No 1 (2023)

Lake Kipyashchee (Boiling) with an area of ~4.6 ha and a maximum depth of 25 m fills the explosion funnel near one of the extrusive domes of the Golovnin volcano caldera. The water of the lake is ultra-acid (рН = 2.2–2.5) of the chloride-sulfate type with a mineralization of 2.0–2.2 g/l. The water temperature on the surface varies from 30 to 100°C, the average is 37°C. The flow of the lake is carried out through the Protoka in the lake Goryachee (Hot) is 120 l/s (August 2021). The hydrothermal output of magmatic Cl and S (as SO₄) from Lake Kipyashchee is 10 t/day and 5.4 t/day, respectively. For the first time, the total diffusive removal of carbon dioxide from the surface of Lake Kipyashchee was estimated as 5.4 tons/day. Obtained from the results of field work in 2020–2021 geochemical data indicate an increase (compared to 2015) in hydrothermal activity in the Golovnin volcano caldera.

The article presents the results of our gravimetric, seismic and electromagnetic research, as well as the data on deep seismicity of the lithosphere in the area of the active Avachinsky and Koryaksky group of volcanoes, which is the part of the East Kamchatka volcanic belt. We managed to develop the comprehensive geophysical model of the Earth’s crust and lithospheric mantle of this area. Based on the distribution scheme of the Earth’s crust geophysical inhomogeneities in general, and particularly beneath Avachinsky Volcano, we revealed specific features for both intracrustal fluid saturation and conduits through which deep fluids rise to the upper part of the crust. According to the comprehensive model, stresses arising at the margins of zones with different defluidisation conditions, in particular, in the lower part of the crust, and characterizing by contrasting electrical conductivity values, are one of the most important reasons for active seismicity beneath active volcanoes. The general scheme of the deep lithospheric processes and the volcanoes magma feeding system specific features are based on the obtained results and the data on the local seismic tomography. It is assumed that Avachinsky Volcano, being a part of the active Avachinsky and Koryaksky group of volcanoes, is connected with the asthenospheric layer at a depth of ~70–120 km, from which fluid/melts enter into the magma chamber located in the lower crust and then, under the influence of the heat from the lower crustal source, the peripheral chamber is formed in the upper crust beneath the volcano’s cone.

Microxenoliths of sedimentary-marine carbonatoliths in fumaroles of the crater zone of the Second Cone of the BTFE Northern Breach, which were exposed to exhalative-pneumatolytic fluids with the formation of many compounds with mixed carbonate-sulfate-chloride anionic radicals, which are considered as two interclass and nine intertype crystal chemical hybrids, are studied at the expense of carbonates. The pattern of heterogeneity of mineral parasteresis revealed in the altered microxenoliths is interpreted by us as the result of a successive epigenetic transformation of primary carbonates, first into sulfate-carbonates, then into carbonate-sulfates, and then into chloride-carbonate-sulfates and chlorides. Judging by the absence of signs of phase heterogeneity, the investigated crystal-chemical hybrids are homogeneous solid-phase mixtures of carbonates, sulfates, and chlorides in different proportions. The carbonates in microxenoliths in terms of carbon isotope composition (δ¹³С_PDB = –5.34 ± 0.62‰) and oxygen (δ¹⁸O_SMOW = 24.09 ± 1.05‰) correspond to carbonates of sedimentary-marine limestones redeposited under conditions of volcanic transport. The isotopic composition of sulfate sulfur (δ³⁴S = 1.5–2‰) varies within the range of fluctuations established for sulfates of volcanogenic origin. In carbon particles associated with microxenoliths, the isotopic compositions of carbon (δ¹³C_PDB = –27.37 ± 2.97‰) and nitrogen (δ¹⁵N_Air = 6.74 ± 2.48‰) tend to be similar to the mode of distribution of such values in the products of modern continental volcanism. The identified crystal-chemical hybrids are a typomorphic feature of the fumarous-exhalative facies and are considered as a previously unknown phenomenon of modern volcanism.