Understanding how pre-existing mantle wedge depletion shapes arc magma chemistry, distinct from subduction inputs, remains a key challenge in petrogenesis studies in subduction zone volcanoes. Here we present new high-precision Zn isotopic data (expressed as delta Zn-66, relative to JMC(Lyon) standard) for 62 arc lavas from western Pacific arc-front (Mariana, Izu, and Kurile) and rear-arc (Mariana) volcanoes. After correcting delta Zn-66 for early fractional crystallization, our results show that near-primitive arc-front lavas exhibit delta Zn-66 values systematically similar to 0.06 parts per thousand lower than rear-arc lavas, similar to 0.11 parts per thousand lower than back-arc basin and mid-ocean ridge basalts. Crucially, delta Zn-66 correlates positively with source depletion indicators (e.g., Ta/Zn, Nb/Yb), but shows no correlation with slab input proxies (e.g., Ba/La, Ce/Mo, delta Mo-98), demonstrating that subduction fluids/melts minimally affect Zn isotopes in arc magmas. Notably, progressive mantle depletion (e.g., from lherzolite to harzburgite) drives a compositional transition and corresponding delta Zn-66 variation in residual mantle spinel (e.g., from Al-rich to Cr-rich). This source lithology transition triggers inter-mineral isotopic re-equilibrium, which in turn decreases the Zn isotope fractionation factor (alpha Zn-66(Melt-Residue)) in more refractory sources. By incorporating this effect, our newly-developed partial melting models reveal that Mariana arc-front magmas formed from 5-10 % melting of mantle previously depleted by 9-12 % melt extraction, whereas rear-arc magmas derived from 5 % melting of less depleted mantle (3-9 % pre-depletion). This pre-depletion at a mature oceanic arc is most likely driven by prior melt extractions during back-arc spreading. Our Zn isotopic data therefore provides direct evidence that ambient mantle wedge infertility profoundly controls the geochemical diversity of arc-front magmas.

The full range of effects of strong volcanic eruptions on the electrical characteristics of the atmosphere is not yet fully understood. On the 10 April 2023, the largest eruption in recent decades of the Shiveluch volcano in Kamchatka occurred. At the same time, a sharp increase in electron concentration was observed in the F layer of the ionosphere above the volcano. Simultaneously, at a distance of 450 km from the volcano, an intense anomaly was observed in the vertical component of the electric field potential gradient in the surface atmosphere. At this distance, the anomaly could not have been caused by a space charge of volcanic ash. The article examines the atmospheric–electrical effects of a volcanic eruption and proposes a physical mechanism for these phenomena. The formation of strong electric field positive jump as result of volcano eruption was confirmed by the consecutive Shiveluch volcano eruption on the 18 August 2024.

The genesis of leucogranite magmas is important issue of geodynamics, petrology and ore geology because leucogranites are associated with collisional belts, partial melting of sedimentary source rocks, and may host rare metal (Sn, W, Li, Nb-Ta, and Be) mineralization. To establish the petrogenesis of large leucogranite intrusions, detailed studies of petrography, mineralogy, fluid regime, and the material and isotopic composition of rocks are required. The paper reports results of the studies of the Delbegetei massif of the intrusion in Eastern Kazakhstan. The massif is composed predominantly of leucocratic granites, while syenogranites are subordinate. Rocks of the massif belong to shoshonitic and high-K calc-alkaline series; demonstrate a predominance of K over Na, high ferroan and high contents of LREE and HFSE; which allows them to be classified as A-type granites. The age of Delbegetei massif, estimated by the U-Pb zircon dating, varies in the range 249-240 Ma, which correspond the Early-Middle Triassic. The differences in rock composition and in temperatures of zircon saturation allow supposing that syenogranites and leucogranites formed from different parental magmas. Syenogranite magma formed as a result of partial melting of metamorphosed volcanic rocks (andesidacites or dacites) with possible influence of mafic magmas. Leucogranite magma formed as a result of fluid-present partial melting of metaterrigenous sedimentary rocks. Leucogranite magma underwent the feldspars differentiation in the fluid-present conditions. This led to composition variations of leucogranites. Analysis of the geological position, age and composition of the rocks allows concluding that the Delbegetei massif formed at the Early Triassic in an intraplate geodynamic setting and that the activity of the Siberian mantle plume is the most probable reason for their formation.

An Erratum to this paper has been published: https://doi.org/10.1134/S1028334X23070164

For the first time, high-alumina mineral associations including rare minerals of the rhönite-kuratite series were found in post-caldera lava flows of the Kudryaviy and Menshiy Brat volcanoes (Kuril Islands). These lava flows are composed of olivine-bearing basalts and andesite-basalts of the calc-alkaline series. Partially crystallized olivine-hosted melt inclusions in these rocks contain high-alumina daughter phases. Residual glass with up to 25 wt% Al2O3, Al-pyroxenes and spinel with minerals of the rhönite subgroup were identified. The rhönite-kuratite series minerals are characterized by strong variations in Al, Fe2+, Fe3+, Mg, Si, as well as very low Ti, which makes it possible to name it a low-Ti Fe2+ analogue of rhönite with the formula (Ca,Mg,Na)4(Mg,Fe,Fe, Al,Ti,Mn)12O4[Si8.2Al3.8O36] – (Ca,Na,Mg)4(Fe,Mg,Al,Fe,Ti)12O4[Si6.78Al5.22O36]. It is assumed that high-alumina daughter phases form in olivine-hosted melt inclusions through water accumulation in the trapped melts during crystallization of the host olivine on the walls of melt inclusions. Water-rich melts can inhibit early crystallization of plagioclase, which promotes enrichment of the residual melt in Al2O3.

An Erratum to this paper has been published: https://doi.org/10.1134/S1028334X23070164

Cryogenic cave carbonates (CCCs) genetically related to permafrost are of special interest in paleoclimate research. Their 230Th/U ages provide unique information about the former presence and depth of permafrost in presently permafrost-free areas. Details of CCC formation processes and their diagnostic features, however, remain incompletely understood. In this paper, we report the results of a study of CCCs from two northern Eurasian caves, currently located in permafrost-free rocks. CCCs in the caves occur in a wide range of grain sizes (micrometers to several centimeters). Stable isotope values of different CCC morphotypes (size range of 0.1 to 4 mm) plot within relatively tight clusters in 818O-813C space, regardless of their grain size, indicating that CCCs of the same morphotype, but of different size, formed simultaneously at certain freezing stages. The clusters conform to an overall negative "freezing trend" in 818O-813C space. The position on the trend indicates the relative age of individual morphotypes; scatter of the data in 818O-813C space suggests multiple episodes of freezing (permafrost formation). The systematic characterization of CCC morphologies and the study of fine-size fractions of CCCs provide important insights into the processes involved in CCC formation in caves located in permafrost.

The present paper considers petrographic and geochemical features of rocks of the Tigrinoe and Zabytoe stocks, provides their mineral composition, the results of the detailed study of micas and mineral-forming inclusions in quartz. It is shown that the development of ore-magmatic systems (OMSs) of the Zabytoe and Tigrinoe deposits is associated with the same rare-metal Li–F melts. It is confirmed that granitoids of the Tigrinoe stock can be considered as more differentiated analogs of granitoids of the Zabytoe stock. New data concerning the differences in the history of the magmatic stage of development of the OMSs of these deposits are presented. The evolution of melts of both deposits took place at high fluid pressure. Differences in the scale of ore mineralization of the two RMSs under consideration could be due to different fluid regime of magmatic sources evolution and more significant participation of transmagmatic fluid flows in the development of the Tigrinoe OMS.

For the first time, high-alumina mineral assemblages including rare minerals of the rhönite–kuratite series were found in postcaldera lava flows of the Kudryavy and Menshiy Brat volcanoes (Kuril Islands). These lava flows consist of olivine-bearing basalts and andesite-basalts of the calc-alkaline series. Partially crystallized olivine-hosted melt inclusions in these rocks contain high-alumina daughter phases. Residual glass with up to 25 wt

--The paper presents data from a comprehensive study of granitoids identified in the Mayorka intrusion that is located in the western part of the Altai Mountains. It is shown that the massif is composed of rocks of four intrusive phases, the age of these rocks ranges from 391 to 372 Ma, and the intrusion of the main volume of granitoids dates back to a relatively short interval of 386-384 Ma. The massif contains rocks of two geochemical types. The first type is differentiated calc-alkaline granite-leucogranites with near-clark contents of high-field-strength elements and rare earth elements: epsilon(Nd)(T) = + 4.3 & mldr;+ 4.5 and sigma O-18 V-SMOW = +10.7 & mldr;+11.2 parts per thousand. The second is alkaline and moderately alkaline A-type alyaskites, strongly enriched in high-field-strength elements and rare earth elements, having epsilon(Nd)(T) + 5.3 and sigma O-18 V-SMOW = +11.6 parts per thousand. Granitoids of the first group are of crustal source, while the rocks of the second group contain a significant portion of mantle material. The near-simultaneous introduction of these melts to the level of formation of the intrusion causes their interaction and the formation of hybrid magmas. Low crystallization temperatures of granitoids (<700 degrees C) and the presence of syngenetic melt and fluid inclusions in most rock varieties indicate a high fluid saturation of the melts. The abundance of leucogranites, whose geochemical characteristics cannot be explained from the standpoint of shallow differentiation of primary magmas, indicates the leading role of fluid-magmatic interaction processes in the formation of high-silica magmas.

Inclusions of the mineral-forming media in quartz of the Vysokogorskoe deposit are studied in detail. The compositions of the melts correspond to peraluminous potassium granites of normal alkalinity, depleted in rare alkalis, F, and Cl. The water content in the melts reached 7–9 wt %; CO2 and CH4 were also important in mineralizing fluids. Quartz crystallized at 620–650°C. Assemblages of four types have been identified as primary fluid inclusions: (1) inclusions of carbonate or sulfate aqueous solutions coexisting with melt inclusions, (2) low-density vapor-dominated primarily magmatic inclusions, (3) presumably postmagmatic low-salinity aqueous and vapor-dominated inclusions, and (4) multiphase fluid inclusions associated with vapor-dominated ones also formed at the postmagmatic stage. Daughter pyrosmalite–(Fe) and hibbingite, which was found for the first time in inclusions from quartz of the Vysokogorskoe deposit, made it possible to characterize the solutions as high-salinity chloride Na/K and Fe2+. Presumably, those solutions may have been the most efficient in Sn transport during the formation of fluid–explosive breccias and vein mineralization of the Vysokogorskoe deposit. The magma chamber itself most likely served as a heat source and, to a large extent, a source of aqueous fluid for the hydrothermal system of the deposit.

Geochemical study of volcaniclastic material and radiocarbon dating of charred plant debris from Holocene deposits of the Guram site, which is located in vicinity of Vetrovoi Isthmus on Iturup Island, demonstrate that an explosive eruption (VEI 4-5) occurred there about 2000 years ago. The geochemical and age similarity with the tephra of marker layer CKr that was distinguished on Iturup, Urup, Simushir, Rasshua, and Matua islands of the Kuril Island Arc led to the conclusion that this eruption is possibly a source of this tephra. The data presented are proposed as a motivation for revision of the volcanic hazard on Iturup Island.

This paper presents data on the geological position, geochemical features, main mineral composition (micas, feldspars), and melt and fluid inclusions in quartz from Aba high-silica leucocratic granitoids in the western part of the Talitsa batholith, Russian Altai. According to these new geochemical data, the granitoids are classified as S-type, meaning they are formed via the partial melting of metasedimentary source rocks. Geological data and oxygen isotope composition analysis indicate that major-phase granitoid magma evolution took place at the level of intrusion formation, whereas the parent melt of late-phase leucogranite evolved in a deeper chamber. The geochemical features (HFSE and REE, and REE spectra) of the granitoids indicate significantly higher differentiation in the late leucocratic phase. The presence of coexisting syngenetic melt and fluid inclusions shows that leucogranite magma was already saturated with volatiles in the early crystallization stages. Based on the new data presented in this work, the Aba rock formation is associated with the volatile saturation of magmatic melts, the exsolution of a fluid phase, and magma degassing.

Convectively mixed layer (CML) forms due to radiatively driven convection (RDC) in the upper part of the water column in shallow ice-covered lakes. The spatial structure of this layer has been very poorly studied. The long-standing hypothesis postulates a continuum of convective cells in this layer. The invariant analysis is used to reveal the spatial inhomogeneity of the turbulence parameters within CML and their evolution during the daily cycle of RDC based on solar radiation, water temperature and current measurements in a small shallow ice-covered lake. The values of all six components of the Reynolds-stress tensor are estimated using the method suggested by Bogdanov et al. (Fundam Prikl Gidrofiz 14:17–28, 2021). A high level of turbulence anisotropy within CML was observed throughout the entire measurement period (10 days). Anisotropy invariant maps demonstrate multiple transitions between prolate (rod-like) and oblate (disk-like) types of axisymmetry, without reference to the diurnal cycle of RDC. The dynamics of anisotropy tensor eigenvalues, in contrast to that of the stresses per se, also exhibited no connection with the diurnal cycle of RDC. Considering the presence of mean geostrophic drift in the studied lake, the revealed changes of axisymmetry types and anisotropy tensor eigenvalues are most likely associated with the spatial inhomogeneity of turbulence within the convective cells moving through the measurement zone. The absence of an explicit dependence of turbulence anisotropy on the diurnal cycle of RDC suggests that convective cells "survive" at night and, together with geostrophic drift, maintain the turbulence of the mixed layer.

This paper provides information on the 2022 eruptive activity of Ebeko Volcano. Phreatic explosions had been occurring in the crater lake from January 22 to June 13 due to water seepage through a plug in the upper part of the magma conduit with subsequent boiling. Vulcanian type explosions started since June 14 and dried the lake. The ash particle-size distribution changed toward smaller sizes. Petrographic, mineralogical, and geochemical studies of the tephra define this period as a phreatomagmatic eruption based on the presence of fresh juvenile material. Interaction between magma and waters of the Ebeko hydrothermal system results in its depletion in alkali and enrichment in silica. We hypothesize that the formation of amorphous water-bearing silica in the form of numerous segregations and its subsequent dehydration can favor the volcano’s explosive activity.

The paper represents new data on the formation conditions of basalts from post-caldera volcano Menshiy Brat (Medvezhia caldera, Iturup Island). Liquidus mineral assemblage is composed of olivine (Fo up to 90.1 mol. %) and chromium spinel (Cr# = 0.46–0.6), which crystallized at 1090–1170°С and oxygen fugacity NNO +0.6 (σ = 0.2) – NNO +0.2 (σ = 0.14). The study of melt inclusions in the liquidus olivine demonstrated that its parental melts have low-alumina, low-potassium compositions with up to 15.5 wt. % MgO and with an average water content of 5.5 wt. %. The data on volatile contents in the olivine-hosted melt inclusions suggest that the basic melts appeared due to partial melting of essentially peridotitic source with a small admixture of an olivine-free component at 1225°С under active influence of the slab-related fluids. These fluids were separated from the subducting slab at 670–705°С and depths of 95–105 km beneath the Iturup Island. The results of this study enhance our understanding of the evolution of basic magmas that serve as a heat and volatile supply during the formation of large calderas.