Age of Ichinsky and Khangar Stratovolcanoes (Sredinny Range,Kamchatka)     

Pevzner  M. M.  Lebedev  V. A.  Volynets  A. O.  Tolstykh  M. L.  Kostitsin  Yu. A.  Babansky  A. D. 《Doklady Earth Sciences》2019,489(2):1413-1416

Doklady Earth Sciences - The K–Ar isotopic age of the beginning of formation of Ichinsky (0.35) and Khangar (0.4) stratovolcanoes is established for the first time, as well as the age of the...  相似文献   

Late Cenozoic volcanic activity in western Georgia: Evidence from new isotope geochronological data     

Lebedev  V. A.  Sakhno  V. G.  Yakushev  A. I. 《Doklady Earth Sciences》2009,427(1):819-825

The products of volcanic activity from the Kutaisi area and Guria (western Georgia) were studied in terms of isotope geochronology to determine the age of rocks and to confirm their attribution to Cenozoic formations. The results obtained show that the erupted rocks in the Kutaisi area were formed during the three pulses of Mesozoic volcanic activity: the Bajocian, Kimmeridgian-Tithonian, and Turonian-Santonian. It was shown that no displays of Late Cenozoic volcanism occurred in this region of the western Georgia. Because of this, its inclusion into the Central Georgian neovolcanic province, earlier supposed, seems to be improper. By the data of isotope geochronology, Guria is the only region of western Georgia where volcanic activity occurred in post-Paleogene period. Two pulses of young volcanism were revealed: of about 15.5 and 9–7.5 My. The former was related to the introduction of syenite intrusion, and the latter, to subaqueous exudation of subalkaline Neogene lavas. All the outcrops of Neogene rocks we found and dated in Guria fit within the well-pronounced sublatitudinal linear band which probably represents the occurrence in the Middle Miocene of a local zone of extension appearing under conditions of total compression during the collision of the Eurasian and Arabian lithospheric plates.

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Across‐axis variations in petrophysical properties of the North Porcupine Basin,offshore Ireland: New insights from long‐streamer traveltime tomography     

Manel Prada  Franois Lavou  Muhammad Mudasar Saqab  Brian M. O'Reilly  Sergei Lebedev  John J. Walsh  Conrad Childs 《Basin Research》2019,31(1):59-76

The Porcupine Basin is a Mesozoic failed rift located in the North Atlantic margin, SW of Ireland, in which a postrift phase of extensional faulting and reactivation of synrift faults occurred during the Mid–Late Eocene. Fault zones are known to act as either conduits or barriers for fluid flow and to contribute to overpressure. Yet, little is known about the distribution of fluids and their relation to the tectono‐stratigraphic architecture of the Porcupine Basin. One way to tackle this aspect is by assessing seismic (V_p) and petrophysical (e.g., porosity) properties of the basin stratigraphy. Here, we use for the first time in the Porcupine Basin 10‐km‐long‐streamer data to perform traveltime tomography of first arrivals and retrieve the 2D V_p structure of the postrift sequence along a ~130‐km‐long EW profile across the northern Porcupine Basin. A new V_p–density relationship is derived from the exploration wells tied to the seismic line to estimate density and bulk porosity of the Cenozoic postrift sequence from the tomographic result. The V_p model covers the shallowest 4 km of the basin and reveals a steeper vertical velocity gradient in the centre of the basin than in the flanks. This variation together with a relatively thick Neogene and Quaternary sediment accumulation in the centre of the basin suggests higher overburden pressure and compaction compared to the margins, implying fluid flow towards the edges of the basin driven by differential compaction. The V_p model also reveals two prominent subvertical low‐velocity bodies on the western margin of the basin. The tomographic model in combination with the time‐migrated seismic section shows that whereas the first anomaly spatially coincides with the western basin‐bounding fault, the second body occurs within the hangingwall of the fault, where no major faulting is observed. Porosity estimates suggest that this latter anomaly indicates pore overpressure of sandier Early–Mid Eocene units. Lithological well control together with fault displacement analysis suggests that the western basin‐bounding fault can act as a hydraulic barrier for fluids migrating from the centre of the basin towards its flanks, favouring fluid compartmentalization and overpressure of sandier units of its hangingwall.  相似文献   

Miocene–Pliocene Volcanism of Central Armenia: Geochronology and the Role of AFC Processes in Magma Petrogenesis     

V. A. Lebedev  I. V. Chernyshev  A. K. Sagatelyan  Yu. V. Goltsman  T. I. Oleinikova 《Journal of Volcanology and Seismology》2018,12(5):310-331

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The Structure,Composition, and Conditions of Generation for the Early Cretaceous Mongolia–East-Transbaikalia Volcanic Belt: The Durulgui–Torei Area (Southern Transbaikalia,Russia)     

F.?M.?StupakEmail author  E.?A.?Kudryashova  V.?A.?Lebedev  Yu.?V.?Gol’tsman 《Journal of Volcanology and Seismology》2018,12(1):34-46

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Water retention effects on elastic properties of Opalinus shale     

Alexey Yurikov  Maxim Lebedev  Marina Pervukhina  Boris Gurevich 《Geophysical Prospecting》2019,67(4):984-996

Shales play an important role in many engineering applications such as nuclear waste, CO₂ storage and oil or gas production. Shales are often utilized as an impermeable seal or an unconventional reservoir. For both situations, shales are often studied using seismic waves. Elastic properties of shales strongly depend on their hydration, which can lead to substantial structural changes. Thus, in order to explore shaly formations with seismic methods, it is necessary to understand the dependency of shale elastic properties on variations in hydration. In this work, we investigate structural changes in Opalinus shale at different hydration states using laboratory measurements and X-ray micro-computed tomography. We show that the shale swells with hydration and shrinks with drying with no visible damage. The pore space of the shale deforms, exhibiting a reduction in the total porosity with drying and an increase in the total porosity with hydration. We study the elastic properties of the shale at different hydration states using ultrasonic velocities measurements. The elastic moduli of the shale show substantial changes with variations in hydration, which cannot be explained with a single driving mechanism. We suggest that changes of the elastic moduli with variations in hydration are driven by multiple competing factors: (1) variations in total porosity, (2) substitution of pore-filling fluid, (3) change in stiffness of contacts between clay particles and (4) chemical hardening/softening of clay particles. We qualitatively and quantitatively analyse and discuss the influence of each of these factors on the elastic moduli. We conclude that depending on the microstructure and composition of a particular shale, some of the factors dominate over the others, resulting in different dependencies of the elastic moduli on hydration.  相似文献   

Elastic properties of sands,Part 1: Micro computed tomography image analysis of grain shapes and their relationship with microstructure     

Zubair Ahmed  Maxim Lebedev 《Geophysical Prospecting》2019,67(4):723-744

Elastic properties of an unconsolidated sand are largely dependent on the elastic properties of its constituent grain and the micro-structure that defines how the grains are arranged within themselves. Coordination number, that is the average number of contacts a grain has with its neighbours, and contact surface area are the two parameters closely related to the microstructure. Moreover, grain shapes and sorting also have substantial influence on these parameters. To calculate these parameters and find any potential relationships with the shape factors, we acquire high-resolution micro computed tomography images of four mechanically compacted unconsolidated dry sand samples that are of different shape factors and sorting indices. After a comprehensive voxel-based data processing, we calculate shape factors such as sphericity and roundness of each grain in all samples. Using own algorithm, we then calculate the coordination number and contact surface area. Results show that samples of well-sorted and higher spherical and rounded grains have higher coordination number and contact surface area than the samples of poorly sorted and lower spherical and rounded grains. Among the poorly sorted samples, coordination number is largely dependent on the fraction of larger grain sizes present in the sample. Inside any given sample, grains of lower sphericity tend to have higher coordination numbers. Moreover, more spherical and rounded grains have greater contact surface area with their neighbours.  相似文献   

Haüyne Alkaline Basaltoids Found in the Lesser Caucasus (Kapan District,Armenia) and Their Middle Pleistocene Age     

Lebedev  V. A.  Chernyshev  I. V. 《Doklady Earth Sciences》2020,492(2):426-430

Doklady Earth Sciences - The results of isotope–geochronological study of Quaternary mafic volcanism in the Kapan neovolcanic center (Southern Armenia) are discussed. The rocks studied are...  相似文献   

Solar-wind flow past a cometary ionosphere     

V. B. Baranov  M. G. Lebedev 《Astrophysics and Space Science》1988,147(1):69-90

An axisymmetric gasdynamical model of an interaction between the solar wind and comet atmospheres is formulated. Photoionization of the cometary neutral particles as well as their resonance charge-exchange are taken into account to determine the flow in the distured region containing three discontinuity surfaces (two shocks and the contact discontinuity).It is shown that these two processes are significant for many comets. The problem so formulated is solved numerically. A dependence of the obtained solutions on comets gas production, charge-exchange cross-section, photoionization time scale and other parameters is studied. The numerical solutions are in good agreement with the experimental data obtained during the spacecraft missions to the comet Halley in March 1986.  相似文献   

Structure of the region of solar wind—Interstellar medium interaction and its influence on H atoms penetrating the solar wind   总被引：1，自引：0，他引：1  

V. B. Baranov  M. G. Lebedev  M. S. Ruderman 《Astrophysics and Space Science》1979,66(2):441-451

The structure of the region of interaction between the solar wind and the interstellar medium in the two-shocks model (TSM), first suggested by Baranovet al. (1970), is numerically calculated.For this problem our model is true only for charged particles of the interstellar medium interacting with the solar wind, since the free paths of neutral particles are very long and any hydrodynamical approximation would be incorrect.The shapes of the outer and inner shocks, the shape of the contact surface and the distribution of the parameters inside the interaction region are calculated, and are universal and correct for other astrophysical applications such as interstellar bubbles (Weaveret al., 1977), the stellar wind flow around a globule (Dyson, 1975), the interaction of stellar winds in binaries (Prilutzky and Usov, 1976), and so on.The problem of the effect of the charge exchange of H atoms with interstellar gas protons decelerated by an outer shock on H atoms penetrating the solar system is considered using the calculated results (Wallis, 1975). This effect is shown to influence essentially the estimate of H-atom concentration in the interstellar medium based on theL -scattering data.  相似文献