the north Kamchatka arc

The Pliocene (7 Ma) Nb-enriched are basalts of the Valovayam Volcanic Field (VVF) in the northern segment of the Kamchatka are, Russia, host abundant mantle xenoliths, including spinel Iherzolites. Textural and microstructural evidence for high-temperature, multi-stage, creep-related deformations in spinel Iherzolites supports a sub-are mantle derivation. Pyroxene chemistry indicates the existence of two compositional suites: (I) a Cr-diopside suite with low-Ti, moderate-Al clinopyroxene compositions, and (2) an Al-augite suite with high Al and Ti, and law Cr concentrations in clinopyroxene. Some spinel Iherzolite xenoliths contain metasomatic Al-augite-type clinopyroxene, Al-ii spinel, and felsic veins similar to trondhjemite melt. The Al-augite series xenoliths typically contain high-Na plagioclase, Cr- poor, Al-Fe-Mg and Al-Ti-Fe spinels, with occasional almandine-grossularite garnet and high-Al and -Na pargasitic amphibole. Pyroxene and spinel compositional trends suggest that the Cr-diopside series xenoliths from the VVF Nb-enriched are basalts represent an island-are mantle affected by a metasomatic event. Occurrence of high-Na plagioclase and trondhjemitic veins favors the addition of a metasomatic component with high Na, Al and Si to the northern Kamchatka are mantle. Trondhjemitic veins, representing siliceous slab melts, compositionally exemplify the metasomatic component. Na metasomatism by peridotite-slab melt interaction is an important mantle hybridization process responsible for are-related alkaline magma generation from a veined sub-are mantle.