No 1 (2025)

In our paper we represent the first data on the Holocene explosive activity of Zavaritsky volcano, the largest caldera center on Simushir Island (Central Kuriles). For the first time, we reconstructed the chronology of explosive eruptions of this volcanic center for the past 10 000 years, as well as estimate the parameters of its largest eruptions. In total, more than 40 tephra horizons have been identified, which allows us to estimate the frequency of eruptions: 1 event in 250 years. Constructed age model allowed us to determine the age of most eruptions. Volcanic glasses of Holocene tephras correspond in composition to low-potassium basaltic andesite-rhyolites, while the very low K₂O content makes it possible to fairly confidently distinguish Zavaritsky tephra not only from the tephra of neighboring moderate-potassium volcanoes, but also from the tephra of other low-potassium volcanoes of the Kuril-Kamchatka Island arc. Holocene activity of Zavaritsky volcano started with two powerful eruptions with a conservatively estimated magnitude (M) of 6.4 and 5.6, which occurred about 9.5 and 9.2 thousand years ago (ka BP). Tephra from the first eruption (ZV-1) spread to the northeast and was found as far as northwestern North America. Tephra from the second powerful eruption (ZV-3) spread north and was found in sediments of the Sea of Okhotsk. Volcanic glass of ZV-1 tephra is characterized by rhyolitic composition with the highest SiO₂ content (72.5‒74 wt. %). Glasses of the ZV-3 tephra varied in composition from dacites to rhyodacites (65‒71.9 wt. % SiO₂). The products of subsequent eruptions were represented by scoria with glasses of dacite — andesite and basaltic andesite composition. Dacitic glasses reappeared only in the tephra of the last large explosive eruption that occurred early before the middle of the 19th century. Our studies revealed the catastrophic explosive eruptions of Zavaritsky volcano during the Early Holocene and sustained activity of this eruptive center throughout the Holocene. The appearance of high-silica glasses in the tephra of the last powerful eruption (ZV-40) indicates a possible strong eruption in the near future.

Epithermal Au–Ag mineralization of the Pechalnoe deposit is of considerable interest, since it was formed in carbonaceous terrigenous strata of the basement of a volcanic dome structure, at a distance of about 200 km from the border of the Okhotsk-Chukchi marginal continental volcanic belt.The geological structure of the Pechalnoye deposit is two–tiered: quartz-adularic and quartz Au–Agveins are localized in keratinized terrigenous rocks of the lower tier, and quartz rhyolites and komendites of the Pechalninsky strata of the upper tier contain potentially industrial REE mineralization. Productive veins form three zones of sublatitudinal strike, the length of the veins in which is 200‒300 m,sometimes 640, 840 m; average thickness 0.1–3 m, rarely up to 6.2 m, average contents: Ag — 266 g/t,Au — 4.4 g/t. The following mineralogical features of ores have been established: low sulfidity (1–2%);native Ag, low-grade Au, polybasite, and highly selenic acanthite act as productive minerals, in addition,arsenic pyrite, arsenopyrite, pyrrhotite, ferruginous sphalerite, chalcopyrite and marcasite are quite widely developed in ores. The geochemical features of the ores are in good agreement with the mineral composition. The ores are enriched with a fairly wide range of trace elements (according to the rating): Ag, Au, As, Sb, Se, W, Tl, Li, Be, Bi, Cs, Mo, the predominance of light lanthanides over heavy ones has been established, very low Eu/Sm ratios  (<<1), slightly inclined nearchondrite spectra (without distinct Europian minima or maxima); the ratio of Ce/Ce* and Eu/Eu* values indicate oxidative conditions during ore formation; the REE spectra are dominated by light “hydrophilic” lanthanides of the “cerium” group; the REE varies widely. The obtained mineralogical and geochemical data allow us to attribute the mineralization of the Pechalnoye deposit to the selenium subtype of the lowsulfidized class of epithermal deposits. According to geological and mineralogical-geochemical data, the deposit can be classified as poorly eroded, which makes it possible to predict the identification of new ore bodies that do not come to the surface.

The article considers a number of problems solved to one degree or another when forecasting the most dangerous — strongest earthquakes. The most important of them are: the problem of the effectiveness of seismic forecasting based on the idea of scenarios — basic patterns of development of foci of the strongest earthquakes; the problem of monitoring the development of such scenarios based on seismological data; the problem of modeling the relationship between seismic and geodynamic processes that determines these scenarios. To solve the last two problems, the article proposes to use the concepts of the energy and dynamic spectra of seismic activity of the geoenvironment, and the peculiarity of the proposed solution is the introduction of the mathematical concept of information certainty. As an example of using the proposed methods, the article presents a justification for a hypothetical multi-year oscillatory motion during the submersion of the oceanic plate in the Kamchatka subduction zone with a period of about 8.57 years. It is assumed that such oscillations largely determine the most probable periods of occurrence of regional strongest earthquakes.