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  • 1
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    Deep mechanisms in the Kyrgyz Tien Shan orogen (from results of seismic tomography) (2013)
    Siberian Branch of the Russian Academy of Sciences
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    Publication Date: 2013-07-01
    Description: Seismic-tomography studies were conducted in the Kyrgyz Tien Shan using two different observation schemes. The first was based on the arrival times of P and S waves from regional earthquakes recorded with local seismological networks (local scheme). Nonlinear tomographic inversion based on the LOTOS algorithm was used to construct the 3D distributions of P and S wave velocities in the crust beneath the Kyrgyz Tien Shan and to refine the earthquake locations. The second scheme was used to study the upper-mantle structure based on data from global earthquake catalogs (regional scheme). All the data on waves which at least partly travel within the volume studied were used here, including (1) those from regional earthquakes recorded at world seismic stations and (2) teleseisms recorded at the local stations. This approach was earlier applied to calculate the upper-mantle structure beneath Asia. We used a fragment of this structure beneath the Tien Shan and adjacent areas. A series of synthetic tests was performed to estimate the resolution provided by both schemes. The tomography shows traces of the delamination of the Tarim mantle lithosphere from south to north. Also, the local and regional schemes reveal evidence for cold-matter descent from north to south in the northern Tien Shan but on a much smaller scale. Low velocities in the upper mantle beneath the Tien Shan might indicate lithospheric thinning. These data suggest that mantle-lithosphere delamination is taking place underneath both the northern and the southern margins of the Tien Shan collision belt. Lack of the mantle lithosphere beneath the Tien Shan leads to lithospheric weakening and active deformation, thus causing intense orogeny. © 2013.
    Print ISSN: 1068-7971
    Electronic ISSN: 1878-030X
    Topics: Geosciences , Physics
    Published by Siberian Branch of the Russian Academy of Sciences on behalf of Novosibirsk State University.
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  • 2
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    Plate reconstructions in the Arctic region based on joint analysis of gravity, magnetic, and seismic anomalies (2013)
    Siberian Branch of the Russian Academy of Sciences
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    Publication Date: 2013-08-01
    Description: Based on the analysis of various geophysical data, namely, free-air gravity anomalies, magnetic anomalies, upper mantle seismic tomography images, and topography/bathymetry maps, we single out the major structural elements in the Circum Arctic and present the reconstruction of their locations during the past 200 million years. The configuration of the magnetic field patterns allows revealing an isometric block, which covers the Alpha-Mendeleev Ridges and surrounding areas. This block of presumably continental origin is the remnant part of the Arctida Plate, which was the major tectonic element in the Arctic region in Mesozoic time. We believe that the subduction along the Anyui suture in the time period from 200 to 120 Ma caused rotation of the Arctida Plate, which, in turn, led to the simultaneous closure of the South Anyui Ocean and opening of the Canadian Basin. The rotation of this plate is responsible for extension processes in West Siberia and the northward displacement of Novaya Zemlya relative to the Urals-Taimyr orogenic belt. The cratonic-type North American, Greenland, and European Plates were united before 130 Ma. At the later stages, first Greenland was detached from North America, which resulted in the Baffin Sea, and then Greenland was separated from the European Plate, which led to the opening of the northern segment of the Atlantic Ocean. The Cenozoic stage of opening of the Eurasian Basin and North Atlantic Ocean is unambiguously reconstructed based on linear magnetic anomalies. The counter-clockwise rotation of North America by an angle of ~. 15° with respect to Eurasia and the right lateral displacement to 200-250 km ensure an almost perfect fit of the contours of the deep water basin in the North Atlantic and Arctic Oceans. © 2013 .
    Print ISSN: 1068-7971
    Electronic ISSN: 1878-030X
    Topics: Geosciences , Physics
    Published by Siberian Branch of the Russian Academy of Sciences on behalf of Novosibirsk State University.
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  • 3
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    An integrate model of subduction: Contributions from geology, experimental petrology, and seismic tomography (2015)
    Siberian Branch of the Russian Academy of Sciences
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    Publication Date: 2015-01-01
    Description: We summarize the available knowledge of subduction gained from geology, petrology, and seismology and consider the advantages and drawbacks of each method. Regional and local seismic tomography reveals complex systems of fluid and melt migration at different depths above subducting slabs. The physicochemical evolution of the magma storage system maintaining active volcanism is modeled with reference to a wealth of geological and geophysical data. Subduction-related processes are discussed by examples of active (Kamchatka and Japan arcs) and ancient (Kokchetav metamorphic complex) subduction zones. Comprehensive geological and geophysical studies in Kamchatka and Japan prove valid the leading role of andesite magma in subduction of oceanic crust and, on the other hand, show that modeling independent migration paths of melts and fluids is problematic. The case study of Kamchatka provides more insights into melting in intermediate magma reservoirs at the depths about 50-80 and 30. km and highlights the significance of shallow magma sources at the pre-eruption stage. The Kokchetav metamorphics, which are exhumed suprasubduction rocks, offer an exceptional opportunity to estimate directly the compositions and ages of subduction-related melts. © 2015.
    Print ISSN: 1068-7971
    Electronic ISSN: 1878-030X
    Topics: Geosciences , Physics
    Published by Siberian Branch of the Russian Academy of Sciences on behalf of Novosibirsk State University.
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  • 4
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    Geodynamics and stress-strain patterns in different tectonic settings (2013)
    Siberian Branch of the Russian Academy of Sciences
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    Publication Date: 2013-04-01
    Description: Deformation patterns in subduction zones, feeder systems of volcanoes, and rifts are compared and investigated in terms of relations among elastoplastic strain, rheology, pore fluids, and temperature. Regional-scale subduction processes have been explored in segments of the Kuriles-Kamchatka, Izu-Bonin, and Mariana zones. Slab geometry constraints from the 3D velocity structure are used to model the balance of forces in the three subduction zones and to distinguish the regions of predominant push or pull. Stress and strain variations in suprasubduction crust are considered for the case of magma sources beneath the Klyuchevskoy group of volcanoes. Time-lapse (4D) seismic tomography shows crustal magma reservoirs to appear and disappear rapidly as the volcanoes become active or dormant, respectively. This behavior is due to rapid strain changes which cause fast flow of fluids and the ensuing decrease or increase of melting temperature in the magma reservoirs. In addition to subduction zones, stress-strain patterns are modeled for collisional (compressive) settings, with the example of the Altai-Sayan area and the Caucasus, and for the conditions of rifting (extension), in the case of the Vilyui basin. As the modeling shows, formation of a superdeep basin does not necessarily require the crust to stretch twice or more: only 20% stretching in the necking region is enough to produce a 10-15 km deep basin. © 2013.
    Print ISSN: 1068-7971
    Electronic ISSN: 1878-030X
    Topics: Geosciences , Physics
    Published by Siberian Branch of the Russian Academy of Sciences on behalf of Novosibirsk State University.
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  • 5
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    Concerning tectonics and the tectonic evolution of the Arctic (2013)
    Siberian Branch of the Russian Academy of Sciences
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    Publication Date: 2013-08-01
    Description: The particularities of the current tectonic structure of the Russian part of the Arctic region are discussed with the division into the Barents-Kara and Laptev-Chukchi continental margins. We demonstrate new geological data for the key structures of the Arctic, which are analyzed with consideration of new geophysical data (gravitational and magnetic), including first seismic tomography models for the Arctic. Special attention is given to the New Siberian Islands block, which includes the De Long Islands, where field work took place in 2011. Based on the analysis of the tectonic structure of key units, of new geological and geophysical information and our paleomagnetic data for these units, we considered a series of paleogeodynamic reconstructions for the arctic structures from Late Precambrian to Late Paleozoic. This paper develops the ideas of L.P. Zonenshain and L.M. Natapov on the Precambrian Arctida paleocontinent. We consider its evolution during the Late Precambrian and the entire Paleozoic and conclude that the blocks that parted in the Late Precambrian (Svalbard, Kara, New Siberian, etc.) formed a Late Paleozoic subcontinent, Arctida II, which again "sutured" the continental masses of Laurentia, Siberia, and Baltica, this time, within Pangea. © 2013 .
    Print ISSN: 1068-7971
    Electronic ISSN: 1878-030X
    Topics: Geosciences , Physics
    Published by Siberian Branch of the Russian Academy of Sciences on behalf of Novosibirsk State University.
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  • 6
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    Structure of the upper mantle in the Circum-Arctic region from regional seismic tomography (2012)
    Siberian Branch of the Russian Academy of Sciences
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    Publication Date: 2012-10-01
    Description: We present a new three-dimensional model of P-velocity anomalies in the upper mantle beneath the Circum-Arctic region based on tomographic inversion of global data from the catalogues of the International Seismological Center (ISC, 2007). We used travel times of seismic waves from events located in the study area which were recorded by the worldwide network, as well as data from remote events registered by stations in the study region. The obtained mantle seismic anomalies clearly correlate with the main lithosphere structures in the Circum-Arctic region. High-velocity anomalies down to 250-300 km depth correspond to Precambrian thick lithosphere plates, such as the East European Platform with the adjacent shelf areas, Siberian Plate, Canadian Shield, and Greenland. It should be noted that lithosphere beneath the central part of Greenland appears to be strongly thinned, which can be explained by the effect of the Iceland plume which passed under Greenland 50-60 million years ago. Beneath Chukotka, Yakutia, and Alaska we observe low-velocity anomalies which represent weak and relatively thin actively deformed lithosphere. Some of these low-velocity areas coincide with manifestations of Cenozoic volcanism. A high-velocity anomaly at 500-700 km depth beneath Chukotka may be a relic of the subduction zone which occurred here about 100 million years ago. In the oceanic areas, the tomography results are strongly inhomogeneous. Beneath the North Atlantic, we observe very strong low-velocity anomalies which indicate an important role of the Iceland plume and active rifting in the opening of the oceanic basin. On the contrary, beneath the central part of the Arctic Ocean, no significant anomalies are observed, which implies a passive character of rifting. © 2012.
    Print ISSN: 1068-7971
    Electronic ISSN: 1878-030X
    Topics: Geosciences , Physics
    Published by Siberian Branch of the Russian Academy of Sciences on behalf of Novosibirsk State University.
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