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Program of basic research of the Presidium of Russian Academy of Sciences #15 "The natural catastrophes and adaptive processes under the conditions of climate changing and development of nuclear power engineering".

  • V. A. LebedevV. A. Lebedev
  • I.V.Chernyshev
  • Yu.V.Gol'tsman

Goal: Project: "The geochronology and peculiarities of evolution of young catastrophic volcanism in the Northern Eurasia: evidence from the isotope studies"
The study of chronology and periodicity of Neogene-Quaternary volcanism in the Northern Eurasia (the territory of Russia and adjacent countries), the obtaining of isotope-geochemical data for determination of petrogenesis of young volcanic rocks, the formulation of criterias for long-term forecast of the possibility for resumption of catastrophic volcanic eruptions in the future within the concrete regions.

Methods: Mineralogy, Petrology, Volcanology, Microscope, Isotope Geochemistry, Geochronology, Satellite Image Analysis, Geoecology, Geological Mapping

Date: 1 January 2015 - 31 December 2017

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V. A. Lebedev
added a research item
The paper presents the results of isotope-geochronological and petrological-geochemical study of young volcanic rocks in the Geghama highland (Central Armenia), which were formed at the Pliocene–Early Quaternary stage of the Late Cenozoic post-collisional magmatism of the Lesser Caucasus. The boundaries of the area of volcanic activity manifested during this stage were established. The total duration (3.5–1.9 Ma) of the Pliocene–Early Quaternary stage, the time range of its main phases, and the scale and nature of eruptions were determined. Petrological and geochemical data indicate that the studied young volcanic rocks from Central Armenia belong to the mildly alkaline series and are represented by a continuous association of (trachy-)basalt–mugearite–latite–trachyte–rhyolite. The geochemical evolution of parental basaltic melts was mainly controlled by the fractional crystallization with Cpx as the main cumulus phase. Crustal assimilation and mixing of magmas were of limited importance: their possible contribution was recorded only in the most silicic rocks. The deep source responsible for magma generation under the studied part of the Lesser Caucasus at the Pliocene–Pleistocene boundary was represented by the asthenospheric mantle that was enriched during previous long-term (tens of millions of years) subduction of the Neotethys slab. Melting occurred in the Grt-peridotite stability zone; the composition of derived melts was geochemically similar to E-MORB basalts. An important feature of the regional mantle source was the notable admixture of subduction component. The generalization of the obtained petrological–geochemical and isotope–geochemical data on the young igneous rocks formed at different stages of Late Cenozoic magmatism at the Geghama highland allowed us to trace the evolution of the main parameters (mineral, chemical, and isotopic composition, depth of location, degree of melting) of mantle reservoirs responsible for magma generation beneath Central Armenia at the post-collisional stage (from the Late Miocene to the Holocene). Russian version of the paper here (русская версия статьи по ссылке) https://www.researchgate.net/publication/353484253_Pliocenovyj_postkollizionnyj_vulkanizm_Centralnoj_Armenii_izotopnaa_geohronologia_i_zakonomernosti_geohimiceskoj_evolucii_rasplavov
V. A. Lebedev
added a research item
The results of petrological-geochemical and isotope-geochemical studies of the Late Pleistocene-Holocene lavas of the Kazbek neovolcanic center, one of the largest centers of youngest magmatism in the Greater Caucasus, are presented. It has been established that the volcanic rocks of the Kazbek center form a continuous compositional series basaltic (trachy-)andesites-(trachy-)andesites-dacites with a predominance of calc-alkaline intermediate and moderately-acid lavas. The obtained results indicate that fractional crystallization and mixing of melts had a leading role in the petrogenesis of the rocks. The crustal assimilation was of limited importance; its influence is noticeable only in the rocks of the earliest and late pulses of mag-matic activity within the Kazbek center. The common crustal lithologies participating in the assimilation were metamorphosed Jurassic sediments (mainly shales and sandstones) forming the base of the Kazbek center and rarely Mesozoic mafic metamorphosed volcanites. The specific features of AFC processes during the development of the studied magmatic system (including the presence of noticeable amount of water in the melt, the leading role of Amp in the cumulus and the absence of Pl fractionation) led to the appearance of dacitic lavas with geochemical signs of adakites as an evolutional end-member. The volcanic rocks of the Kaz-bek center are derived from trachybasalt magmas, the source of which was presented by the mantle reservoir of OIB-type. Recent and previously published results of studies of the Neogene-Quaternary magmatism manifested within the Greater Caucasus show that the main petrological and geochemical characteristics of this regional mantle reservoir remained constant from the end of the Miocene to the present time.
V. A. Lebedev
added a research item
The paper reports the isotope-geochronological and petrological-geochemical studies of the Pliocene moderately-acid volcanism of the Akhalkalaki Plateau in the central part of the Lesser Caucasus (Javakheti highland, Georgia). K-Ar dating showed that young dacitic lavas and pyroclastic rocks were formed in the mid-Pliocene (3.28 ± 0.10 Ma) in relation with the explosive–effusive eruptions of small composite volcanic cones and formation of minor extrusive domes confined mainly to the eastern margin of the region. Isotope-geochronological data in the combination with results of structural drilling indicate that the considered short-term pulse of the volcanic activity occurred during a short gap between two phases of the Pliocene–Early Pleistocene mafic magmatism widespread within the Akhalkalaki plateau. The studied Pliocene dacites were erupted at the post-collisional stage of the evolution of the Lesser Caucasus, but bear petrological- geochemical affinity of adakitic series. They are characterized by the steady presence of amphibole phenocrysts, the elevated contents of Sr, Ba, LILE and the lowered contents of Y, Nb, Ta, and HREE, and have depleted Sr isotopic composition (87Sr/86Sr < 0.7045). Analysis of petrogenetic models earlier proposed to explain the generation of adakite-like magmas in the modern collision zones showed that the origin of the Pliocene dacitic lavas of the Akhlkalaki plateau is best described by the crystallization differentiation of watersaturated calc-alkaline basaltic melts with removal of common mafic rock-forming minerals (first of all, amphibole and pyroxene) and accessory phases (apatite, titanite, Ti-magnetite) as cumulus minerals. Crustal assimilation of evolved magmas only insignificantly contributed to the petrogenesis of the dacites.
V. A. Lebedev
added a research item
This paper is aimed at studying the chronological evolution of the Neogene–Quaternary volcanic activity within the Çaldıran plain and its mountainous framing (Eastern Turkey). It is shown that the last pulse of continental-margin magmatism related to the subduction and closure of Neotethys oceanic basin occurred in the Middle Miocene (13.5–12.5 Ma). The post-collision volcanism proceeding simultaneously with large-scale regional tectonic rearrangement and initiation of the long-term Çaldıran fault began in the Late Miocene (7–6 Ma), and reached maximum activity in the Middle Pliocene (4.7–3.6 Ma). The Quaternary period in the region evolution was marked by the abundant within-plate magmatic activity restricted to the regional SW–NE trending zone, and the formation of Eastern Turkey’s largest Tendürek shield volcano (Late Pleistocene–Holocene). Petrological-geochemical data indicate that magmas during the overall evolution of young volcanism of the Çaldıran plain was generated from a single mantle reservoir, whose composition gently one-way evolved with time. Calculations show that melting occurred in the upper part of the asthenosphere (immediately near the boundary with thinned lithospheric mantle), which was metasomatized by pre-existing long-continued subduction. The chemical variations of mantle source with time (from the Middle Miocene to Quaternary) were mainly determined by a decrease of subduction component and the presence of aqueous phases, with a general trend from E-MORB to OIB-type for generated magmas. The composition of Late Quaternary basic lavas of Tendürek Volcano in terms of most petrological-geochemical characteristics corresponds to within-plate alkaline basalts. The main trend of geochemical evolution of mantle source is correlated with a systematic change of the predominant serial affinity of igneous rocks from calcalkaline through moderately alkaline to Na-alkaline varieties. Discrete character of young magmatism within the Çaldıran plain, and its subsequent evolution (sulrasubduction → post-collision → within-plate) were mainly determined by periodical large-scale changes in geotectonic setting within the Eurasian–Arabian collision zone: (1) cessation of subduction, (2) break-up and deepening of oceanic slab with its subsequent break off, (3) inferred emergence of incipient rift setting under conditions of intense submeridional compression.
V. A. Lebedev
added a research item
This paper presents the results from an isotope-geochronological and geochemical-petrological study of young volcanic rocks sampled in central Armenia, which were formed during the first stage of the Late Cenozoic magmatism in the Lesser Caucasus at the Miocene/Pliocene boundary. We have found the boundary of the area where the Miocene to Pliocene volcanism was evolving, determined its scale and total duration (~1Ma, between 5.7 and 4.7 Ma), and identified phases of magmatic activity: I during 5.56 ± 0.18, II during 5.39 ± 0.04, and III during 4.86 ± 0.20 Ma. Petrologic data show that the volcanic rocks of central Armenia studied here compose a continuous compositional series from potassium trachybasalt to mugearite to (trachy)andesite to trachyte to rhyolite, while the leading process in the petrogenesis of their parent magmas had been fractional crystallization during the entire period of magmatic activity from the Late Miocene to the Early Pliocene. Crustal assimilation was of limited importance: some small influence of this process was only found for some late lavas that were erupted during phase III. The geochemical evolution of lavas during the earlier phases of activity was occurring unidirectionally from basic to acid compositions; the resumed eruptions of trachyandesites and andesites during phase III after a long intermission was caused by replenishment of mantle melts into magma chambers beneath the region. The entire data set for the area of central Armenia was analyzed to identify one volcanic unit that includes all Miocene to Pliocene magmatic rocks that are found there. The mantle source that was responsible for melt generation beneath the better known area of the Lesser Caucasus during the time period of interest was an OIB-type asthenospheric mantle that had been metasomatized by the subduction of the oceanic lithosphere from the Neotethys Basin.
V. A. Lebedev
added a research item
Коллективная монография в иллюстрированной форме отражает результаты работ наших ученых, принимавших участие в выполнении проектов программы Президиума Российской академии наук «Природные катастрофы и адаптационные процессы в условиях изменяющегося климата и развития атомной энергетики».
V. A. Lebedev
added 3 research items
Supplement material to V. A. Lebedev, A. V. Parfenov, G. T. Vashakidze, Q. A. Gabarashvili, I. V. Chernyshev, and M. G. Togonidze "Chronology of Magmatic Activity and Petrologic–Mineralogical Characteristics of Lavas of Kazbek Quaternary Volcano, Greater Caucasus", Petrology, 2018, Vol. 26, No. 1, pp. 1–28.
Supplement material to V. A. Lebedev, A. V. Parfenov, G. T. Vashakidze, Q. A. Gabarashvili, I. V. Chernyshev, and M. G. Togonidze "Chronology of Magmatic Activity and Petrologic–Mineralogical Characteristics of Lavas of Kazbek Quaternary Volcano, Greater Caucasus", Petrology, 2018, Vol. 26, No. 1, pp. 1–28.
Supplement material to V. A. Lebedev, A. V. Parfenov, G. T. Vashakidze, Q. A. Gabarashvili, I. V. Chernyshev, and M. G. Togonidze "Chronology of Magmatic Activity and Petrologic–Mineralogical Characteristics of Lavas of Kazbek Quaternary Volcano, Greater Caucasus", Petrology, 2018, Vol. 26, No. 1, pp. 1–28.
V. A. Lebedev
added 53 research items
New potentialities of isotope geochronology including K-Ar-method make it possible to describe history of both individual volcanoes and large volcanic areas in period since early to the last stages of their development. Determination of potential volcanic hazard is possible. Investigations of known volcanic centers have been performed. Results of the investigation have led to determination of site of the last volcanism. Numerical time intervals of stages of its magmatic activity have been found. It has been shown that recommencing of volcanic activity is possible in the Caucasus region.
The K-Ar and Rb-Sr isotope-geochronological study for dacitic volcanites of Dzhavakheti highland (South Georgia) was carried out. The young magmatism developed here within last 7-8Ma. We distinguished three separate magmatic stages: 8-7Ma, 4-2Ma and 800ka – less 50ka. The volcanites of dacitic compound dominate in first and last magmatic stages. The pyroclastic rocks and dacitic lava flows of Goderdzi suite were erupted in Late Miocene. Volcano Amiranisgora and volcano Chikiani formed about 3Ma. Dacitic lavas of Dzhavakheti ridge were erupted in Late Pliocene. Dacitic volcanism of Samsari ridge has begun less 800ka. It includes four separate phases. The study of Sr-Nd isotope systematic for Samsari ridge quaternary volcanites shown that the mantle substance played a major part in rock genesis with negligible crustal contamination.
The isotope–geochronological data obtained reveal a large center of Late Quaternary volcanism in the southern part of Republic of Georgia – Samsari volcanic center, with its main development phases corresponding to phases of magmatic activity previously defined for other areas of neovolcanic activity in the Caucasus region. According to these data, the youngest volcanic events occurred in the terminal Pleistocene–Holocene, which makes this region potentially hazardous with respect to future volcanic activity
V. A. Lebedev
added a research item
Collision-related Quaternary mafic volcanism to the north of Lake Van (Eastern Anatolia, Turkey) occurred by eruptions from both volcanic centres and extensional fissures trending approximately north–south. We report new major, trace and rare earth element abundances, Sr–Nd–Pb isotope ratios and K–Ar ages for basaltic and more evolved hawaiitic and mugearitic lava flows. The new K–Ar ages indicate that magmatic activity occurred between 1.0 and 0.4 Ma. The volcanic products consist of mildly alkaline lavas, ranging in composition from basalt to hawaiite and mugearite. Energy-constrained assimilation and fractional crystallization (EC-AFC) model calculations suggest that the least evolved basaltic samples were unaffected by the combined effects of fractional crystallization and crustal contamination processes, in contrast to the more evolved hawaiitic and mugearitic lavas, which have experienced up to 2–3% crustal assimilation. Calculations based on crustal temperatures and Curie point depths indicate that the magma chamber, from which the basic to evolved lavas were derived, might be located at a depth of around 6–8 km, within the upper crust. Enrichment of large ion lithophile elements and light rare earth elements relative to high strength field elements, and higher 87Sr/86Sr and Pb isotopic ratios and lower 144Nd/143Nd of the least evolved basaltic samples indicate that the mantle source region of the Quaternary mafic magmas might have been enriched by melts that were derived from subducted sediments with a partial melting degree of around 10% rather than from Altered Oceanic Crust melts and fluids. Our model melting calculations show that the basaltic melts might have been produced by melting of a mantle source containing both amphibole and garnet with a partial melting degree of ~3%. Results of our petrological models indicate that a metasomatized mantle source, which was infiltrated by a mixture of 93% mantle melt and 7% sediment melt plus 0.01% residual rutile, added to mantle melt, could have been the source composition of the basaltic melts that produced the Quaternary mafic volcanism.
V. A. Lebedev
added 2 research items
3D version (with orography) of the Tendürek Volcano map. Compiled by V.A. Lebedev, 2016©. Appendix B to the paper Lebedev V.A. et al., 2016a //Petrology, 24(2), 127-152. Please, remember about copyrights and references!
The series of two papers presents a comprehensive isotope-geochronological and petrological- geochemical study of the Late Quaternary Tendürek Volcano (Eastern Turkey), one of the greatest volcanoes within the Caucasian–Eastern Anatolian segment of the Alpine foldbelt. The second article discusses the results of petrogenetic modeling, role of AFC-processes in the petrogenesis of magmas and the nature of mantle source of the Tendürek Volcano. Based on geochronological data, geochemical and isotope-geochemical (Sr-Nd-Pb) characteristics of the studied rocks we suggest the petrological model which well describe the evolution of magmatic system of the Tendürek Volcano during the whole period of its activity. The data obtained indicate that the igneous rocks of the Tendürek Volcano belong to the same homodromous volcanic series (trachybasalt–tephrite–phonotephrite–tephriphonolite–trachyandesite–trachyte–phonolite), which are dominated by the intermediate and moderately-acid varieties of the eruption products. The leading role in the petrogenesis of the lavas was played by the fractional crystallization processes, which, according to isotope-geochemical data, were sometimes complicated by the assimilation of upper crustal material. The mantle reservoir responsible for the magmatic activity within the major part of the Eastern Anatolia in the Late Quaternary time was represented by the OIB-type mantle. It was subject to slight metasomatic changes as a result of earlier deepening and remelting of the Arabian Plate slab, which was subducted under the region through the end of the Miocene. The depth of the magma-generating source is estimated at around 80 km, which corresponds to the upper part of the asthenospheric wedge under the region, based on geophysical data.
V. A. Lebedev
added a research item
The paper presents detailed isotope-geochronological, geological, and petrologic-mineralogical data on lavas of one of the greatest Quaternary magmatic area in the Greater Caucasus, the Kazbek neovolcanic center, including polygenetic Kazbek stratovolcano and a number of subordinate volcanic cones in its vicinities. The research was conducted based on a representative collection of more than 150 geological samples that characterize most of the volcanic cones and lava flows of different age, some of which were known previously, and other were discovered by the authors. The high-precision K-Ar data obtained on these materials make it possible to reproduce the evolutionary history of youngest magmatism at the Kazbek center and evaluate the total duration of this evolution at ~450 ka. The magmatic activity was subdivided into four phases (at 460-380, 310-200, 130-90, and <50 ka) with long-lasting interludes in between. Because the latest eruptions occurred in the Kazbek vicinity in the Holocene, this volcano is regarded as potentially active. The volcanic rocks of the Kazbek center make up a continuous compositional succession of basaltic (trachy)andesite-(trachy)andesite-dacite and mostly belong to the calc-alkaline series. The principal petrographic characteristics of the rocks and the composition of their phenocryst minerals are determined, mineral assemblages of these minerals are distinguished in the lavas of different type, and the temperature of the magmatic melts is evaluated. A principally important role in the petrogenesis of the Kazbek youngest magmas is proved to have been played by fractional crystallization and replenishment of mafic melts in the magmatic chambers beneath the volcano, which resulted in their mixing and mingling with the residual dacite melt and the origin of high-temperature hybrid andesite lavas. The comprehensive geological studies, involving interpretation of high-resolution satellite images, allowed the authors to compile the first detailed (1 : 25 000) volcanologic map of the Kazbek center and a geochronologic chart supplemented with a stratigraphic column, which illustrate the origin sequence of the volcanic vents and their lava flows, geological relations between them, as seen in reference geological sections, and variations in the composition of the magmatic products with time.
V. A. Lebedev
added a research item
An isotope-geochronological study of young magmatism in the central part of the Greater Caucasus (Kazbek neovolcanic area) on the territory of Russia and Georgia has been carried out. It was proved for the first time that, in the Early Pleistocene, there was a separate impulse of magmatic activity in this area. The K–Ar and Rb–Sr methods have been used to date the Early Pleistocene volcanism (1.45–1.35 million years ago, Calabrian) and to specify the regional geochronological scale of the Neogene–Quaternary magmatism. The area of endogenic activity for the period identified was contoured on the basis of the integrated isotope-geochronological, petrological-geochemical, and geological data. It has been shown that the Early Pleistocene volcanism inherits the area of Neogene volcanism in the Kazbek region and, therefore, presents the final impulse of the second (Pliocene) stage of the Late Cenozoic magmatism. Thus, Early Pleistocene volcanism was not a precursor of Late Quaternary magmatism as the latter has other spatial patterns of the location of volcanic centers.
V. A. Lebedev
added an update
Geological map of the Kazbek neovolcanic center (Greater Caucasus), 1/25000
Geological map of the Javakheti neovolcanic area (Lesser Caucasus), 1/200000, version of 2017
Geological map of the Samsari Range (Republic of Georgia), 1/50000
Geological map of the Çaldiran area (Eastern Turkey), 1/100000
Geological map of the Kars-Digor plateau, Eastern Turkey, 1/100000
Geological map of the Geghama highland, 1/100000
 
V. A. Lebedev
added an update
The Beginning of Volcanic Activity within Sredinny Metamorphic Massif (Sredinny Range, Kamchatka) - Published, August 2017, Doklady Earth Sciences
Quaternary tectonics of recent basins in northwestern Armenia - Published, October 2017, Geotectonics
Early Pleistocene volcanism in the central part of the Greater Caucasus - Published, November 2017, Doklady Earth Sciences
The chronology of magmatic activity and petrological-mineralogical characteristics of Quaternary lavas of the Kazbek Volcano (Greater Caucasus) - In press, Petrology, January 2018
Miocene-Pliocene volcanism in the Central Armenia: geochronology and the role of AFC-processes in the petrogenesis of magmas - In press
The age and matter sources for Au-sulfide mineralization in the Tanadon deposit (Greater Caucasus, Republic of North Ossetia-Alania) - In press
Petrology and Geochemistry of the Quaternary Mafic Volcanism in the northeast of Lake Van, Eastern Anatolian Collision Zone, Turkey - Accepted manuscript (November, 2, 2017), Journal of Petrology
Pliocene – Early Pleistocene history of the Euphrates valley applied to Late Cenozoic tectonics of northern Arabian Plate and its surrounding, Eastern Turkey - Under review
Quaternary geology and origin of the Shirak Basin, NW Armenia - Under review
 
V. A. Lebedev
added a project goal
Project: "The geochronology and peculiarities of evolution of young catastrophic volcanism in the Northern Eurasia: evidence from the isotope studies"
The study of chronology and periodicity of Neogene-Quaternary volcanism in the Northern Eurasia (the territory of Russia and adjacent countries), the obtaining of isotope-geochemical data for determination of petrogenesis of young volcanic rocks, the formulation of criterias for long-term forecast of the possibility for resumption of catastrophic volcanic eruptions in the future within the concrete regions.