We consider the geologic occurrence and PT-conditions of the generation and crystallization of siliceous melts that formed volcanic structures within the Altai collisional system of Hercynides. The data on the geologic occurrence, internal structure, and petrogeochemical age of rocks are presented, as well as results of the thermobarogeochemical studies of inclusions in minerals. The performed investigations showed the presence of siliceous dacitic melts in the studied volcanic structures. These melts were generated in the lower crust (~10 kbar, 1000–1200 ºC) as a result of the partial melting of crustal substrates under the influence of high-temperature mantle melts.

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