Plagioclase Picrites in the Kamchatsky Mys Peninsula, Eastern Kamchatka

摘要

The zone of serpentinite melange in the Kamchatsky Mys Peninsula was found to contain highmagnesium ultramafic volcanic rocks, viz., plagioclase picrite (oceanite) with a MgO concentration of 22.5– 25.8%. We evaluated the petrochemical and geochemical characteristics of these rocks, as well as their min- eral compositions. The olivine phenocrysts make up 50–60% of the rock volume; their composition (mostly 87–89 mol % Fo) and the composition of melt inclusions in them indicate their origin from a picritic melt with an additional cumulative enrichment in olivine. The geochemical parameters (Zr/Y = 3.1, Th/Yb = 0.14–0.18, Nb/Yb = 2.39–2.66, La_((N))/Sm_((N)) = 1.0–1.1, La_((N))/Yb_((N)) = 1.24–1.42) indicate an oce- anic genesis of these rocks affected by a mantle plume.