Riftogenic Structures Research Articles

Prospects for exploration of hydrogen fields in riftogene structures of platforms (the case of the Dnieper-Donets Aulacogene)

This paper shows the prospect to find industrial-scale hydrogen accumulations in riftogenic structures of platforms using the example of the Dnieper-Donets Aulacogene, located in the southern part of the East European Platform. Within the Dnieper-Donets Depression, geological and geophysical methods indicate a significant number of deep faults and ring structures of volcanogenic and explosive origin promising increased hydrogen content. Possible locations of the most propitious areas of hydrogen concentration are associated with faults in rift systems and their nearest margins, as well as with explosive and volcanogenic ring structures with signs of modern activation. At a fine-grained level, the prospectivity of the area is determined not only by the specified structural relationship, but also by the set of geophysical characteristics (thermal, seismic, gravity, electrical conductivity, magnetic) and the corresponding geological and hydrogeological parameters. Areas for further more detailed investigations within the Sribne and other ring structures, Southern Near-Edge Fault, Northern Near-Edge Fault were identified based on the data on geological and geophysical materials, satellite images, and field work. We defined high-priority and low-priority territories. Areas for initial investigations using satellite images, gas sampling (hydrogen, helium, methane, etc.), primary geophysical surveys (with evaluation of intermediate reservoirs and cap rocks) were identified. The primary results can be used to plan pilot shallow drilling and wells sampling. The areas for priority deeper drilling and sampling are selected by the sum of results obtained and data comparison. The paper presents the results obtained 30 km east of Kyiv as an example of field assessment of H2 degassing in a local depression. The results show that hydrogen concentrations at depths of 0.45 to 1.5 m are near zero outside the local depression. The maximum values of H2 concentration (up to 3300 ppm 1.5 m deep) are characteristic of the point inside the depression.

Comparative tectonics of the White Sea paleorift system and other continental rifting systems

Research subject. The Riphean paleorift system of the White Sea, most of which is overlain by the waters of the White and Barents Seas and the platform cover of the East European Platform. This allowed numerous researchers to classify it as an aulacogen. The system was revealed by geophysical methods in the relief of the crystalline basement of the platform in the form of a frame of deep extended trenches of northwestern strike, subparallel to the edge of the East European platform.Materials and methods. Personal observations of the authors within the Onega-Kandalakcha paleorift, Baikal rift zone; a detailed study of seismostratigraphic sections of these zones; extensive literature data on the structure of modern rift zones. A comparative analysis of the structure of the most studied and currently active Baikal and East African rift systems, as well as the Karoo rift system of the Late Paleozoic origin with the paleorift system of the White Sea.Results. The following types of structural parageneses, which are characteristic of both modern rift systems and ancient paleorift systems, were identified. 1. Genetic relationship (inheritance?) of riftogenic structures with more ancient basement structures. 2. Structural paragenesis of concentric complexes in rift propagation zones. 3. Comparability of the area of horizontal extension of the lithosphere of the White Sea paleorift system with extension zones of modern continental rifts. 4. The fundamental similarity of the structure: the complex of paleorifts of the White Sea with modern continental rift systems: the presence of long deep trough segmentation of grabens and semi-grabens separated by bridges, which were accommodation zones with polarity reversal along the strike of the rift zone, displacement of the rift relative to the mantle ledge, the existence of a gently dipping normal fault (detachment), etc.Conclusion. The riftogenic nature of the aulacogens in the northeastern segment of the East European Platform has been confirmed.

Geology, physical-chemical and geodynamic conditions for the formation of Sokolovsk and Krasnokamensk granitoid massifs (South Ural)

The article describes the geological structure of the Sokolovsk and Krasnokamensk massifs located in the central part of the Western subzone of the Chelyabinsk-Adamovka zone of the Southern Urals. They are of Lower Carboniferous age and break through the volcanogenic-sedimentary deposits of the Krasnokamensk (D3kr) and Bulatovo (S1-D1bl) strata. It was found that these intrusions belong to the gabbro-syenite complex and are composed of gabbroids (phase I) and syenites, quartz monzonites, less often monzodiorites (phase II). The rocks of the second phase predominate (90–95%). Gabbros belong to the normal alkaline series of the sodium series and are close to tholeiitic mafic rocks, the formation of which is associated with riftogenic structures; syenites correspond to moderately alkaline series with K-Na type of alkalinity. It has been proved that in terms of their petrographic, petrochemical, geochemical, and metallogenic features (content of TiO2, K2O, Na2O, Rb, Sr, distribution of REE, the presence of skarn-magnetic mineralization), the rocks of the massifs under consideration undoubtedly belong to the gabbro-granite formation. Crystallization of the Sokolovsk and Krasnokamensk intrusions occurred at a temperature of 880–930 °С in the mesoabyssal zone at a depth of about 7–8 km (P = 2.2–2.4 kbar). At the postmagmatic stage, the transformation parameters of the initially igneous rocks were, respectively, T = 730–770 °C, P = 4.0–4.2 kbar. The fact that these massifs belong to the gabbro-granite formation makes it possible to include them, together with Bolshakovsk, Klyuchevsky, Kurtmaksky and Kambulatovo, into the Chelyabinsk-Adamovka segment of the South Ural Early Carboniferous rift system.

METALLOGENY DURING THE PRECAMBRIAN STAGE IN GEOLOGICAL EVOLUTION OF THE EARTH

The article explores the genesis of ore deposits and their global distribution in Precambrian tectonic structures of the Earth (metallogeny). Ore-bearing structures developed successively from the plume-tectonic Paleoarchean-Paleoproterozoic (3.6–2.2 Ga) anorogenic type in riftogenic structures to the mostly plate-tectonic synorogenic type in Paleo- Neoproterozoic (2.2–0.6 Ga) accretion and collision structures. Special attention is given to the difference in the genesis of deposits between the Northern and the Southern hemispheres due to geodynamic differences. The article is of interest for geologists specializing in ore deposits, and for geology students.

STRUCTURAL-KINEMATIC EVOLUTION OF THE EARTH'S CRUST OF THE DNIEPER-DONETS PALEORIFT<br/> Part 2. Systematic organization of post-rift structural transformations

At the stages of platform tectonic activation rock geomasses in riftogenic structures acquires the ability to horizontal displacement due to internal structural and material transformations under the influence of reid deformation in stress metamorphism zones. The article highlights the results of tectonophysical studies of post-rift complications of the architecture of the Dnieper-Donets paleorift. The structural manifestation of reid dynamic tectonics in the geological structure of the sedimentary complexes of the paleorift platform cover is strike-slip transformations of its primary linear elements — fault systems, tectonic segments, geoblocks, and anticlinal structure zones.Using the original method of reconstruction of tectonic stress and strain fields and tectonophysical analysis of geostructures, based on an analysis of anomalies of potential geophysical fields and vertical amplitudes of neotectonic movements, the territorial distribution, tectonic position and natural kinematic mechanisms of the formation of secondary deformation structures of tectonic flow, linear and areal concentration zones of reid deformations of subregional and zonal scales, size from hundreds of meters to tens of kilometers.The natural mechanisms of reid deformation are caused by horizontal-plane movements of structural elements, rocky ensembles of discontinuities and local structures of tectonic flow dynamically conjugated with them. The usual tectonic process of reid dynamic tectonics is the collision warping of the horizons of the sedimentary sequence, which causes deformation structure formation. Under its influence, structural waves of deformations of horizontal-plane tectonic flow were formed in the sedimentary cover of the paleorift, which determine the longitudinal tectonic segmentation of the geostructure and the main features of the system organization of the latest paleorift architecture.

Synrift Sandstones and Mudstones: Bulk Chemical Composition and Position in Some Discriminant Paleogeodynamic Diagrams

The bulk chemical composition of synrift sandstones and associated mudstones is analyzed. Distribution of their fields in the discriminant paleogeodynamic diagrams SiO2–K2O/Na2O (Roser and Korsch, 1986) and DF1–DF2 (Verma and Armstrong-Altrin, 2013) is examined. In terms of the bulk chemical composition, the sandstones correspond mainly to graywackes, litites, arkoses, and subarkoses. The samples also include sublitites and quartz arenites, as well as a significant part of psammites (with log(Na2O/K2O less than –1.0) that are lacking in Pettijohn’s classification diagram. This fact supports our conclusion based on the results of mineralogical-petrographic studies: the sedimentary infill of riftogenic structures combines immature sandstones, clastic framework of which is derived from local provenances represented by diverse igneous and sedimentary rocks. Synrift mudstones, relative to sandstones, are composed of a more mature clastic material. Distribution of data points of mudstones in diagram F1–F2 (Roser and Korsch, 1988) suggests that they were sourced mainly from sedimentary rocks. Contents of the majority of main rock-forming oxides in synrift sandstones are almost similar to those in silty–sandy rocks of the Upper Precambrian–Phanerozoic sedimentary megacomplex in the Russian Plate, but differ from contents in the average Proterozoic and Phanerozoic cratonic sandstones, as well as the average composition in the upper continental crust. It is shown that the distribution of synrift sandstones and mudstones in diagram SiO2–K2O/Na2O lacks any prominent features, and their data points cluster in the fields of terrigenous rocks of passive and active continental margins. In diagram DF1–DF2, fields of the studied psammites and mudstones occur in zones of the riftogenic and collisional settings. We believe that the boundary between these zones in the diagram occupies a different position, and this suggestion needs further examination.

Synrift clayey rocks: bulk chemical composition and position on discriminant paleogeodynamic diagrams

The paper analyzes the bulk chemical composition and distribution of the fields of syn-rift clayey rocks on a number of discriminant paleogeodynamic diagrams. It is shown that, in general, there are significant variations in the bulk chemical composition for syn-rift clayey rocks. Thus, for example, the average SiO2 content varies from 44.74 to 66.42 wt. %, the average content of Al2O3 varies from 16.62 to 29.92 wt. %, and the K2Oaver are in the range 0.24 ... 5.77 wt. %. Based on the distribution of the figurative points of the syn-rift clayey rocks of various objects/riftogenous structures in the F1–F2 diagram, it can be assumed that the sources of fine aluminosilicoclastic were magmatic and sedimentary rocks of a wide range of compositions. The substantial overlap of the fields of various objects in the classification diagrams [(Na2O + K2O)/Al2O3]–[(Fe2O3tot + MgO)/SiO2] and K/Al–Mg/Al indicates, in general, the similarity of the compositions of the syn-rift fine-grained clastic rocks of various types of riftogenic structures. The localization of the composition fields of the clayey rocks of different riftogenous structures on such discriminant paleogeodynamic diagrams as K2O/Na2O–SiO2/Al2O3 and SiO2–K2O/Na2O suggests that they do not allow correctly distinguishing between syn-rift clayey rocks and fine-grained rosks of other geodynamic environments. The position of the syn-rift clayey rocks fields presented in our database on the diagram DF1–DF2 has its own characteristics. In most cases, they occupy a particular position in the areas characterizing collision and rifting environments, and a number of fields are located in all three classification areas of this diagram. A significant part of the midpoints of the syn-rift clayey rocks is localized in the DF1–DF2 diagram in the collision field. It seems that all of the above indicates that the DF1–DF2 diagram also does not allow us to obtain a correct information about the geodynamic nature of terrigenous associations.

Syn-rift Clayey Rocks: Bulk Chemical Composition and Position on Discriminant Paleogeodynamic Diagrams

The paper analyzes the bulk chemical composition and distribution of the fields of syn-rift clayey rocks on a number of discriminant paleogeodynamic diagrams. It is shown that, in general, there are significant variations in the bulk chemical composition for syn-rift clayey rocks. Thus, for example, the average SiO 2 content varies from 44.74 to 66.42 wt. %, the average content of Al 2 O 3 varies from 16.62 to 29.92 wt. %, and the K 2 O aver are in the range 0.24 ... 5.77 wt. %. Based on the distribution of the figurative points of the syn-rift clayey rocks of various objects/riftogenous structures in the F1–F2 diagram, it can be assumed that the sources of fine aluminosilicoclastic were magmatic and sedimentary rocks of a wide range of compositions. The substantial overlap of the fields of various objects in the classification diagrams [(Na 2 O + K 2 O)/Al 2 O 3 ]–[(Fe 2 O 3tot + MgO)/SiO 2 ] and K/Al–Mg/Al indicates, in general, the similarity of the compositions of the syn-rift fine-grained clastic rocks of various types of riftogenic structures. The localization of the composition fields of the clayey rocks of different riftogenous structures on such discriminant paleogeodynamic diagrams as K 2 O/Na 2 O–SiO 2 /Al 2 O 3 and SiO 2 –K 2 O/Na 2 O suggests that they do not allow correctly distinguishing between syn-rift clayey rocks and fine-grained rosks of other geodynamic environments. The position of the syn-rift clayey rocks fields presented in our database on the diagram DF1–DF2 has its own characteristics. In most cases, they occupy a particular position in the areas characterizing collision and rifting environments, and a number of fields are located in all three classification areas of this diagram. A significant part of the midpoints of the syn-rift clayey rocks is localized in the DF1–DF2 diagram in the collision field. It seems that all of the above indicates that the DF1–DF2 diagram also does not allow us to obtain a correct information about the geodynamic nature of terrigenous associations.

Horizontal movements of geomass in continental riftogenic geostructures (on the example of the Dnieper-Donets paleorift). Part 3. Systemic organization of post-rift reid deformations

Formulation of the problem. The article covers the results of tectonophysical studies on the structural manifestations of the collisional evolutionary stage of the continental crust, which complicate the riftogenic architecture of Dnieper-Donets paleorift. At the stages of platform activation, rocks in riftogenic structures acquire volumetric tectonic mobility due to internal structural-material transformations and deformation under the influence of reid tectonics. The structural manifestation of reid tectonics in the geological structure of the basement and sedimentary complexes of the Dnieper-Donetsk paleorift cover is the horizontal movement of its primary riftogenic segment tectonic elements, lineaments, geoblocks, tectonic structures and secondary deformation structure formation. Review of previous publications and studies. The paleotectonic situation in the paleorift before the start of the rifting is covered by the results of plate-tectonic reconstructions carried out for Ukrainian Shield. Structural-kinematic evolution of the continental crust in the adjacent territories of the Shield in the south was reproduced, covering the stages of collision with subduction of the crust and spreading followed by the extension of continental microplates. On this basis, the important role of ancient even-petty folded structures of sub-meridional extension is determined in the structure of paleorift foundation. Methods. In geotectonic studies an original technique was used for reconstructing the fields of tectonic deformations and tectonophysical analysis of geostructures, based on potential geophysical fields anomalies and vertical amplitudes of neotectonic movements. Results. It was established that structural waves of secondary deformations of horizontal-plane tectonic flow were formed under the influence of mechanisms of reid tectonics. It is shown that they determine the longitudinal tectonic segmentation of the modern paleorift structure. The tectonic position and natural kinematic mechanisms in the formation of the tectonic flow local structures, linear concentration zones of reid deformation of subregional and zonal scales, ranging in size from hundreds of meters to tens of kilometers, were studied. Scientific novelty and practical significance. In the regular submeridional direction of compression axis regional field of tectonic stresses, longitudinal structural waves of the volumetric tectonic flow of geomass formed in the sedimentary cover of the paleorift under the influence of the processes of reid tectonics. The natural mechanisms of reid deformation are caused by horizontal-planar displacements of structural elements, rocky ensembles of discontinuities and local structures of reid deformation dynamically conjugated with them. A common tectonic process of reid dynamic tectonics is collision warping of the sedimentary sequence horizons, which determines the main features of the system organization of the latest paleorift architecture and its modern longitudinal tectonic segmentation.

СТРОЕНИЕ И УСЛОВИЯ ОБРАЗОВАНИЯ КРАЕВОГО ПЛАТО И ОСТРОВА CОКОТРА (ФИЗИЧЕСКОЕ МОДЕЛИРОВАНИЕ). ЧАСТЬ 1. СТРОЕНИЕ ОСТРОВА CОКОТРА

The structure of the eastern part of the Gulf of Aden is peculiar for the presence of a submerged plateau and the island of Socotra, which were formed at the initial stage of its formation. With the beginning of continental rifting in the Oligocene-Miocene, more ancient riftogenic structures of the Mesozoic age were reactivated. This was most revealed in the relief in the Guardafuy graben, which cuts off the base of the Socotra plateau from the shelf of the modern eastern tip of the Horn of Africa. During tension, there were significant rotational deformations of the entire plateau. Socotra Island is divided into two parts by the large Hadibo transfer zone. The morphostructure of the elevated eastern part is determined by the asymmetric arch-like Hajhir Mountains. The western part is deformed much more strongly than the eastern part and is strongly broken by steeply falling faults. The continental margins of Socotra Island in the eastern province of the Gulf of Aden are amagmatic, asymmetrical and fractured by a series of faults and detachments. The difference in their structure is explained by the peculiarity of the transition from continental rifting to spreading, associated with the hyper-extension of the continental crust. In order to understand the conditions of riftogenesis, under which the formation of the continental block of the submerged marginal plateau and the island of Socotra is possible, the authors carried out a physical simulation, the results of which are presented in Article 2.

Middle–Late Paleozoic Duplex Rifting of the Barents Continental Margin and the Role Played in Formation of the East Barents Megabasin

Based on analysis and interpretation of seismic and other geological-geophysical data, duplex rifting is identified in the Paleozoic evolution of the South Barents Basin. Its first, pre–Late Devonian, phase was manifested on the southeastern side zone that limited the Pechora Plate structures. After a certain pause, a second, pre–Late Carboniferous phase involved the western Barents Sea region, including the slope of the Central Barents Rise and the western South Barents Basin. Thus, Late Paleozoic riftogenic structures in the western and southeastern South Barents Basin formed at different times. All this caused an asymmetric structure profile and asynchronicity of evolution of the rift system sides. In the Mesozoic, under the effect of formation of the Novaya Zemlya fold-and-thrust structure, the asymmetry of the riftogenic trough became even more contrasting.

Bimodal intraplate magmatism of the Yenisei ridge as evidence of breakup of Rodinia and opening of the Paleoasian Ocean at the western margin of the Siberian Craton

The petrological–geochemical and isotopic–geochronological studies of contrasting rocks of the Yenisei Regional Tectonic Zone of the Yenisei Ridge allowed identification of the period of formation of riftogenic structures accompanied by intraplate magmatism. The extension processes are reflected in dike swarms of bimodal associations of anorogenic granites and intraplate mafic rocks with an intrusion age of 797–792 Ma. The formation of this belt is related to the Neoproterozoic extension along the western margin of the Siberian Craton, which occurred during breakup of the Rodinia Supercontinent and origination of the Paleoasian Ocean.

Late Mesozoic rifting at the flanks of the Dzhagda segment of the Mongolia-Okhotsk collisional orogen: global and regional aspects

The role of rifting in the formation of the recent structure of the Mongolia-Okhotsk orogen is extremely high, but it is still underestimated with regard to flanks of the Dzhagda segment of this orogen. Current researches refer to a combination of physical and chemical processes in the depth of the lithosphere, as well as interactions between the Izanagi, Eurasian and Pacific plates as explanations of repeated rifting events in East Asia. Upwelling of the asthenosphere due to significant differences in the lithosphere thickness (150–200 km under cratons, and only 100 km under orogenic belts) was viewed as a cause of rifting. It was assumed that rifting was controlled by mantle plumes, volcanism and heat regime. Structures bordering the Mongolia-Okhotsk orogen from north and south were considered as superimposed or marginal troughs. Recent studies have revealed numerous riftogenic Late Mesozoic structures in the Central Asian orogenic belt, which resulted from the collision of the Siberian and North Chinese cratons. New geological survey and geochemical data on volcanites confirmed the riftogenic origin of the Zeya-Uda (or Uda) and Nora-Selemdzha troughs bordering the Mongolia-Okhotsk orogen from north and south, respectively (Fig. 1, and 2). Geology and geophysics of those troughs has been described. It is noted that riftogenic volcanites formed later in the east than those in the west. The Late Mesozoic rifting is widely manifested in North Eastern Asia across the area exceeding two million square kilometers, from Lake Baikal to the Sikhote-Alin region (west to east) and from the Southern Yakutia basins to North China (north to south). It is evidenced by intra-continental rifts of various trends, volcanic provinces and extension structures along large strike-slip faults [ Ren et al., 2002 ]. The Uda and Nora-Selemdzha marginal troughs located along the Dzhagda segment of the Mongolia-Okhotsk orogen give evidence that compression was replaced by extension in the study area. Rifting structures may be due to physical and chemical processes, the development of plumes [ Yarmolyuk et al., 2000 ], as well as the interaction between the Pacific and Eurasian lithospheric plates. Volcanic activity took place earlier in the west and then propagated to the east due to the shifting of the subduction zone in this direction. This paper analyzes regional and global geological events on the basis of new drilling data and the geochronological dating of volcanites. It describes the Late Mesozoic stage of rifting at the flanks of the Dzhagda segment of the Mongolia-Okhotsk collisional orogen.

Tectonics and metallogeny of the junction zone between the North Asian craton and Pacific tectonic belt

The tectonics and metallogeny of the junction zone between the North Asian craton and Pacific tectonic belt are considered. This zone is characterized by a wide variety of structures superposed on the metamorphic basement, which was formed in the course of a multistage geologic development of the craton from the Precambrian to the Cenozoic. They are related to the craton evolution and its response to the collision and subduction processes in the adjacent orogenic belt, processes in the passive and active continental margins, and plume magmatism. The geological structure of the region includes blocks of metamorphic rocks of the Aldan–Stanovoi shield, Paleoproterozoic volcanogenic troughs, Mesoproterozoic–Neoproterozoic and Early Paleozoic structures of the platform cover, Late Paleozoic volcanic and terrigenous troughs, structures of the Late Mesozoic Okhotsk–Chukotka volcanic belt of the active continental margin, and Late Cretaceous riftogenic structures formed in response to plume magmatism. In total, six metallogenic epochs are recognized in the development of ore mineralization: Archean–Early Paleoproterozoic, Late Paleoproterozoic, Mesoproterozoic, Neoproterozoic, Late Paleozoic, and Late Mesozoic. The minerageny of the junction zone between the craton and Pacific belt is highly diversified, being characterized by distinct evolution in time and space. Each development stage features its own set of mineral resources.

The structure of the lithospheric mantle of the Siberain craton and seismodynamics of deformation waves in the Baikal seismic zone

The structure of the lithospheric mantle of the Siberain craton and seismodynamics of deformation waves in the Baikal seismic zone

Geologic structure of Western Primorye: Structuring dynamics

The first data are reported on the structuring dynamics of Western Primorye. The analysis of the structural parageneses of the least studied macro- and mesolevels of the arrangement of the geologic space allowed us to distinguish three sequentially superposed structural patterns (parageneses), each of which was formed by its own stress field during separate geodynamic periods: the Late Proterozoic-Early Paleozoic, the Middle-Late Paleozoic, and the Mesozoic-Cenozoic. During the first two episodes of geodynamic activation (Late Proterozoic-Early Paleozoic), the main compression axis was oriented longitudinally. The first episode was characterized by the formation of a thrust-fold structural pattern. The second episode resulted in the superposition of the meridional riftogenic structures and, respectively, in the pull-apart normal-fault segmentation of the crystalline basement into mainly longitudinal blocks, which partially coincide with the previously distinguished terranes. During the latitudinal compression and oblate deformation that predominanted during the Middle-Late Paleozoic geodynamic period, the down-thrown and uplifted blocks were transformed into depressions and arches, respectively. The depressions were filled with Paleozoic sediments, while the primary rocks in the arches experienced granitization with the formation of two granitic complexes that joined terranes. The granites are characterized by shadow and shear-type fold and pseudofolded forms. The Mesozoic-Cenozoic period governed by NNW compression is divided into the Triassic-Jurassic, Early Cretaceous, and Tertiary tectonic episodes. During the Triassic-Jurassic period, the ENE-trending narrow arches and depressions were formed by warping. The arches accumulated granitized rocks, while the depressions were compensated for by the Early-Late Triassic sedimentary-volcanogenic sediments. All these processes led to the formation of structural complexes that joined and overlapped older complexes of meridional blocks (terranes) across the strike. Two subsequent Mesozoic-Cenozoic episodes manifested themselves in the discrete formation of coal-bearing depressions due to the NNW compression and ENE extension of the warping products.

Evidence for the Mesozoic endogenous activity in the northeastern part of the Fennoscandian Shield

There are several stages of endogenous activity identified in the geological evolution of the northeast� ern part of Fennoscandia; the longest of them finished 1.8 Ga and then this part of the craton stabilized and had a pattern with the structural features close to the modern ones. The following long amagmatic period of more than 1.3 Ga finished in the Paleozoic by plume� lithospheric processes that formed the Kola alkaline province (0.40–0.36 Ga) and completed the develop� ment of riftogenic structures of the southeast White Sea region [7]. Later geological evidence that could signify the manifestation of endogenic activity in the period from 350 Ma until the present has not been found within northeastern part of the shield. Assessment of geodynamic environments existing at the Phanerozoic stage in the evolution of northeast Fennoscandia and reconstruction of motion trend for the Kola megablock in the Paleozoic are of great importance for determination of what the localization conditions of mantle melts produced the Kola alkaline province were. The paleomagnetic method can be involved in solution of this problem; however, the interval of 400–340 Ma BP is the most discussed in the Phanerozoic segment of the apparent polar wander path (APWP) for the East European Craton because of the nearly total absence of reliable paleomagnetic poles of the Devonian age. In order to obtain new data corresponding the modern criteria of reliability, we carried out reconnais� sance paleomagnetic studies of dolerite and alkaline lamprophyric dyke swarms, whose ages fall within the interval of 390–370 Ma according to the geochrono� logical datings (Rb–Sr, Sm–Nd,

Geological nvestigations in the Chukchi Sea and the adjacent areas of the Arctic Ocean during the RUSALCA-2009 expedition

The Joint Russian-American LongTerm Census of the Arctic Project (RUSALCA) started in Novem� ber of 2003 for the longterm monitoring of the Arctic environment. The studied region comprises poorly studied areas of the Chukchi Sea and the adjacent seg� ment of the Arctic Ocean near the Russia-United States boundary. This area is characterized by maximal rates of the environmental changes in the Arctic dur� ing the last decades, which is expressed, for example, in the enhanced ice melting (Fig. 1). Therefore, this project was aimed at the longterm monitoring of the Arctic environment and searching for the factors responsible for these changes. In this connection, of importance is the testing of different hypotheses explaining such significant environmental changes in the region under consideration. The main of these hypotheses are the increased water and heat exchange via the Bering Strait, the strengthened air heat transfer in the northern direction, and the upwelling of rela� tively warm intermediate Atlantic waters, which pene� trate into the eastern Arctic Ocean along the Eurasian continental slope. There is also an assumption con� cerning the activated geological processes in this region based on the development of a graben-rift sys� tem of nearmeridional and nearlatitudinal riftogenic structures in the Chukchi Sea (Fig. 1) formed in the Mesozoic and activated in the Late Cenozoic. This system is best studied in the socalled Chukchi Gra� ben, a neotectonic structure extending from eastern Chukotka in the south to at least the Herald Trench in the Chukchi Sea in the north (Fig. 1). Its onshore part studied in eastern Chukotka (the Kolyuchino- Mechigment zone) hosts Late Cenozoic volcanics and many hydrothermal vents with a discharging water temperature up to 97

Aeolian deposits of rift zones

The evolution of contemporary aeolian processes in continental rift zones is one of the poorly explored issues in Quaternary geology. Associated with rift zones is the formation of aeolian zircon-rutile-ilmenite sands which are rich in various mineral resources and, primarily, in titanium, zirconium, uranium, and in other rare-earth elements. Using the Baikal rift system as an example, the characteristics of the occurrence at the rift zones (hollows) of contemporaneous unfixed aeolian sands are examined. Analysis of the morphological elements of aeolian deposits, their substance composition and development patterns is based on long-term field work on the study of aeolian sands in the depressions of the Baikal rift system as well as on graphical representations of riftogenic structures on remotely sensed material and, primarily, on space-acquired images.

Sedimentary basins and prospects of oil and gas deposits on the shelf of the Eastern Arctic

Numerous riftogenic structures of different ages and orientations are widespread on the vast shelf of the Eastern Arctic region. A schematic tectonic map presents the main structural elements of the Upper Brooksian (Cretaceous-Cenozoic) unit, through which contours of the Ellesmerian (Late Devonian-Jurassic) structures, being the most enriched in hydrocarbon resources in the region under consideration, are seen. Three large sedimentation basins are identified in the upper unit: the Vil’kitskii-North Chukchi, the South Chukchi, and the East Chukchi basins separated by the Central Chukchi Rise, which was most active at the Ellesmerian stage. By analogy with the areas studied both on the shelf and on the continental slope, models of the formation and accumulation of hydrocarbons are presented for each of these three basins, thus, allowing one to outline the zones prospective for gas and oil accumulation.