Kandalaksha Graben Research Articles

Specifics of the Formation and Syngenetic Deformations of the Sharvaozero Kame (North Karelia)

A study of a section exposed in a quarry near ​​the village of Loukhi revealed a radial kame ridge composed of horizontally layered lacustrine sands with cross-bedded sand lenses and interlayers of siltstone with a 0.2- to 1.2-m-thick horizon of convolutions occurring as wide synclines, narrow anticlines, and pseudonodules. The lacustrine sediments overlain by sand and gravel sediments with paleosols down the slope of the ridge give way to moraine boulder sands overlying the heavily dislocated strata. The objective of this work is to analyze the conditions for the formation of the kame and the deformation structures in its section as possible indicators of paleoseismicity. To account for the structural features of the section, it is proposed that the ridge formed as a result of the projection of sediments of a flowing subglacial lake, which emerged in the body of the glacier during the deglaciation period, onto the moraine. A structural analysis of reverse faults in the dislocated sediments proved their gravitational nature, which is not evident from glaciotectonics, indicating the immobility of the ice mass during ridge formation. Convolutions are developed in layers of a narrow granulometric range (fine-grained sands and silts), which is significantly different from seismites in subaqueous sediments of highly seismic regions. Therefore, these structures are not associated with seismic liquefaction, although the section is 40 km from the southwestern side of the Kandalaksha graben, where Holocene 8.0-point paleoearthquakes with moderate magnitudes were revealed. Thus, the study did not confirm the occurrence of ​​paleoearthquakes with M ≥ 6–6.5 in the study area during the Late Ice Age.

Identification of the Seismogenic Structure in the Area of Chupa (North Karelia) and Parameterization of Paleoearthquakes in the Kandalaksha Graben Region

In the area of the village of Chupa, three isolated ranges of paleoseismic dislocations were revealed, marking a NW-trending linear seismogenic structure and a total length of more than 14 km . The dislocations are young tectonic ditches and fissures, mainly trending NW, mass displacements of blocks, including against the slope, disarrayed stones, and seismic landslides. Using the nature of the distribution of seismic dislocations for two areas, isoseismic maps were constructed, which made it possible to estimate the magnitudes of paleoseismic events using the macroseismic technique. They amounted to 3.7 and 2.9, respectively, with a focal depth of H ≤ 1 km under the assumption that each range corresponds to a local seismic source. The isolated character of the distribution of the identified ranges may be associated with another, more severe paleoearthquake, traces of which have been preserved mainly in elevated areas of the relief (above 80 m). In the Early Holocene, these sites were separate islands, since the formation conditions for dislocations were limited to subaquatic spaces. For this variant, M = 5.5 and H = 5 km were calculated; the age of the event is the Early Holocene. The results, taking into account data on the micrograben of the Great Salma Strait, indicate the periodic occurrence of coastal and mainland faults, subparallel to the axis of the Kandalaksha graben, as well as Holocene shallow-focus earthquakes of medium magnitude with an epicentral intensity up to I = VIII on the ESI-2007 scale. A catalog of postglacial paleoearthquakes of the Kandalaksha graben region has been compiled (5 events), which can be used to construct earthquake recurrence graphs. This will make it possible to substantially refine the seismic regime of this structure.

ПРИМЕРЫ ВЗАИМОДЕЙСТВИЯ ГЕОДИНАМИЧЕСКИХ СИСТЕМ В МОРФОСТРУКТУРЕ СЕВЕРА ВОСТОЧНО-ЕВРОПЕЙСКОЙ ПЛАТФОРМЫ

To determine the nature of the contribution of current tectonic processes to the formation of morphostructural ensembles is an important task. This can be done by comparing the morphostructure with the expected consequences of the impact of geodynamic systems. In the border area of the Baltic Shield and the Russian Plate, within the Circumbaltic zone of dislocations, there is a chain of recent graben depressions. The location of the depressions is determined by the tectonophysical patterns of dislocation sampling and favorable local structural conditions. Depression arose as areas of tension with the superpositional interaction of two subordinate horizontally oriented newest geodynamic systems – pressing the Baltic shield onto the Russian Plate and pushing the geological substrate at the point of their junction in the perpendicular direction. In the northern part of the White Sea Depression, the “visor” of the Karelian massif is approaching to the region of oncoming progressive stretching around the Kandalaksha graben. The superposition of these processes is clearly expressed in relief. Thus, the formation of morphostructures in the area is strongly influenced by the interaction of geodynamic systems.

Revisiting the Origin of Seismicity in Fennoscandia

A review of the literature suggests that the seismic process in Fennoscandia (the Baltic Shield) is affected by at least four mechanisms: (1) northwest-to-southeast movement of the lithospheric plate under the Norwegian and Barents seas by spreading of the Mid-Atlantic Ridge from Iceland to Spitsbergen; (2) postglacial isostatic uplift; (3) local recent neotectonic movements; and (4) gravitational bending deformations on continental contact with the sea shelf along the Norwegian coast due to strong erosion from the rising crystalline domain of the Baltic Shield. The current seismicity of Fennoscandia is relatively low. The strongest earthquake in this area over the last 1000 years was the earthquake of 1627 which had a magnitude of M ≈ 6.5 and occurred in the Kandalaksha graben in the White Sea. However, Fennoscandia, including the Kola Peninsula and eastern Karelia, has a reliable history of a significant number of Pleistocene and even Holocene paleoseismic dislocations, whose parameters allow them to be associated with strong earthquakes which occurred at that time with magnitudes of 7–8 and even higher. It is likely that these paleo-events occurred at the last stage of the glacial age (9000–10 000 years ago) during the intense postglacial isostatic uplift of the Fennoscandia domain. Their possible recurrence can be estimated as tens of thousands of years from the time interval between consecutive glaciations. One should therefore recognize that the nature of current seismicity of Fennoscandia is determined by tectonic stresses caused by both the global effect of the northwestern uplifting lithospheric plate under the Norwegian Sea (a constant source of tectonic stress accumulation) and local tectonic uplifts (the north coast of Norway) or lowerings (the Swedish coast of the Gulf of Bothnia), rather than by postglacial stresses. In addition, the increased seismicity of southwestern Norway and the adjacent North Sea shelf is most likely caused by the formation of crest-like structures under the action of tensile stresses revealed here.

Updated data on the current seismicity of the White Sea and the Karelian region during the period 2005–2016

This article is the result of previous studies to clarify the seismicity of the White sea, supplemented by similar studies on the continental part of the Republic of Karelia. The relocated catalog of earthquakes was created for the period from 2005 to 2016 for White Sea and the Karelian region. With the help of proven methods, the parameters of the epicenters of identified earthquakes were relocated and a map of current seismicity was obtained. The parameters of the epicenters were specified using BARENTS travel-time model, a single methodological approach (using Generalized beamforming) and all currently available source data and bulletins of Russian and foreign seismic stations. The obtained seismic catalog allowed us to identify the main patterns of the distribution of current seismicity in the White Sea region. Seismicity of the White sea and the Karelian region is characterized as low-magnitude (generally of low magnitude with ML<2.0). Most earthquakes in the White Sea are characterized by a focal depths up to 20 km. Analysis of catalog shows that the majority of earthquakes are concentrated in the north-western part of the defined area, in the continental part of Karelia and Kandalaksha graben. Some earthquakes were recorded in the eastern and central part of the White sea.

Postglacial tectonics and palaeoseisic dislocation in the “Kovda” area (Kandalaksha bay, eastern Fennoscandian shield)

«Вестник Санкт-Петербургского университета. Науки о Земле» — научно-теоретический рецензируемый журнал, обобщающий результаты исследований в области геологии, гидрогеологии и геохимии, петрологии и экологии, ландшафтного планирования и геоморфологии, экономической и социальной географии.

The crustal structure of Onega-Kandalaksha paleorift identified by complex analysis of the anomalous magnetic field of the White Sea

Geological and geophysical studies recently conducted in the White Sea and the adjacent territory have provided new data on the deep structure of this region. Our study aims to conduct complex analysis of the anomalous magnetic field and the geological and geophysical data on the Onega-Kandalaksha paleorift located in the White Sea basin and the adjacent southeastern land area, and to develop a model showing its deep structure. The basis for analysing the magnetic field is the anomalous magnetic field (AMF) map constructed by the authors using the magnetic survey data consolidated by the Marine Arctic Geological Expedition (MAGE) in 2003–2008 and supplemented by the survey data of the Institute of Oceanology RAS in 2001–2004. The parameters of the magnetically active layer are estimated by the independent complementary methods of quantitative interpretation developed by the Laboratory of Geophysical Fields, P.P. Shirshov Institute of Oceanology RAS. This article describes a model showing the structure and formation of the magnetically active layer of the White Sea paleorift. Our study shows that the magnetically active layer of the paleorift system has a complex structure reflecting all the main stages in the evolution of tectonic activity in the White Sea region, from the Middle and Late Riphean to the last glaciation of the Quaternary period. The model includes three structural layers, each corresponding to a certain stage. The bottom structural layer is the base of the magnetically active layer, which reflects the continental rifting stage in the evolution of the White Sea mobile belt in the Middle and Late Riphean. The middle structural layer reflects the Middle Paleozoic (Late Devonian) stage of rifting reactivation, which is characterized by alkaline-ultrabasic magmatism and represented by swarms of alkaline dykes and diatremes, including kimberlite pipes. The top structural layer reflecting a high-frequency component of the AMF is related to the highly magnetic sources of anomalies located in the upper part of this structural layer. The characteristics of the top structural layer suggest that it formed in the Late Pleistocene – Holocene and developed during the final stage the tectonic activation of this region. The deep crustal structure of the White Sea basin is specified in our model showing the magnetically active layer for the low-frequency component of the AMF. In the southeastern part of the basin, magmatism products of the basic (Riphean – Vendian) and alkaline-ultrabasic (Middle Paleozoic) composition are abundant in the crust and provide for a strong magnetic source of anomalies, the lower edges of which are traced at the depths to 30 km. This probably reflects the most active plume-lithospheric interaction. Wedging and uplifting of the magnetically active layer northwestward along the Onega-Kandalaksha rift is related to the White Sea (Belomorsky) deep fault. This fault is a long-lived conduit that channels magma from the central portion of the plume, as evidenced by the igneous bodies of the basic composition in the basement and central parts of the sedimentary wedge in the Kandalaksha graben. The complex analysis of the AMF in the White Sea region suggests the presence of morphologically different igneous bodies in the upper crust in the study region.

Problems of the time of foundation and the tectonic evolution of the Onega — Kandalaksha paleorift in the light of the data of isotopic geochronology

Kandalaksha graben, located in the water-area of the White sea, is a part of the Onega-Kandalaksha paleorift of the Riphean time of foundation. It is filled with the terrigenous formations of the Terskaya suites ranging from 3 to 8 km by depth, while the age of the rocks of the Terskaya suite is still controversial, and according to different sources, ranges from 1300 to 670 Ma. This means that the time of the formation of Kandalaksha Graben is not precisely defined. In 2016, on the Tersky Bank of the Kola Peninsula, a sample of sandstones of the suite was selected. The age of the rock of 1390±25 Ma, i.e. the boundary of the early and middle Riphean, was determined by the K-Ar isotope method.. This corresponds to the time of the beginning of the stretching of the lithosphere and continental rifting. Quartz-microcline metasomatites formed on sand-shale spit of Terskaya suite in the zone of amethyst deposit of Cape Korablik gave the age of 821±170 Ma, determined by Sm-Nd method, and fluorite of the same rocks gave the age of 690±71 Ma. The last value is close to the age of the basalts from the Onega depression, defined by the same method. These data correspond to the momentum of stretching of the passive Timan margin of the Baltic area at the end of the late Riphean.

Results of the tectonic stress study of the Northern Eurasia regions

The article presents the results obtained by field tectonophysical methods applied to study tectonic stresses of the Northern Eurasia regions, including young and ancient platforms (West European, Timan–Pechora, Turan, West Siberian, East European, and East Siberian) and orogenic frame structures (Caucasus, Northern Tien Shan, Mongolia-Okhotsk system of mesozoids, and Sakhalin Island). Tectonic stress reconstructions provided the basis for analysing the influence of spreading in the North Atlantics and the Arctic on the stress state of the platforms in Northern Europe. A spatial boundary of the influence goes approximately along the margins of the Fennoscandian shield and the Russian plate in the north. Further southwards, the boundary is submeridional and extends from the western wing of the Byelorussian anteclise almost to the Eastern Carpathians. The stress reconstructions for this boundary show the WNW and W-E-trending axes of compression. The boundary line does not coincide with the Teisser-Tornquist line that represents the boundary between the platforms with heterochronous basements. However, it correlates well with heat flow anomalies. The boundary area is confined to the Baltic coast [Sim, 2000. Along the boundary area, near the Baltic Sea, there is an area wherein faulting is mainly caused by extension [Sim, 2000. In this setting, helium permeability is the highest, as shown by the crust map of the European part of the USSR [Eremeev,1983. Extension in this area is probably related to formation of young grabens in the Baltic shield. Changes in the compression axis orientation may be due to the alternating activations of the grabens in the submeridionalBotnicGulf and the latitudinalGulf of Finland. Reconstructions for individual faults show contradictions in the directions of shear displacements: both right- and left-lateral displacements are possible on the same fault segments, and the axes of compression can have either latitudinal or meridional orientations. The focal mechanisms of the Osmussaar andKaliningrad earthquakes (meridional and latitudinal axes of compression, respectively) give evidence of specific current neotectonic stresses in this area. Another zone is distinguished at 52°N from the above-described area. It is mainly sublatitudinal and detected along the southern flank of the Byelorussian anteclise. Further to the east, its orientation changes to SSW, and it roughly follows the SW boundary of theVoronezh anteclise. Reconstructions for the Ukrainian Shield, located south of this zone, show mainly the unstable orientations of the axes of compression. For the platforms inNorthern Eurasia, the tectonophysical methods reconstructed neotectonic stresses in the structures formed under the influence of intraplatform tectonic stresses. These are the residual gravitational horizontal compression stresses released by long-term denudation and uplifting of the structures, including the Khibiny massif of the Baltic Shield, theOlenek and Munsky massifs of the East Siberian platform. These structures are composed of the ancient Archaean-Proterozoic rock complexes, which have been subjected to predominantly vertical displacements for a long time, from the Paleozoic to the modern stage. Special attention should be given to the tectonic stresses ofSakhalin located at the boundary between the Eurasian and North American lithospheric plates. At the edges of these two largest plates, there are the Amur and Okhotsk microplates separated by theCentral Sakhalin fault, as described in some publications. Neotectonic stress reconstructions forSakhalinIsland show sublatitudinal compression and submeridional extension in the common stress field of shearing. The tectonophysical studies show that the neotectonic stresses differ in large structures: horizontal compression and shearing are typical of the uplifts (Kola Peninsula, Tien Shan, Sakhalin), while horizontal extension and extension with shearing are characteristic of depressions (Kandalaksha graben, depressions of theTatarGulf and theSea ofOkhotsk). Our studies provide the data on spacious ‘white spots’ in the modern stress maps ofNorthern Eurasia. The stress reconstructions for practically all the studied structures show that shearing is the dominant geodynamic regime in the study region.

The newest stage of development of the White Sea depression

Analysis of materials on the geological structure and tectonics of the White Sea depression area suggests that this depression existed in the Middle Pleistocene and was connected with the World Ocean. It is still impossible to determine the exact time of its formation due to an insufficient knowledge of the depression loose cover. However it is most likely that the depression was formed in the Late Miocene and Early Pliocene, when after the regressive development of the continental margin the shelf subsidence began. Probably in the Holocene the divergent regime was replaced by the transform regime. This period saw the subsidence of the Kandalaksha graben to about 150 m and the formation of the Kolvitsa graben. The crystalline rocks surrounding Kandalaksha bay were involved in the subsidence which is reflected in the isobase curve of the glacioisostatic uplift of the area. The combined impact of the tectonic component and the glacioisostatic uplift led to a rise of tensions which discharge caused a high seismic activity of the Kandalaksha graben and its environs.

GEOMORPHIC MANIFESTATION OF HORIZONTAL SPLIT MORPHOSTRUCTURES IN NORTH KARELIA

Deep, long, and narrow depression of Lake Paanaiarvi represents the geomorphic anomaly for the North Karelia. The depression is situated at the intersection of two large neotectonic faults bounding the block of the earth crust. This block lies in the zone of influence of Kandalaksha graben. According to the position of Lake Paanaiarvi's depression the latter may be interpreted as the split that was formed dew to drifting apart of the boundaries of the extension zone around Kandalaksha graben.

New data on tectonics of Onega-Kandalaksha paleorift (The White Sea)

The Onega-Kandalaksha paleorift is a part of the White Sea rift system along the northeastern edge of the East-European platform and formed under conditions of horizontal extension of the edge of continental plate in the Middle‐Late Riphean [1]. The structure of the paleorift is divided into three main segments: the Kandalaksha graben in the water area of the White Sea, the Central and Onega troughs [2], and several smaller troughs (Fig. 1). The paleorift segments are semigrabens of alternative polarity separated by dykes representing crests of crystal foundation. On the northwestern edge of the Kandalaksha trough, there is Kolvitsky [3], another relatively small segment of the rift structure of about 80 km long. It is also separated from the major graben by the slanting intertrough dyke, which is a prominent underwater sill of the crystalline basement protruded as islands of the Sredniye Ludy archipelago above the water surface in some places. This segment is a shallow northwestern part (up to 70 m) of Kandalaksha Bay with many small islands composed of foundation rocks. The Onega-Kandalaksha paleorift was active in the Paleozoic, when alkaline magmatism was especially developed and at the end of the Cainozoe when the modern basin of the White Sea was formed. The formation of the White Sea basin was predetermined structurally and tectonically, since the trough of modern Kandalaksha Bay of the White Sea inherits and renews the Riphean graben, which is shown by active lowering of the Kandalaksha graben followed by renewal of most of the faults and the appearance of numerous seismic foci along them. Despite that the White Sea is the only fully interior sea in Russia; its geology has been studied weakly until recent complex geophysical research in the White Sea basin [4, 5]. The results of those and other recent works conducted in that area change the existing opinions about the earth crust structure of the region in question. If previously the depth of sinking of the crystalline basement in the Kandalaksha graben composed of Riphean terrigenous formations was supposed to reach 3‐3.5 km, according to the latest seismic research of the RF CDP in the water area of the White Sea, this depth is up to 8 km. Thus, the thickness of Riphean deposits is increased actually by a factor of 2‐2.5; however, the area of their spreading was not exactly established. For example, the contemporary geological maps [6] show Riphean deposits in Kandalaksha Bay on the islands of the Sredniye Ludy archipelago and towards the northwest of them in the young (Late Cainozoe) Kolvitskii graben, which contradicts the reality.