The formation of large volumes of rocks of acid volcanism is an important process in the geothermal regions of Kamchatka. Currently, the hypothesis of a catastrophic eruption of a supervolcano in the Banno-Paratunsky geothermal area has become widespread. The basis for this concept is some data on the formation of a thick stratum of acidic and ultra-acidic rocks, which is known as the Karymshinsky volcanic complex. It is located in the volcano-tectonic depression. Caldera not found. There are no signs of the movement of acidic products of a powerful explosion (~ 275 km3). It is assumed, that the internal energy of acidic magmas in this region is insufficient for the formation of such a mass of eruption products. In this regard, it is assumed that this concept is not sufficiently substantiated. Recently, evidence has appeared that large-scale ignimbrites and rhyolites are formed from metamorphic rocks. In this regard, we propose a new concept of their formation, based on the role of hydrothermal metamorphism in the bowels of artesian hydrothermal systems. These systems are located in depressions between long-lived volcanic centers. As a result of the discharge of high-temperature groundwater flows with silica gel in depression, a siliceous layer is formed with a thickness of 1-2 km. It plays the role of an upper waterproof horizon with the properties of a heat insulator (cap rock). During periods of glaciation, such depressions are accumulators of powerful glaciers. They complemented the action of cap rock. The formation of cap rock horizons was accompanied by both an increase in temperature and an increase in gas concentrations (CO2, CH4, H2, and others). The transformation of siliceous strata of cap-rock into ignimbrites, welded tuffs and acid melts of acid composition took place. Under the influence of the weight of glaciers and surrounding rocks, these plastic formations gradually rose up until they appeared on the surface in the form of extrusions and flows of welded tuffs (ignimbrites).

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