New data on deep-seated structure of the Central Kamchatka depression (CKD) and rock composition of the basement are represented in this paper. Structural position of the Quaternary volcanoes is defined. Based on the geologic-geophysical data a zonal structure of the CKD is found. Margins of the three large longitudinal structural zones are distinguished and defined: depressive East and West and buried Khavyvenka rises. A block structure of CKD is distinctly fixed within the mentioned zones. Geophysical data testify to the anomalous permeability and active geothermal-fluid conditions within the CKD which correlates well with its riftogenic origin.

Among the hypotheses of andesite formation was distinguished a group of «aqueous» models which assume an active participation of water in this process. From the position of «aqueous» genesis of andesites under analysis are mechanisms which could lead to lowering of water concentration and increasing of temperature of the melts to the values being in accordance to estimations of conditions of crystallization of andesites. At the depth more than 10 km such mechanism could be represented by supply into the magma of large amounts (tens percent of mass) of high-temperature depth-derived fluids having a low percentage of water. At the depth less than 5 - 10 km it could be a bulk crystallization under adiabatic decompression. The conclusions obtained are discussed on the example of the Bezymyanny volcano. For reasonable testing of the «aqueous» models it is necessary to determine more precisely the depthes of formation of phenocrysts of andesites.