The Bol’shoi Semyachik Volcanic Massif, Kamchatka: Geological structure and structural setting

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 southeastward. 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.