We provide new evidence that bears on the geological structure, history of evolution, and structural setting for the Bol’shoi Semyachik Volcanic Massif in Kamchatka. The new Ar–Ar results for dating of volcanic rocks allowed significant advances in updating the stratigraphy and history of the evolution of the area of study. We discuss the distribution of centers of volcanic and hydrothermal activity in the Bol’shoi Semyachik Massif area. The distribution suggests that the volcanism in the area is progressively migrating south eastward. It is shown that all thermal occurrences, such as sets of steam jets, thermal springs, and heated patches (evidence of present-day activity), are also displaced into the southeastern part of the massif. It was concluded that these patterns are not accidental, but are controlled by dipping magma-conducting and fluid-conducting faults that bound a major basement low on the southeast. The low had been identified earlier from geophysical observations. The dip gives the result that the magma and fluids rise to the surface and simultaneously deviate eastward and southeastward, where the youngest occurrences of volcanic activity and present-day thermal features are found today.

The Ziminy Sopki Volcanic Massif is remarkable for its co-formation from magmas of different potassium alkalinity manifested by three rocks associations (series) with individual evolutional trends: I — andesite-basalts — andesites — dacites; II — andesite-basalts — the intermediate composition andesites; III — high potassium andesite-basalts. Variations of rocks from the revealed series manifest themselves in the above mentioned mineral associations, and the discreteness of rocks regression lines evidence on quite autonomous parental magmas. Orthogonal trends of minerals composition alterations in andesite-basalts with the vector correlating with the potassium alkalinity increase in rocks of associations evidence on existence of the process leading to the enrichment of these magmas with potassium. Thus, we can conclude that, within the single penetrated magmatic system, there are deep intermediate chambers with different conditions for formation of the initial andesite-basalt magmas, which during volcanic activity directly associated with the deeper parental basaltic magma.

Рассматриваются геологическая история и петрология крупного полигенного вулканического сооружения верхнеплейстоцен-голоценового времени. Этот долгоживущий вулканический центр знаменателен совместным проявлением магм базальтового и трахибазальтового составов, представленных базальт-андезитовой и трахибазальт-трахиандезитовой сериями. Делается вывод о генетической автономности сосуществующих родительских магм, генерированных в разных глубинных источниках области верхней мантии. Разнообразие составов вулканитов обязано многостадийной пространственно-временной кристаллизационной дифференциации магм и смешению последних в промежуточных очагах.