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

Abstract

Bezymianny volcano supply on the surface numerous xenoliths, revealing the composition of the crust containing the magmatic system and the processes occurring within it. In this study, we present data on the xenoliths from the upper crust that were partially melted and recrystallized (pyrometamorphosed) in the shallow chamber of Bezymianny volcano. Some xenoliths contain relics of primary igneous associations, and some contain relics of prepyrometamorphic hydrothermally alteration. Thus, protoliths of pyrometamorphosed rocks could be reconstructed, and hydrothermal processes could be determined for rocks previously altered with fluids. The most common xenoliths are moderate-K andesites, basaltic andesites, and basalts from Kamen and Bezymianny volcanoes. During pyrometamorphism, a new microgranoblastic paragenesis forms, consisting of homogenous pyroxenes, plagioclase, and Fe-Ti oxides, sometimes surrounded by glass. Xenoliths of plateau basalts from the Klyuchevskaya group of volcanoes (high-K trachyandesitic basalts) are less common. Some of plateau basalt xenoliths contain trace of quartz-carbonate-sulfide mineralization, which was formed before the capture of xenoliths and their pyrometamorphism. A hydrothermally altered rock was melted and recrystallized after xenoliths were captured by magma, resulting in a Fe-wollastonite-hedenbergite association (sometimes with garnet), which is not typical for Bezymianny. The copper content of these xenoliths is anomalously high (up to 1500 ppm).