S. Yu. Sokolov

Tectonic subdivision of the Chukchi and East Siberian Seas

A tentative tectonic subdivision for the Chukchi and East Siberian seas has been created based on the processing and analysis of new satellite altimetry and magnetic data and published materials that include information in electronic formats. The Chukchi Sea shelf is composed of correlatives of the Alaskan tectonic zones. The main Alaskan thrust does not stretch into Wrangel Island but is instead located in the region of the South Chukchi Sea Basin. Most part of the shelf is occupied by a zone of zero or slight deformation. The North Chukchi Sea Basin along with the Vilkitsky Trough and the region of maximum subsidence in the Colville Trough make a single entity, the Novosibirsk–Alaska Basin.

Tectonic Evolution of the Knipovich Ridge Based on the Anomalous Magnetic Field

Calculation of the downward continuation for the anomalous magnetic field at the Knipovich Ridge showed more complicate segmentation of the spreading oceanic basement than was earlier considered. The structural pattern of the field is evidence that the area consists of no less than four segments separated by transform fracture zones with the azimuth of oceanic crust accretion about 310° and the normal position relative to the rift segments with the azimuth of 40°. The modern location of the axis of the Knipovich Ridge straightens the complicate divergent boundary between the plates in the strike-slip conditions between the spreading centers of the Mohns and Gakkel ridges. The axis is a detachment zone intersecting the oceanic basement having formed from the Late Oligocene. A new magnetoactive layer composed of magmatic products has not yet been formed in this structure.

Tectonic elements of the Arctic region inferred from small-scale geophysical fields

Satellite altimetry data, Bouguer anomalies, anomalous magnetic field, bottom topography, and Love wave tomography for the deepwater part of the Arctic Ocean Basin and East Siberian Sea have made it possible to detect several new regional tectonic elements. The basin area, 700 km wide and 1800 km long, extending from the Laptev Sea to the Chukchi Borderland is a dextral strike-slip zone with structural elements typical of shearing. The destruction of the Eurasian margin surrounding the Amerasia Basin occurs within this zone. The opening of the Amerasia Basin is characterized by intense plume magmatism superimposed on normal slow spreading in several areas of the paleospreading axis. Magma was supplied through three conduits with minor offsets, the activity of which waned partly or completely by the end of basin formation. The main central conduit formed the structure of the Alpha Ridge. The dextral strike-slip system, which displaces the Gakkel Ridge and structural elements in the basement of the Makarov Basin, most likely extends to the northern termination of the Chukchi Borderland.

Role of the Asthenosphere in Transfer and Deformation of the Lithosphere: The Ethiopian-Afar Superplume and the Alpine-Himalayan Belt

Seismic tomographic data showing the mantle structure of the Ethiopian-Afar superplume and various segments of the Alpine-Himalayan Orogenic Belt and their relationships with the adjacent megastructures of the Earth are presented. These data and their correlation with the geological evidence lead to the conclusion that lateral flows of mantle material are crucial for the evolution of the Tethys and its closure in the Cenozoic with transformation into an orogenic belt. The lateral flow of hot upper mantle asthenospheric matter spreading from the stationary superplume extending in the meridional direction (in present-day coordinates) was responsible for the accretion of the fragments torn away from Gondwana to Eurasia and for the development of subduction at the northeastern flank of the Tethys. The characteristic upper mantle structure of cold slabs passing into nearly horizontal lenses with elevated seismic wave velocity in the lowermost upper mantle is currently retained in the Indonesian segment of the orogenic belt. In the northwestern segments of this belt, a hot asthenospheric flow reached its northern margin after closure of the Tethys and onset of collision, having reworked the former structure of the upper mantle and enriched it in aqueous fluids. The effect of this active asthenosphere on the lithosphere gave rise to intense Late Cenozoic deformation, magmatism, and eventually resulted in mountain building.

Statistical assessment of variations in the compositional and P-T parameters of the evolution of mid-oceanic ridge basalts and their regional distribution

The formal statistical analysis of variations in the basalt compositions for the whole global system of mid-oceanic ridges (approximately 19000 analyses of quenched glasses), including cluster analysis, discriminant analysis, and the analysis of histograms and component covariations, provide new data on the petrological parameters of the evolution of mantle magmatism and the spatial distribution of its products depending on geodynamic environments. The results thus obtained make it possible to assess all available information on magmatism in mid-oceanic ridges and to specify tasks for the further research. The information thus obtained is required for the development of the petrological basis for a model of magmatism of six major basalt groups (P-T parameters, productivity of volcanism, mantle upwelling, etc.).

Recent tectonics in the northern part of the Knipovich Ridge, Atlantic ocean

The walls of the Knipovich Ridge are complicated by normal and reverse faults revealed by a high-frequency profilograph. The map of their spatial distribution shows that the faults are grouped into domains a few tens of kilometers in size and are a result of superposition of several inequivalent geodynamic factors: the shear zone oriented parallel to the Hornsunn Fault and superposed on the typical dynamics of the midocean ridge with offsets along transform fracture zones and rifting along short segments of the Mid-Atlantic Ridge (MAR). According to the anomalous magnetic field, the Knipovich Ridge as a segment of the MAR has formed since the Oligocene including several segments with normal direction of spreading separated by a multitransform system of fracture zones. In the Quaternary, the boundary of plate interaction along the tension crack has been straightened to form the contemporary Knipovich Ridge, which crosses the previously existing magmatic spreading substrate and sedimentary cover at an angle of about 45° relative to the direction of accretion. The sedimentary cover along the walls of the Knipovich is Paleogene in age and has subsided into the rift valley to a depth of 500–1000 m along the normal faults.

Hydrothermal fields in the Mid-Atlantic Ridge: Setting and prospects for further discoveries

Analyzed is the setting of active and inactive hydrothermal fields and sulfide occurrences on the Mid-Atlantic Ridge between 65◦N and 65◦S. Multifaceted interpretation of data has enabled a prediction of how sulfide mineralization is distributed in the Atlantic Ocean.

Toward postplate tectonics

Half a century ago, principles of the theory of lithosphere plate tectonics, or plate tectonics, were first formulated. Since then, the theory has become substantially more complicated and tectonic processes and phenomena have been identified that are not described by the theory. This relates to certain types of vertical movements, primarily to the newest uplifts that led to the formation of modern mountain systems. Comparison of geological processes (both those described by the theory of plate tectonics and those unexplained thus far) with data of the seismic tomography of the mantle has made it possible to outline a new tectonic model, according to which the source of observable tectonic manifestations is lateral flows of upper mantle matter, propagating from superplumes—flows of matter and energy rising from the mantle’s bottom. These lateral flows not only move lithospheric plates but also determine structural–substantial transformations of the lithosphere and the upper underlithospheric mantle, which lead to vertical movements and mounting building.

Structure and composition of the sedimentary cover in the Knipovich Rift valley and Molloy Deep (Norwegian-Greenland basin)

The multidisciplinary approach is used to analyze the structure of the sedimentary cover in the northern Knipovich Rift valley, Molloy Fracture Zone and synonymous basin, Svyatogor and Hovgard rises, Gorynych Hills, Litvin and Pogrebitskii seamounts, and western slope of the Spitsbergen Archipelago studied in Cruise 24 of the R/V Akademik Nikolaj Strakhov. Materials of the bathymetric survey with multibeam echo sounder, as well as continuous seismic and vertical acoustic profiling, revealed two main (NNW- and NNE-trending) systems of fractures in the neotectonic structure of the region. It was established that a system of NNE-oriented fractures, linear zones of the dominant development of keyboard deformations included, is consistent with the strike of magnetic anomalies reconstructed for this region. Tectonic aspects of the Knipovich Rift and prospects of its further development are considered. Based on the wave field pattern of continuous seismic profiling (CSP) records, four seismocomplexes indicating contrasting sedimentation settings and intense tectonic processes at different formation stages of the northern Norwegian-Greenland Sea are conditionally defined in the sedimentary cover of the study region. It was established the Molloy Fracture Zone is responsible for a system of horizontal reflectors of acoustically transparent structureless light spots (“blankings”) in the upper well-stratified part of the sedimentary section, which are characteristic of areas with ascending pore fluids. The micropaleontological study (palynomorphs of higher plants, dinocysts, planktonic foraminifers, and diatoms) revealed the presence of Miocene assemblages in sediments. Benthic foraminifers include late Paleocene-middle Eocene assemblages. The composition of rock-forming components demonstrates a directed succession of mineral-terrigenous associations from the feldspar-quartz type to mesomictic quartz-graywacke type.

Gas hydrates in the sedimentary cover of passive oceanic margins: Possibilities of prediction based on satellite altimetry data in the Atlantic and Arctic

Analysis of factual data on acoustic indicators of fluid occurrences, negative gravity anomalies based on satellite altimetry, tectonic deformations, and findings of ultramafic rocks and serpentinites was carried out. Such data make up stable sublatitudinal groups across the Atlantic Ocean. The image obtained suggests the following cause-and-effect series of processes: (1) tectonic deformations; (2) serpentinization of ultramafic rocks and generation of methane; and (3) accumulation of gas hydrates in the sedimentary cover near the continental margin. The second process is accompanied by the formation of negative gravity anomalies; the third process, by the specific reflection of fluids in the acoustic wave field. These facts provide a basis for forecasting the presence of gas hydrates based on reductions of the satellite altimetry data and regional maps of the sedimentary cover in the Atlantic and Arctic.