№ 5 (2024)

We have obtained the first data on the chemical composition of the eruptive materials from the explosive eruption of Bezymianny volcano on April 7, 2023. Our unique collection includes freshly sampled pumice lapilli from the eruption and juvenile blocks from pyroclastic flows. We have identified interesting patterns in both macro components and specific chalcophile elements, such as copper. The rocks we studied belong to medium-K two-pyroxene basaltic andesite (55.5‒57 wt. % SiO₂), with mafic enclaves characterized by a slightly more primitive composition (53.7 wt. % SiO₂). According to mineral geothermometry data, the phenocrysts of basaltic andesite crystallized at temperatures in the range from 940 to 960°C, while the formation of phenocryst rims and microlites occurred at 980°C, which corresponds to conditions immediately before the eruption. The composition of volcanic glass allows us to estimate the pressure at which the magma reached the last equilibrium with crystallizing phases before eruption (0.5‒0.6 kbar). Based on these findings, we have formulated hypotheses about the potential evolution of the shallow magma chamber of Bezymianny volcano during the period from 2017 to 2023.

16 morphometric relief parameters have been established, the positive anomalies of which correspond to seismically active areas in the Greater Caucasus region. Analysis of the four most informative parameters using the γ-operator in fuzzy logic has made it possible to create a scheme for a neotectonic activity index. This index was used together with the results of computer geodynamic modeling to identify zones of potential earthquake epicenters. This approach does not require detailed information on modern and past seismic activity, and can therefore be applied to areas that are seismologically understudied. In addition, a relationship between modern deformation and seismic activity is shown, as well as the possibilities of using the technique developed by Yu.V. Nechaev [Nechaev, 2010] to identify active fault zones.

Iceland is a unique example of a place, where rift zone of Mid-Atlantic Ridge appears onshore. Its morphological and tectonic features considerably differ from typical mid-oceanic ridge rift zones. The morphology and geodynamics of Icelandic rift western branch are formed by Iceland plume thermal influence that generated the North Atlantic Large Igneous Province. Icelandic rift western branch is characterized by ceasing tectonic and magmatic activity. Overlapping with the Eastern Rift Zone it forms rotating block of Hreppar Microplate that leads to tectono-magmatic activity decline northwards. Based on morphometric analysis of normal faults, the relative activity degree of individual parts of volcanic systems was revealed. For some parts, the activity changes in late Quaternary were traced. Obtained inferences demonstrate explicit differences in contemporary tectonic structure and dynamics of the rift zones and volcanic systems within them. For instance, transtensive Reykjanes Rift Zone, the southernmost one, has decreasing eastwards tectono-magmatic activity, which is connected with influence decrease of Reykjanes Ridge adjoining from the south-west. Its gradual southward shifting is observed that is explained by similar southward propagation of the most active Eastern Rift Zone and by the formation of new transtensive zone aggregating contemporary Reykjanes Rift Zone and South-Iceland Seismic Zone. In contrast, the Western Rift Zone develops independently from Reykjanes Rift Zone. It has the largest extension center in the area of Thingvallavatn Lake. In its northern part as within the Central Rift Zone, Holocene tectono-magmatic activity is very faint and is linked to glacioisostatic reactivation of more ancient structures. Revealed structural heterogeneities are traced in rift zone morphology as well. For example, within Western and Central Rift Zones, well-developed shield volcanoes are common. They consist of hyaloclasts predominantly. Within fissure swarms, individual lava shields are observed. In contrast, Reykjanes Rift Zone is characterized by absence of topographically expressed central volcanoes, and within fissure swarms, the chains of volcanic cones are present.