Melting and Multi-stage Metasomatism in the Mantle Wedge beneath a Frontal Arc Inferred from Highly Depleted Peridotite Xenoliths from the Avacha Volcano, Southern Kamchatka

Abstract

Peridotite xenoliths from the Avacha volcano, Kamchatka, derived from the mantle beneath the volcanic front of the Kamchatka arc, are mainly highly depleted clinopyroxene-poor harzburgites with highly forsteritic olivine (Fo 90^92) and high Cr-number spinel (05^07). The Avacha peridotites have experienced metasomatism to various extents, with the formation of metasomatic orthopyroxene replacing primary olivine, by infiltration of SiO2-rich fluids. The metasomatic orthopyroxenes can be subdivided into two textural types; (1) radially aggregated prismatic grains (opx II-1); (2) stout grains associated with interstitial glass and metasomatic minerals (opx II-2).The Avacha peridotites exhibit light rare earth element (LREE) enrichment relative to heavy REE (HREE), even in primary lithologies with52 vol. % of metasomatic orthopyroxene. However, the metasomatism has not altered the chemical character-istics of the Avacha peridotites significantly, and the Fo contents