Geology and petrology of the lava complex of Young Shiveluch Volcano, Kamchatka

Detailed geological and petrological-geochemical study of rocks of the lava complex of Young Shiveluch volcano made it possible to evaluate the lava volumes, the relative sequence in which the volcanic edifice was formed, and the minimum age of the onset of eruptive activity. The lavas of Young Shiveluch are predominantly magnesian andesites and basaltic andesites of a mildly potassic calc-alkaline series (SiO2 = 55.0–63.5 wt %, Mg# = 55.5–68.9). Geologic relations and data on the mineralogy and geochemistry of rocks composing the lava complex led us to conclude that the magnesian andesites of Young Shiveluch volcano are of hybrid genesis and are a mixture of silicic derivatives and a highly magnesian magma that was periodically replenished in the shallow-depth magmatic chamber. The fractional crystallization of plagioclase and hornblende at the incomplete segregation of plagioclase crystals from the fractionating magmas resulted in adakitic geochemical parameters (Sr/Y = 50–71, Y < 18 ppm) of the most evolved rock varieties. Our results explain the genesis of the rock series of Young Shiveluch volcano without invoking a model of the melting of the subducting Pacific slab at its edge.