Abstract We present new major and trace element, high-precision Sr–Nd–Pb (double spike), and O-isotope data for the whole range of rocks from the Holocene Tolbachik volcanic field in the Central Kamchatka Depression (CKD). The Tolbachik rocks range from high-Mg basalts to low-Mg basaltic trachyandesites. The rocks considered in this paper represent mostly Late Holocene eruptions (using tephrochronological dating), including historic ones in 1941, 1975–1976 and 2012–2013. Major compositional features of the Tolbachik volcanic rocks include the prolonged predominance of one erupted magma type, close association of middle-K primitive and high-K evolved rocks, large variations in incompatible element abundances and ratios but narrow range in isotopic composition. We quantify the conditions of the Tolbachik magma origin and evolution and revise previously proposed models. We conclude that all Tolbachik rocks are genetically related by crystal fractionation of medium-K primary magmas with only a small range in trace element and isotope composition. The primary Tolbachik magmas contain ~ 14 wt. of MgO and ~ 4 wt. of {H2O} and originated by partial melting (~ 6) of moderately depleted mantle peridotite with Indian-MORB-type isotopic composition at temperature of ~ 1250 °C and pressure of ~ 2 GPa. The melting of the mantle wedge was triggered by slab-derived hydrous melts formed at ~ 2.8 {GPa} and ~ 725 °C from a mixture of sediments and MORB- and Meiji-type altered oceanic crust. The primary magmas experienced a complex open-system evolution termed Recharge-Evacuation-Fractional Crystallization (REFC). First the original primary magmas underwent open-system crystal fractionation combined with periodic recharge of the magma chamber with more primitive magma, followed by mixing of both magma types, further fractionation and finally eruption. Evolved high-K basalts, which predominate in the Tolbachik field, and basaltic trachyandesites erupted in 2012–2013 approach steady-state {REFC} liquid compositions at different eruption or replenishment rates. Intermediate rocks, including high-K, high-Mg basalts, are formed by mixing of the evolved and primitive magmas. Evolution of Tolbachik magmas is associated with large fractionation between incompatible trace elements (e.g., Rb/Ba, La/Nb, Ba/Th) and is strongly controlled by the relative difference in partitioning between crystal and liquid phases. The Tolbachik volcanic field shows that open-system scenarios provide more plausible and precise descriptions of long-lived arc magmatic systems than simpler, but often geologically unrealistic, closed-system models.

Data on the geology, petrography, and geochemistry of Middle–Late-Pleistocene rocks from the Tolbachik volcanic massif (Kamchatka, Klyuchevskaya group of volcanoes) are presented and compared with rocks from the neighboring Mount Povorotnaya, Klyuchevskaya group basement, and Holocene–historical Tolbachik monogenetic cones. Two volcanic series of lavas, middle-K and high-K, are found in the Tolbachik massif. The results of our data analysis and computer modeling of crystallization at different P–T–H2O–fO2 conditions allow us to reconstruct the geochemical history of the massif. The Tolbachik volcanic massif started to form earlier than 86 ka based on K–Ar dating. During the formation of the pedestal and the lower parts of the stratovolcanoes, the middle-K melts, depleted relative to NMORB, fractionated in water-rich conditions (about 3 of H2O). At the Late Pleistocene–Holocene boundary, a large fissure zone was initiated and the geodynamical regime changed. Upwelling associated with intra-arc rifting generated melting from the same mantle source that produced magmas more enriched in incompatible trace elements and subduction components; these magmas are high-K, not depleted relative to N-MORB melts with island arc signatures and rift-like characteristics. The fissure opening caused degassing during magma ascent, and the high-K melts fractionated at anhydrous conditions. These high-K rocks contributed to the formation of the upper parts of stratovolcanoes. At the beginning of Holocene, the high-K rocks became prevalent and formed cinder cones and associated lava fields along the fissure zone. However, some features, including 1975–1976 Northern Breakthrough, are represented by middle-K high-Mg rocks, suggesting that both middle-K and high-K melts still exist in the Tolbachik system. Our results show that fractional crystallization at different water conditions and a variably depleted upper mantle source are responsible for all observed variations in rocks within the Tolbachik volcanic massif. Sr–Nd isotopes are consistent with 2–4 crustal assimilation during formation of the pedestal and stratovolcanoes, while the young lava fields do not show evidence of crustal assimilation. Major and trace element data coupled with K–Ar dating provide strong evidence that Mount Povorotnaya, located in 8 km northeast of Plosky Tolbachik, is an old block of the Tolbachik massif pedestal and for the moment it is the oldest (306 ka) known object in Klyuchevskaya group of volcanoes.

Abstract We report petrography, and bulk rock, mineral and glass analyses of eruptive products of the 2012–13 eruption of Tolbachik volcano, Central Kamchatka Depression, Russia. Magmas are shoshonitic in composition, with phenocrysts of olivine and plagioclase; clinopyroxene phenocrysts are scarce. Samples collected as bombs from the active vent, from liquid lava at the active lava front, and as naturally solidified “toothpaste” lava allow us to quantify changes in porosity and crystallinity that took place during 5.25 km of lava flow and during solidification. Olivine-hosted melt inclusions from rapidly-cooled, mm-size tephra have near-constant {H2O} contents (1.19 ± 0.1 wt) over a wide range of {CO2} contents (< 900 ppm), consistent with degassing. The groundmass glasses from tephras lie at the shallow end of this degassing trend with 0.3 wt {H2O} and 50 ppm CO2. The presence of small saturation, rather than shrinkage, bubbles testifies to volatile saturation at the time of entrapment. Calculated saturation pressures are 0.3 to 1.7 kbar, in agreement with the depths of earthquake swarms during November 2012 (0.6 to 7.5 km below the volcano). Melt inclusions from slowly-cooled and hot-collected lavas have {H2O} contents that are lower by an order of magnitude than tephras, despite comparable {CO2} contents. We ascribe this to diffusive {H2O} loss through olivine host crystals during cooling. The absence of shrinkage bubbles in the inclusions accounts for the lack of reduction in dissolved {CO2} (and S and Cl). Melt inclusions from tephras experienced < 3 wt post-entrapment crystallisation. Melt inclusion entrapment temperatures are around 1080 °C. Compared to magmas erupted elsewhere in the Kluchevskoy Group, the 2012–13 Tolbachik magmas appear to derive from an unusually H2O-poor and K2O-rich basaltic parent.

Abstract Aggregates and euhedral crystals of native gold were found in sublimates formed during New Tolbachik Fissure Eruption in 2012–2013 (NTFE). Gold-bearing sublimate samples were taken from a red-hot (690 °C) degassing fracture in the roof of an active lava tunnel 1.5 km from active Naboko cinder cone in May 2013. The gas condensate collected at 690 °C in this site contains 16 ppb Au, 190 ppb Ag and 1180 ppm Cu compared to 3 ppb Au, 39 ppb Ag and 9.7 ppm Cu in the condensate of pristine magmatic gas sampled at 1030 °C. The 690 °C volcanic gas is most likely a mix of magmatic gas and local snow buried under the lava flows as indicated by oxygen and hydrogen isotope compositions of the condensate. The lower-temperature gas enrichment in gold, copper and chlorine is resulted from evaporation of the 690 °C condensate during forced gas pumping at sampling. Native gold was also found in fumarolic encrustations collected from caverns in basalt lava flows with temperature up to 600 °C in June 2014, in a year after eruption finished. The native gold precipitation in newly formed Cu-rich sublimates together with the well known gold occurrences in cinder cones of 1975–1976 Large Tolbachik Fissure Eruption manifest a transport capability of oxidized volcanic gas.

Abstract Historical basaltic eruptions of Tolbachik volcano (Kamchatka) are of a medium to high potassic type. The potassic character of magmatism can be attributed to the influence of CO2–CO-rich fluid at or near the magma generation depths. Decarbonatization reactions in the mantle under Tolbachik producing a column of the carbonic fluids may be connected with the recent accretion of Kronotsky paleoarc with carbonates dragged under the mantle wedge. With thermodynamic modeling, we show that reduced carbonic fluid at fO2 < {NNO} may be a good carrier of nickel transported in the form of Ni(CO)4. This carbonyl is expected to become thermally stable near the magmatic temperatures at pressures above 1 GPa. In the crust, it is predicted to be thermally stable within the {PT} field of the amphibolite facies. We connect the particles of native Ni and Ag–Pt alloy observed in the volcanic aerosols from the 2012–13 Tolbachik eruption with flushing of the ascending Tolbachik magma with reduced carbonic fluids enriched with {PGE} and Ni. Native metals may form by the thermal decomposition of the carbonyls and other carbon-bearing compounds dissolved in the fluid.

A numerical model is proposed for the mechanism of a rockslide avalanche on the slope of Koryakskiy volcano caused by the emplacement of sheeted intrusive bodies. The model of non-stationary geomechanical processes with abnormally low internal friction is used to calculate an avalanchelike movement during a potential collapse of the cone.

This study presents new geochemical data for Mutnovsky Volcano, located on the volcanic front of the southern portion of the Kamchatka arc. Field relationships show that Mutnovsky Volcano is comprised of four distinct stratocones, which have grown over that past 80 ka. The youngest center, Mutnovsky IV, has produced basalts and basaltic andesites only. The three older centers (Mutnovsky I, II, III) are dominated by basalt and basaltic andesite (60–80 by volume), but each has also produced small volumes of andesite and dacite. Across centers of all ages, Mutnovsky lavas define a tholeiitic igneous series, from 48–70 SiO2. Basalts and basaltic andesites have relatively low K2O and Na2O, and high FeO* and Al2O3 compared to volcanic rocks throughout Kamchatka. The mafic lavas are also depleted in the light rare earth elements (REEs), with chondrite-normalized La/Sm < 1.0. Andesites have generally higher REE abundances and are more enriched in light REEs, some showing negative Eu anomalies. All samples are depleted in field strength elements (HFSEs) relative to similarly incompatible REEs (e.g., low La/Ta, Nd/Hf compared to MORB), similar to island arc volcanic rocks worldwide. Radiogenic isotope ratios (Sr, Nd, Pb, Hf) are similar for samples from all four eruptive centers, and indicate that all samples were produced by melting of a similar source mixture. No clear age-progressive changes are evident in the compositions of Mutnovsky lavas. Mass balance and assimilation-fractional crystallization (AFC) modeling of major and rare earth elements (REEs) indicate that basaltic andesites were produced by FC of plagioclase, clinopyroxene and olivine from a parental basalt, combined with assimilation of a melt composition similar to dacite lavas present at Mutnovsky. This modeling also indicates that andesites were produced by FC of plagioclase from basaltic andesite, combined with assimilation of dacite. Dacites erupted from Mutnovsky I and II have low abundances of REEs, and do not appear to be related to mafic magmas by FC or AFC processes. These dacites are modeled as the products of dehydration partial melting at mid-crustal levels of a garnet-free, amphibole-bearing basaltic rock, which itself formed in the mid-crust by emplacement of magma that originated from the same source as all Mutnovsky magmas. Lead isotope data indicate that subducted sediment is likely present in the source beneath Mutnovsky and most Kamchatka volcanoes, but uniformly radiogenic Hf and Nd in mafic samples (εNd = 8.7–9.3, εHf = 15.4–15.9), and significant variation in trace element ratios at nearly constant εNd and εHf, indicate that sediment plays a minor roll in controlling subduction trace element patterns in Mutnovsky lavas. Mafic lavas with Ba/Th > 450 require an aqueous fluid source component from subducting oceanic crust, but mixing patterns in isotope versus trace element ratio plots for Hf and the REEs (εNd and εHf vs. ratios with Ce, Nd and Hf) demonstrate that a source component with radiogenic Nd and Hf, and fractionated (arc-type) trace element ratios must be present in the source of Mutnovsky lavas. This source component, which is interpreted to be a partial melt of subducted basalt in the eclogite facies (eclogite melt source component), appears to be present in the source of all Kamchatka volcanoes. Cross-arc geochemical patterns at Mutnovsky and in other arc systems (Isu-Bonin, Tonga-Kermadec) suggest that the aqueous fluid component diminishes and the eclogite melt component is increased from volcanoes at the arc front compared to those in rear-arc positions.

Avacha group includes two active and potentially dangerous volcanoes, Avachinsky and Koryaksky, located close to Petropavlovsk-Kamchatsky, the main city of Kamchatka. We present the results of two independent seismic studies of shallow crustal structures beneath the Avacha group based on passive and active source observations. The first study is based on the analysis of continuous recording by 11 seismic stations installed over the Avacha group in 2012 and 7 permanent stations in the same region. We present a series of 2D Rayleigh-wave group velocity maps based on correlation of ambient noise, that were then converted into 3D distribution of shear wave velocity. The second work was based on the reprocessing of an active source deep seismic sounding profile across the Avachinsky volcano that was shot in 1982–1984. We made the analysis of travel times of refracted waves using a 2D tomography inversion. The resulting seismic models appear to be consistent with each other and show clear low-velocity zone to the SW of the Avachinsky volcano and high velocity structures to NE. These observations also agree with the existing gravity and magnetotelluric measurements. Based on the obtained seismic models we identify two large buried calderas and large lava flows that are thought to be related to a series of large eruption episodes of Avachinsky occurred within the last 30,000 years.

Abstract Gases and aerosols from the 2012–13 effusive eruption of Tolbachik basaltic volcano, Kamchatka, were sampled in February and May, 2013, from a lava tube window located 300 m from the eruptive crater; temperature at the sampling point was 1060–1070 °C. The chemical and isotopic compositions of the sampled gases (92.4 H2O, 3.5 CO2, 2.3 SO2 on average; δD from − 25.0 to − 38.6‰) correspond to a typical volcanic arc gas without dilution by meteoric or hydrothermal water. Halogen contents in the gases (1.37 HCl, 0.5 HF) were higher than average arc values. The total amount of analyzed metallic and metalloid (trace) elements in the gas exceeded 665 ppm. Six most abundant trace elements, K (250 ppm), Na (220 ppm), Si (74 ppm), Br (48 ppm), Cu (21 ppm) and Fe (12 ppm), accounted for 95 of the total content of trace elements in the gas. The gases contained 24 ppb Re, 12 ppb Ag, 4.9 ppb Au and 0.45 ppb Pt. Refractory rock-forming elements (Mg, Al, Ca) and some other elements such as Ba and Th were transported mainly in the form of silicate microspheres and altered rock particles. The concentrations of metals in the eruptive Tolbachik gases are higher than the corresponding concentrations in high-temperature fumaroles worldwide, although the mutual ratios of the elements are approximately the same. The gas/magma partition coefficients of eleven elements exceed unity, including the non-metals F, S, Cl, Br, As, Se and Te and the rare metals Cd, Re, Tl and Bi. Despite the relatively low concentrations of trace elements in the volcanic gases at the highest temperatures, superficial magma degassing provides information on the sources and sinks of metals.