Sulfide Mineralization in Pyrometamorphosed Upper Crustal Xenoliths, Bezymianny Volcano, Kamchatka

Abstract

Bezymianny volcano eruptions transport numerous xenoliths to the surface. Crustal xenoliths contain unique information about the crust structure and composition of crustal rocks located around the active magmatic system. We describe the chemical and mineral composition of upper crustal xenoliths that pyrometamorphosed (recrystallized and partially melted) in the Bezymianny shallow chamber. We reconstructed protoliths and hydrothermal processes for several rocks, which were previously altered, based on pre-pyrometamorhic relics (primary igneous associations in some xenoliths and rare hydrothermal relics). Moderate-K andesites, basaltic andesites, and basalts of Kamen and Bezymianny volcanoes dominate among the xenoliths. During pyrometamorphism, a microgranoblastic assemblage composed of homogenous pyroxenes, plagioclase, Fe-Ti oxides, and interstitial glass is formed in these xenoliths. Less common xenoliths are presented by high-K basaltic trachyandesite (plateau basalt from the basement of the Klyuchevskaya group of volcanoes). Quartz–carbonate–sulfide mineralization is present in some of them, which formed prior to xenolith entrapment and pyrometamorphism. When xenoliths were entrapped by magma, recrystallization of hydrothermally altered rock produced Fe-wollastonite–hedenbergite association (in some cases with garnet), untypical for Bezymianny. Some of these xenoliths have extremely high copper content (up to 1500 ppm).