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C ages constrain voluminous mafic volcanism of the Kamchatka back-arc to Miocene (3–6 Ma) and Late Pleistocene to Holocene (<1 Ma) times. Trace elements and isotopic ...compositions show that older rocks derived from a depleted mantle through subduction fluid-flux melting (>20%). Younger rocks form in a back arc by lower melting degrees involving enriched mantle components. The arc front and Central Kamchatka Depression are also underlain by plateau lavas and shield volcanoes of Late Pleistocene age. The focus of these voluminous eruptions thus migrated in time and may be the result of a high fluid flux in a setting where the Emperor seamount subducts and the slab steepens during rollback during terrain accretions. The northern termination of Holocene volcanism locates the edge of the subducting Pacific plate below Kamchatka, a “slab-edge-effect” is not observed in the back arc region.
Clusters of small-volume volcanoes that individually may be defined as monogenetic, but have interlinked and interconnected plumbing systems, are used to be categorized as monogenetic volcanic fields ...(MVF). We argue that such volcanic clusters should be distinguished as separate type of volcanism, intermediate between monogenetic and polygenetic. The magma plumbing system structure of the MVF (its complexity and polymagmatic character) is the key argument for the potential separation of them in a classification. To avoid confusion caused by genetic meaning of the used words we suggest using a term “areal volcanism” or “areal volcanic fields” (AVF instead of MVF) as defining this special type of volcanic activity. Here we provide a review of the main characteristic features of one of the largest Holocene AVF, which is active now – the Tolbachik field of cinder cones in the southern part of Klyuchevskaya volcano group (Kamchatka), known in the literature as Tolbachinsky Dol. This paper is focused on the research of magma plumbing system. We consider structural, morphological, geological, geochemical and petrological data on the erupted basalts and their genesis. Specially planned seismic experiments made in 2010–2015 (seismic tomography and microseismic sounding) allowed modeling of the principal elements of the magma plumbing system of Tolbachik AVF. Analysis of the investigations made in this area shows that Tolbachik AVF has a complex, dynamic, variable magmatic feeding system, which can be visualized as a superposition of subvertical and sublateral magma conduits. The contrast composition of the erupted rocks is caused by their different, although genetically connected, magma sources and mixing processes. One of the long-lived eruptive centers of Tolbachik AVF is Plosky Tolbachik stratovolcano, which lost its independent activity and was captured by Tolbachik AVF in Holocene. The AVF formed rejuvenated volcanism using the feeding system of the stratovolcano like an “old anthill”. The magma plumbing system characteristics of Tolbachinsky Dol strongly support the idea of separation of AVF from monogenetic volcanism type in the classification.
•We combine petrological and geophysical data to study Tolbachik areal volcanic field.•We discuss features of magma supply of Tolbachik historical fissure eruptions.•We show integrated models of magma plumbing system for Tolbachik areal volcanic field.•We argue for classification of areal volcanic fields as separate type of volcanism.
We present a reconstruction of the chronological sequence of events that took place during the first days of the 2012–2013 Tolbachik fissure eruption using petrological data and remote sensing ...methods. We were forced to use this approach because bad weather conditions did not allow direct observations during the first two days of the eruption. We interpreted infrared images from the scanning radiometer VIIRS Suomi NPP and correlated the output with the results of the geochemical study, including comparison of the ash, deposited at the period from 27 to 29 November, with the samples of lava and bombs erupted from the Menyailov and Naboko vents. We argue that the compositional change observed in the eruption products (the decrease of SiO2 concentration and K2O/MgO ratio, increase of MgO concentration and Mg#) started approximately 24h after the eruption began. At this time the center of activity moved to the southern part of the fissure, where the Naboko group of vents was formed; therefore, this timeframe also characterizes the timing of the Naboko vent opening. The Naboko group of vents remained active until the end of eruption in September 2013.
•We describe the initial period of eruption using petrological and satellite data.•Compositions of distal ash deposits and lava are compared.•Time frames of the onset of activity at Naboko group of vents are determined.
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.
•The first regional-scale compositional dataset for rocks from the Kamchatka back-arc.•143Nd/144Nd and HFSE indicate the presence of enriched mantle under the region.•Delamination of the metasomatized lithosphere explains the enrichment.•143Nd/144Nd is the best indicator of the variable age of the delaminating lithosphere.
We present a broad overview of the 2012–13 flank fissure eruption of Plosky Tolbachik Volcano in the central Kamchatka Peninsula. The eruption lasted more than nine months and produced approximately ...0.55km3 DRE (volume recalculated to a density of 2.8g/cm3) of basaltic trachyandesite magma. The 2012–13 eruption of Tolbachik is one of the most voluminous historical eruptions of mafic magma at subduction related volcanoes globally, and it is the second largest at Kamchatka. The eruption was preceded by five months of elevated seismicity and ground inflation, both of which peaked a day before the eruption commenced on 27 November 2012. The batch of high-Al magma ascended from depths of 5–10km; its apical part contained 54–55wt.% SiO2, and the main body 52–53wt.% SiO2. The eruption started by the opening of a 6km-long radial fissure on the southwestern slope of the volcano that fed multi-vent phreatomagmatic and magmatic explosive activity, as well as intensive effusion of lava with an initial discharge of >440m3/s. After 10days the eruption continued only at the lower part of the fissure, where explosive and effusive activity of Hawaiian–Strombolian type occurred from a lava pond in the crater of the main growing scoria cone. The discharge rate for the nine month long, effusion-dominated eruption gradually declined from 140 to 18m3/s and formed a compound lava field with a total area of ~36km2; the effusive activity evolved from high-discharge channel-fed 'a'a lavas to dominantly low-discharge tube-fed pahoehoe lavas. On 23 August, the effusion of lava ceased and the intra-crater lava pond drained. Weak Strombolian-type explosions continued for several more days on the crater bottom until the end of the eruption around 5 September 2013. Based on a broad array of new data collected during this eruption, we develop a model for the magma storage and transport system of Plosky Tolbachik that links the storage zones of the two main genetically related magma types of the volcano (high-Al and high-Mg basalts) with the clusters of local seismicity. The model explains why precursory seismicity and dynamics of the 2012–13 eruption was drastically different from those of the previous eruption of the volcano in 1975–76.
•The 2012–13 eruption of Tolbachik produced 0.55km3 DRE of basaltic trachyandesite magma.•The 2012–13 eruption is one of the most voluminous historical eruptions of mafic magma at subduction-related volcanoes.•Data on the 2012–13 eruption precursors and dynamics are summarized.•Model for the magma storage and transport system of Tolbachik is presented.•Differences of precursory seismicity associated with eruptions of the high-Al and high-Mg magmas are explained.
We report, here, the composition and KAr ages of a representative collection of volcanic rocks that erupted within three monogenetic volcanic fields in the active fault zone of the Sredinny Range of ...Kamchatka: Tigilsky Dol, Mount Oxi massif and Anaunsky Dol. The studied rocks display a wide range of compositions (medium-K, moderate-Mg, high-K, high-Ti and high-Mg basalts, and high-LREE picrobasalts); the high-Mg varieties are confined to faults. Five main periods of volcanic activity were investigated, 4.3–3, 2, 1.5, 1 Ma and from 0.3 to <0.05 Ma. Primitive lavas first emerged on the surface at 3.5 Ma. There was a massive outpouring of high-Mg lavas at 1.5–1 and 0.3 Ma, which could have been related to the formation of the fault zone. This is the first report of rocks in Kamchatka with a high-LREE picrobasaltic composition (1.5 Ma). The Fo content of the olivine phenocrysts reaches 93.2 mol%, which is the highest value known for Quaternary Kamchatka basalts. A very heterogeneous source, even for individual eruptions is indicated by the minor element contents in the olivine (Ni, Mn and Ca); Cr-spinel – olivine paragenesis show that all the rocks studied crystallized in the same temperature range (1111–1292 °C), whereas the oxygen fugacity for the different samples varied from ΔQFM +0.7 to +2.0 log. units. A melt inclusion study showed that the Mg basalts of the Mt. Oxi massif and the high-LREE picrobasalts of Tigilsky Dol had different fluid sources that were enriched and depleted in water and Cl, respectively. We argue that the fluid source for the Mt. Oxi massif was likely the remains of the Pacific slab under the Sredinny Range, whereas, for the high-LREE picrobasalts of Tigilsky Dol, it was the lithospheric lithologies. The low content of S and high content of Cu in the oxidized high-LREE basalts provide additional evidence that they originated from the re-melting of sulfur-poor lithospheric lithologies. Both the fault zone and the lithosphere re-activation in the region are likely linked to the regional stress field.
•Monogenetic volcanic fields found in an active fault zone (Sredinny Range, Kamchatka).•An unusual compositional variety of volcanic rocks erupted along an active fault zone.•High-Mg rocks have been common in the studied area for at least 1.5 Ma.•The Sredinny Range is host to compositionally very unusual high-LREE picrobasalts.•Crystallization was controlled by T, fO2 and the H2O, Cl, F, S contents of the magmas.
Here we present the results from monitoring of the composition of rocks produced during the 2012–2013 fissure eruption at Tolbachik volcano (FTE). Major and trace element concentrations in 75 samples ...are reported. Products of this eruption are represented by high alumina basaltic trachyandesites with higher alkalis and titanium contents than in all previously studied rocks of the Tolbachik monogenetic volcanic field. Rocks erupted during the first three days (27–30 November) from the northern (also called Menyailov) group of vents are the most silica- and alkali-rich (SiO2 concentrations up to 55.35wt.% and K2O up to 2.67wt.%). From December onwards, when the eruptive activity switched from the Menyailov vents to the southern (Naboko) group of vents, silica content dropped by 2wt.%, concentrations of MgO, FeO, TiO2 and Mg# increased, and K2O and Na2O concentrations and K2O/MgO ratio decreased. For the rest of the eruption the compositions of rocks remained constant and homogeneous; no systematic compositional differences between lava, bombs and scoria samples are evident. Trace element distributions in the rocks of the Menyailov and Naboko vent lavas are relatively uniform; Menyailov lavas have slightly higher Th, Nb, Hf, Y, and HREE concentrations than the Naboko vent lavas at more or less constant element ratios. We explain the initial change in geochemistry by tapping of a slightly cooler and fractionated (~3% Mt and 8% Cpx) upper part of the magma storage zone before the main storage area began to feed the eruption. Thermodynamic constraints show that apparent liquidus temperatures varied from 1142°C to 1151°C, and thermodynamic modeling shows that variations in compositions are consistent with a high degree of low pressure (100–300MPa), nominally anhydrous fractionation of a parent melt compositionally similar to the 1975 Northern Breakthrough high-Mg basalt. Geochemistry, petrological observations and modeling are in agreement with the newly erupted material being derived from remnant high-Al magma from the 1975–76 Southern Breakthrough eruption with only slight amounts of cooling (less than 1°C per year) during the intervening 36years.
•We present a set of lava compositions spanning the 2012–13 Tolbachik fissure eruption.•We document a major compositional change after the first three days of eruption.•From the mid December until the end of eruption lava compositions remained constant.•High alumina basaltic trachyandesites with high alkalis and Ti content were erupted.•Petrological modeling shows that high-Al 1975–6 and new lavas are genetically related.
The Kamchatka volcanic arc (Russia) is one of best-studied, but most complex tectonic margins on Earth, with an extensive geologic history extending back to the Late Cretaceous. Unlike many other ...subduction zones, primitive basalts with Mg# > 65 are abundant in Kamchatka, thereby allowing characterization of the mantle source through compositional analyses of near-liquidus minerals in the rocks. In this paper, we present a comprehensive dataset on the composition of Cr-spinel inclusions in olivine for all main Late Quaternary volcanic zones in Kamchatka, comprising 1604 analyses of spinel inclusions and their host-olivine in 104 samples from 30 volcanic complexes (single volcanoes and volcanic fields). The studied rocks are basalts, basaltic andesites and high-Mg andesites, which cover the whole compositional range of the primitive Late Quaternary volcanic rocks in Kamchatka. The spinel composition shows large variability. Spinel inclusions with the lowest Cr# and Fe3+/Fe2+ ratios were found in basalts from Sredinny Range and Northern Kamchatka, whereas the most Cr-rich and oxidized spinel inclusions occur in basalts and high-Mg andesites from the Central Kamchatka Depression. Intermediate Cr-spinel compositions characterize the Eastern Volcanic Belt of Kamchatka. The compositions of olivine-spinel pairs were used to quantify the oxidation state of parental Kamchatka magmas and the degree of partial mantle melting. The redox conditions recorded in spinel compositions range from ΔQFM = +0.7 to +3.7. ΔQFM for spinel from the Sredinny Range and Northern Kamchatka correlates with a number of whole-rock proxies for the involvement of slab-derived components (e.g., La/Nb and Ba/La), which suggests a coupling between mantle oxidation state and slab-derived fluid/melt metasomatism. These correlations were not observed in frontal Kamchatka volcanoes with the highest estimated ΔQFM, which possibly indicates buffering of the mantle oxidation state by sulfur. The estimated degrees of partial mantle melting range from 8 to >20% for Kamchatka volcanoes. Spinel from the Central Kamchatka Depression has the highest Cr# and could crystallize from magmas generated from the most depleted sources. In contrast to the Eastern Volcanic Belt, spinel Cr# and the inferred degrees of melting in the Central Kamchatka Depression do not correlate with spinel TiO2 content. The apparent decoupling between the proxies of mantle depletion in the CKD spinel is interpreted to reflect refertilization of the CKD mantle by oxidized Ti-rich slab- or mantle lithosphere-derived melts near the northern edge of the subducting Pacific Plate. This study demonstrates that the composition of Cr-spinel in volcanic rocks in combination with bulk-rock compositions can be a powerful tool to map regional variations of the mantle source depletion, oxidation state, and involvement of various slab-derived components in island-arc magmatism.
•First comprehensive dataset of spinel inclusions in high-Mg olivine from Kamchatka•Oxidation state of parental magmas of Kamchatka ranging from ΔQFM+0.7 to +3.7•ΔQFM correlates with Ba/La and La/Nb for back-arc magmas of Kamchatka•Decoupling of Cr# and TiO2 in primitive Cr-Spinel suggests slab melt contribution
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