We present here the first regional set of Sr-Nd-Pb isotopic compositions, major and trace element compositions and KAr ages for a representative suite of back-arc samples of the Sredinny Range (SR) of Kamchatka. Together with previously published analyses, this unique dataset allowed us to trace the source heterogeneity and invoke new mechanisms to explain the variably enriched geochemical signatures. Our results indicate that the Sr isotopic ratios and the LILE content of the studied rocks were mainly influenced by the subduction fluid. Neodymium isotopes, as well as the HFSE and REE distributions in the rocks, require a more complex explanation, depending on the geographical location of the studied samples and the age of their eruption. Melts representing Miocene rocks of the northern part of the SR and most of the rocks from the eastern and central flanks of the SR (from Miocene until present) were produced from a depleted MORB-like metasomatized mantle, and were then exposed to varying degrees of crustal assimilation and fractional crystallization. Higher HFSE contents and lower 143Nd/144Nd ratios in the western flank lavas, as well as high HFSE contents in the Quaternary lavas of the northern part of the SR and some of the lavas from the eastern flank of the southern part of the SR, require an alternative source for their enrichment. Delamination of the lithosphere explains the unusual, enriched signature of these rocks, whereas their variably enriched neodymium isotope ratios identify the various ages of the separation of the lithosphere from the mantle. The Nd isotopic composition of the rocks together with their HFSE content, therefore, serves as an unusual tracer for the enriched mantle domain, showing the presence of the older lithospheric blocks and indicating the timeframes for this source involvement in magma generation.

This paper is concerned with sublimates sampled in 2013–2020 in the near-crater zone and on the slopes of Alaid Volcano situated in the Kuril island arc. It was found that the near-crater zone contains native metals confined to zones of acidic leaching where the original lavas and tuffs have been transformed into opal-like rocks or rocks that are sharply enriched in hydroxides of trivalent iron. These zones were found to contain native gold, palladium, silver, chrome, copper, zinc and alloys of gold and palladium, copper and zinc, copper and tungsten. The mineral nomenclature in sublimates on the Alaid slopes is broader, while the temperature of their generation is lower. The ore minerals are dominated by copper-containing ones, and sublimates have been found with vanadium-containing minerals that belong to water-containing oxides and to silicates of vanadium. We have identified two genetic types of slope sublimates: (1) minerals that have crystallized from hydrothermal or vapor-hydrothermal solutions near vents of near-surface fumaroles and (2) copper and ferrous colloform formations that were generated by settling from colloidal solutions in shallow water of drying reservoirs, including small and large pools.

The study of minerals, melt inclusions, as well as natural glasses showed that two different melts contributed to the formation of ignimbrites of the Khangar Volcano. The first, providing the information on melt inclusions in plagioclase and quartz phenocrysts, represents the state of magma in a deep source. The other type of melt is responsible for the formation of glasses and microcrystals of feldspars in fiamme. Experimental and analytical studies of melt inclusions showed that crystallization of most plagioclase and quartz phenocrysts from ignimbrites of the Khangar Volcano occurred at temperatures of 840-960 degrees C and pressures up to 1.1 kbar, from the melt with water contents up to 3.23 wt.%, under the conditions of magma chamber. The presence of syngenetic primary melt and fluid inclusions in plagioclase and quartz phenocrysts from ignimbrites of the Khangar Volcano indicates phase separation ("boiling") of the melt with mass formation of & Scy;& Ocy;(2) microbubbles in magma. The other type of melt is secondary relative to magmatic systems of the Khangar Volcano and is formed by sintering and melting of tuffogenic volcanoclastic material. This melt contributed to the formation of fiamme in the examined ignimbrites. Based on the study of glasses and microcrystals of feldspars in fiamme, it was found that crystallization of oligoclase occurred at temperatures of 770-840 degrees C in the melt between the spherules (with water content up to 2.91 wt.%). Sanidine crystals grew over spherules at lower temperatures, 680-760 degrees C.

21—25 ноября 2022 г. Институт геохимии им. А.П. Виноградова Сибирского отделения Российской академии наук организовал и провел юбилейную Всероссийскую конференцию, посвященную 65-летию со дня своего основания и 105-летию со дня рождения его директора академика Льва Владимировича Таусона, руководившего институтом в период с 1961 по 1989 гг. На конференции были представлены результаты исследований, которые связаны с широким кругом вопросов современной геохимии, включая следующие направления: «Изотопно-геохимические исследования магматических, метаморфических и осадочных комплексов пород различных геодинамических обстановок»; «Геохимические исследования рудно-магматических систем и современные методы поисков и прогнозирования месторождений полезных ископаемых»; «Геохимия окружающей среды, геоэкология и палеоклимат»; «Экспериментальное и физико-химическое моделирование природных и техногенных процессов, физическое материаловедение»; «Современные аналитические методы исследований и информационные технологии в науках о Земле». В вводной статье показана неразрывная связь творческого пути Льва Владимировича с развитием Института геохимии СО РАН и приведен обзор материалов, представленных на конференции и затрагивющих ряд проблем формирования геологических комплексов разной природы, включая оценку источников вещества, геодинамических условий их проявления и характеристику рудообразующих процессов On 21–25 November, 2022, Vinogradov Institute of Geochemistry, Siberian Branch of the Russian Academy of Sciences (Irkutsk), organized an All-Russian anniversary conference celebrating 65 years to the date of the Institute foundation and 105 years to the birth of its first director, Lev Vladimirovich Tauson, Full Member of the Russian Academy of Sciences. The results reported at the conference encompass a wide range of research fields in modern geochemistry, including isotope geochemistry of igneous, metamorphic, and sedimentary rocks in various geodynamic settings; chemistry of ore-magmatic systems and modern methods of mineral exploration; environmental geochemistry, geoecology, and paleoclimate; laboratory modeling and thermodynamic calculations of natural and production-related processes and materials; advanced analytical methods and information technologies for geosciences. The conference presentations pay tribute to Lev Tauson whose academic carrier, as well as all creative activity, had been closely related with the development of the Institute of Geochemistry. The preface paper provides a review of topics discussed at the conference concerning various geodynamic and geochemical problems, including sources of material, petrogenesis, and metallogeny.

To investigate the process and chemistry of mineral reaction zone formation, we conducted detailed petrographic observations and chemical analysis of rocks and minerals of spinel lherzolite xenoliths from basanites of Tumusun volcano (Baikal Rift Zone). The reaction zones gradually disappear from contact toward the center of the xenoliths. The influence of basanite melt on major and trace element composition of secondary minerals of reaction zones is notable only at a distance up to 100–200 μm from the contact. At a distance of 0.3–1.0 mm from the contact, the major and trace composition of secondary clinopyroxenes from the orthopyroxene reaction zone indicates their formation from a melt formed by dissolution of orthopyroxene and influenced by the element diffusion from basanite melt. Inside xenoliths, the secondary minerals have Mg# values equal to or higher than Mg# of primary minerals, and secondary clinopyroxenes inherit their depleted or enriched REE pattern from primary pyroxenes. The compositional variations in secondary clinopyroxenes testify melt heterogeneity. Clinopyroxene rims have slightly higher LILE and similar abundances of other trace elements compared to clinopyroxene cores. This is consistent with the model developed from experimental studies: due to the interaction with basanite, incongruent dissolution of orthopyroxene occurs to form a melt which circulates in lherzolite and leads to pyroxenes and spinel dissolution. Diffusion of elements from basanite results in lherzolite enrichment in K, Na, Rb, Ba, La, and Ce, which are incorporated in feldspars and clinopyroxene of reaction zones as well as in feldspar veinlets. Non-dissolved mineral cores are homogenous and similar in major and trace element composition to primary minerals without reaction rims.

The isotopic data showed that there are two stages distinguished in the Cenozoic history of the Darkhad depression volcanic activity, the Late Oligocene initial stage (~28.0–26.6 Ma) and the final Late Miocene – Early Pliocene stage (~5.8–4.2 Ma). It has been stated that the rocks of the initial stage are only represented by trachybasalts; however, among the final-stage basaltoids there are series of shield-volcano hawaite-basanite-phonotephrite rocks and compex trachybasaltic "valley" lava flows, the formation of which is the last stage in the territorial volcanic evolution. It has been shown that the initial-stage trachybasaltic andesites are characterized by their enrichment of TiO 2 , P 2 O 5 , Sr, Zn, Ga and low concentrations of Al 2 O 3 , MnO, CaO, Sc and HREE (La/Yb=27.2–30.2). Basaltoids of the final stage have a similar rare-element distribution and show an increase in the contents of TiO 2 , Al 2 O 3 , P 2 O 5 , LILE, HFSE, Th, U and in the degree of fractionation of REE (La/Yb from 12.2 to 20.9) towards the rocks alkalinity enhancement. Modeling of eclogite, pyroxenite and peridotite melting processes in the La/Yb – Sm/Yb system shows that trachybasaltic andesite melts could be formed at ~7–8 % melting of eclogitic matter or at ~10–11 % melting of Grt-containing pyroxenites, with trachybasalt formed at ~3 % melting of Grt-containing peridotites. The composition distribution of rocks in coordinates (Mg# – Fe/Mn) indicates that the parental magmas are the initial-stage trachybasaltic andesite magmas as well as the Early Pliocene trachybasaltic "valley" lava flows. Sr, Nd, Pb isotope characteristics of the Darkhad depression basaltoids show significant shift of isotopic ratios in time towards the relatively enriched mantle as compared with the depleted MORB mantle. The initial formation of trachybasaltic andesite melts occurred in the Late Oligicene at the pre-rift stage of the territory development involving metasomatized mantle matter, with the pyroxenite or eclogite component contained in the magma formation source. The origin of trachybasalt magmas of the final stage is associated with the processes of decompression melting of peridotites in a weakly metasomatized lithospheric mantle at the rift stage of the Darkhad structure development.

The Malko-Petropavlovsk zone of transverse dislocations (MPZ) was formed on the extension of the deep Avachinsky transform fault in perpendicular relation to the subduction trench. It is a natural boundary between variously aged slabs in Kamchatka (103–105 Ma under Southern Kamchatka and 87–92 Ma under the Eastern volcanic belt). Monogenetic cinder cones in the MPZ are randomly distributed along these long-lived rupture zones. Here we present new geochemical and isotopic results of monogenetic volcanism in the MPZ. Based on whole rock and trace element geochemistry, Pb-Sr-Nd isotopic ratios of monogenetic cinder cone magmas were shown to tap the enriched mantle source (low 143Nd/144Nd isotopic ratios (0.512959–0.512999), and changed as 87Sr/86Sr (0.703356–0.703451) and 206Pb/204Pb (18.30–18.45), 208Pb/207Pb (38.00–38.12) isotopic ratios). High Nb/Yb and La/Yb ratios, without significant inputs of the slab's components (the lowest Ba, Th content), indicate decompression melting predominately. Calculations of the pressure (9–11 kbar) and temperature (1160–1240 °C) conditions using a glass thermobarometer suggest that magma of monogenetic cinder cones resided near the Moho boundary prior to eruption. This correlates with the crustal discontinuity under the MPZ according to geophysical observations (converted-wave seismic exploration and magnetotelluric sounding). The majority of well-preserved monogenetic cinder cones were formed in Holocene, after the last glaciation, but eruptions were not observed historically. This, however, suggests that similar eruptions in the MPZ may occur in the future. Given that the MPZ hosts major population centres of Kamchatka (Petropavlovsk, Elizovo, Vilyuchinks, and Paratunka: ~ 250,000 people or ~ 80% of the whole Kamchatkan population live in the major cities on the coastline of the MPZ), we highlight the urgent need to install a continuous monitoring system around the MPZ cones, geophysical investigation, and more serious attention from the local government and scientists. In particular, a detailed study of the MPZ regarding age, volume, and volcanic hazard assessment (pyroclastic vs extrusive) will help reduce potential risks of eruptions from monogenetic volcanoes for humans and infrastructures.

The article shows first results of the large pantelleritic dike swarm study. Dike swarm breaks through the Middle Paleozoic granites and has a length of up to 40 km with the general Northeastern extension. The swarm rocks composition corresponds to pantellerite trachytes (AGP ~ 1.1) and pantellerites (AGP ~ 1.3). Felsic feldspars and amphiboles (arfvedsonite and cataphorite) as the main phenocrysts, in the microlite paragenesis, represent the mineral composition and the presence of such rare minerals as lorenzenite, Ca-ancylite, catapleiite, monazite, enigmatite eudialite and titanium is noted, such a set of minerals corresponds to typical agpaitic rocks. The distribution of rare elements in the Tsagaan-Uul dike swarm rocks both in character and concentration level corresponds to the petrotype. The key difference is the presence of Nb–Ta anomaly in pantellerite trachytes and pantellerites, which may indicate the involvement of fluid in the formation of the swarm rocks.

Based on government statistical data ~80% of the local Kamchatkan population (~250 ka people) live in the major cities on the coastal line of Avacha Gulf . It is the main transport seaway to Kamchatka , and and important Asia - North America air transport corridor. The Avacha Gulf is located in the Malko-Petropavlovsk zone of transverse dislocations (MPZ) on the extension of deep transform fault on the boundary between various ly aged slabs. Most of monogenetic cinder cones chaotic distributed in relation to the trench and belong to the long-living rupture zones of MPZ. Some of the monogenetic volcanoes are parasitic cones on the slopes of Koryaksky and Avachinsky stratovolcanoes and related with their magma plumbing systems. We here present new results of the geochemical and isotopic stud ies of monogenetic volcanism in MPZ. Based on whole rock and trace element geochemistry, Sr-Nd-Pb isotopic ratios of monogenetic volcanism, ­­ magmas were shown to sample the enriched mantle source with dominance decompression melting without significant inputs of the slab`s components. Calculations of the P, T conditions suggest magma residence of monogenetic cinder cones on the Moho boundary. That correlates with the geophysical observation of crustal discontinuity under the MPZ. Monogenetic cinder cones have an active magma plumbing system because during the Holocene time were several periods of activations. Presented results show necessary install continuous monitoring of environment changing around the Avacha Gulf and more serious attention from government and science. A more detailed investigation of MPZ will help degrease potential risks of eruptions from monogenetic volcanoes for human and infrastructures.

The paper presents new data on mineralogy, geochemistry, and Sr-Nd-Pb isotope systematics of Late Cenozoic eruption products of Uguumur and Bod-Uul volcanoes in the Tesiingol field of Northern Mongolia, with implications for the magma generation conditions, magma sources, and geodynamic causes of volcanism. The lavas and pyroclastics of the two volcanic centers are composed of basanite, phonotephrite, basaltic trachyandesite, and trachyandesite, which enclose spinel and garnet peridotite and garnet-bearing pyroxenite xenoliths; megacrysts of Na-sanidine, Ca-Na pyroxene, ilmenite, and almandine-grossular-pyrope garnets; and carbonate phases. The rocks are enriched in LILE and HFSE, show strongly fractioned REE spectra, and are relatively depleted in U and Th. The low contents of U and Th in Late Cenozoic volcanics from Northern and Central Mongolia represent the composition of a magma source. The presence of carbonate phases in subliquidus minerals and mantle rocks indicates that carbon-bearing fluids were important agents in metasomatism of subcontinental lithospheric mantle. The silicate-carbonate melts were apparently released from eclogitizied slabs during the Paleo-Asian and Mongol-Okhotsk subduction. The parent alkali-basaltic magma may be derived as a result from partial melting of Grt-bearing pyroxenite or eclogite-like material or carobantized peridotite. The sources of alkali-basaltic magmas from the Northern and Central Mongolia plot different isotope trends corresponding to two different provinces. The isotope signatures of megacrysts are similar to those of studied volcanic centers rocks. The P-T conditions inferred for the crystallization of pyroxene and garnet megacrysts correspond to a depth range from the Grt-Sp phase transition to the lower crust. Late Cenozoic volcanism in Northern and Central Mongolia may be a response to stress propagation and gravity instability in the mantle associated with the India-Asia collision.

Статья посвящена исследованию генетических связей пород K-Na умеренно-щелочной серии, проявленной в строении вулканического центра Белоголовский расположенного в тыловой части Срединного хребта Камчатки.Дифференцированный ряд пород серии включает в себя трахибазальты, трахиандезиты, трахиты, комендитовые трахиты и комендиты.Проведение расчетов баланса масс и редкоэлементного моделирования показало, что кристаллизационная дифференциация является основным процессом эволюции расплавов изученного вулканического центра, при этом основным фракционирующим минералом является

The main subject of this article is research on the genetic relationships in the K–Na subalkaline series that occurs in the Belogolovsky volcanic center located in the back part of Sredinny Range. The differentiated rock series includes trachybasalts, trachyandesites, trachytes, comendite, trachytes, and comendites. Mass balance calculation and trace element modeling show that crystal fractionation is the main process in volcanic center evolution and the main fractionated mineral is feldspar. Trace element characteristics of rock-forming minerals (Fsp, Cpx, Bt, Ap, and Ol) obtained by LA–ICP–MS method allowed calculation of the “mineral/rock” partition coefficients for the Belogolovsky volcanic center genetic model representation to explain melt evolution. Genetic connections were established between trachyandesites, trachytes, comenditic trachytes and comendites, whereas no direct genetic connections between trachybasalts and trachyandesites were detected.

1. Objectives Within the Northern-Mongolian –Transbaikalian Rift system, bimodal volcanic associations with felsic agpaitic rocks are widespread, often accompanied by alkaline granites plutons. There are two segments in the Rift system structure –Northern-Mongolian with length of 600 km and Western-Transbaikalian with length of 800 km on latitude.

The paper presents newly acquired data on concentrations of major and trace elements and on Sr, Nd, and Pb isotope composition in Pliocene and Late Pleistocene–Holocene mafic volcanic rocks of the Uksichan volcanic center, one of the largest in the Sredinnyi Range of Kamchatka. Based on these data, the mafic Pliocene volcanics are thought to be produced by the melting of heterogenized mantle, which had been hybridized by subduction and asthenospheric processes. The behavior of HFSE and Pb isotopic systematics provide evidence of the melting of subducted sediment and origin of pyroxenite segregations in the peridotite matrix. The low ∆8/4Pb values of the Pliocene lavas of Uksichan shield volcano and in modern large volcanic centers in the Central Kamchatka Depression are correlated with the magmatic productivity, which indicates, when considered together with HFSE and HREE behavior, that the Pacific asthenosphere was involved in the magma-generating processes. The Late Pleistocene–Holocene basalt volcanism, which was distributed over the peripheries of the Pliocene shield edifice, developed in an extensional environment as a result of the melting of an enriched mantle source. The attenuation and then complete termination of volcanic activity in the Sredinnyi Range in the Late Pleistocene–Holocene were associated with an increase in the ∆8/4Pb of the mafic lavas, which indicates that the center of the activity of the oceanic asthenosphere shifted eastward toward the Central Kamchatka Depression. The influence of the oceanic asthenosphere on subduction-related magmatism is not unique for convergence zones and should be taken into consideration when models are constructed for the origin of juvenile continental crust.

Изучены изотопно-геохимические характеристики эоцен--олигоценовых магматических пород Западной Камчатки. Показано, что магматические породы эоценового (45-53 млн лет) кинкильского комплекса Западной Камчатки характеризуются геохимическими признаками надсубдукционного вулканизма. Их изотопный состав Sr, Nd и Pb, низкие концентрации HFSE и HREE относительно состава MORB предполагают формирование первичных расплавов из деплетированных или слабо обогащённых по изотопному составу источников мантийного клина, в разной степени контаминированных кварц-полевошпатовыми сиалическими осадками. С конца среднего эоцена на территории Западной Камчатки в условиях внутриплитной активизации проявился K-Na щёлочно-базальтовый магматизм (46-31 млн лет), геохимические характеристики которого сходны с E-MORB, а также ультракалиевый щёлочно-базальтовый магматизм, развитие которого продолжалось вплоть до раннего миоцена (35-17 млн лет). Геодинамическая природа позднепалеогенового щелочного магматизма предполагает реализацию процессов рассеянного рифтогенеза.

Цель исследования – сравнительный анализ вещественной эволюции, возраста и петрогенетических особенностей редкометальных Li-F-гранитов в различных зонах раннемезозойского ареала магматизма. Полученные новые геохимические данные свидетельствуют об отсутствии связи происхождения редкометальных Li-F-гранитов за счёт процессов магматической дифференциации палингенной грани- тоидной магмы, родоначальной для многофазного Бага-Хэнтэйского плутона. Редкометальные граниты в периферической зоне раннемезозойского ареала по сравнению с их аналогами в центральной части (Бага-Хэнтэй) в большей степени обогащены элементами Li, Rb, Sn, Ta, F, которые интенсивно накапливаются в процессе флюидно-магматической дифференциации. Это подтверждает большую перспективность рифтового обрамления батолитов в отношении генетической связи редкометального оруденения и магматизма. Геохимическая специфика гранитов Хэнтэйской интрузии в центральной части раннемезозойского ареала может указывать на их более глубинный источник, связанный с мантийным плюмом.

The authors studied the isotope-geochemical composition of the Eocene volcanic rocks from the Kinkilsk complex of Western Kamchatka. The peculiarities of the distribution of high field strength and heavy rare-earth elements and their ratio, as well as the isotopic composition of Sr, Nd and Pb suggest the formation of primary melts from depleted or poorly enriched in isotopic composition of the mantle wedge sources in different contaminated quartz-feldspathic sialic sediments. Two types of dependences of εNd in volcanic rocks of the complex on the degree of differentiation of rocks and inter-element relations are revealed. The first is associated with strong contamination of igneous melts with quartz-feldspathic sediments, the second relates to the fractionation of an isotopic (Nd)-enriched magmatic source with weak contamination of the melts with a crustal terrigenous material. The distribution of large-ion (LILE) elements is typical for sources of melts enriched with aqueous fluid and formed with the participation of a substance of a metasomatized mantle wedge.