Hybrid Metaandesites of Khangar Volcano, Sredinny Range, Kamchatka: Product of Interaction between Basaltic Magma and Basement Granitoids?

Abstract

Unique rocks were found in an outcrop of basement granodiorites in the southern part of the Khangar caldera. The bulk composition of these rocks corresponds to high-Mg andesite (SiO₂ 57–63 wt %, MgO 4–8 wt %, and K₂O 1.4–2 wt %). The rocks contain coexisting quartz, oligoclase, and olivine phenocrysts and a propylitic mineral assemblage (albite, calcite, chlorite, and epidote). The largest phenocrysts are similar in composition to granodiorite minerals (oligoclase An_22–28, quartz, and biotite). The olivine phenocrysts contain melt inclusions of basaltic composition (SiO₂ 45–48 wt %, MgO 7–10 wt %) with a high K₂O content (up to 1.6 wt %). We suggest that these rocks were produced by interaction of basaltic melt with silicic intrusive material and with the xenogenic material of the granitoid intrusion.