The East European Platform constitutes the Precambrian foundation of Europe and determines its main structural and geomorphological features.
The platform lies between folded structures of different ages. In the northwest, it is bordered by the Caledonides - folded mountain formations of the Atlantic mobile zone. In the east, it borders on the Hercynian folded structures of the Ural mobile zone. Hercynian folds frame the platform in the west. Alpine folded formations of the Mediterranean mobile zone adjoin the East European Platform from the south.
For the greater part of its borders, the East European Platform has sharp, secondary outlines. It is articulated with the Caledonides pushed over the platform by a tectonic suture. At all other contacts, the crystalline foundation of the platform is cut off by faults. Its margins are strongly submerged towards the foredeeps separating the platform from the adjacent mountain structures.
The modern tectonic relief of the East European Platform is determined by the system of Precambrian, Paleozoic, and Cenozoic faults of different ages discussed above. Faults divide the crystalline foundation of the platform into blocks, which determine its hypsometry.
An important role in the tectoorogeny of the platform cover of the East European Plain is played by subtectonic landforms - salt structures and brown coal domes, common in many provinces of the country.
Of great tecto-orogenic importance for the East European Platform are also nested subgeosinclinal folded structures, the only structures of their kind - the Donetsk and Timan ridges.
In the structure of the basement of the East European Platform, there are: the Ukrainian crystalline shield and the Volyn-Podolsk syneclise, or plate, the Baltic shield, the Voronezh anteclise, the Masurian-Belarusian anteclise, the Dnieper-Donetsk depression and the Donetsk ridge, the Black Sea and Caspian depressions, the Baltic syneclise, the Latvian saddle , Orsha-Kresttsovsky trough, Moscow syneclise, Pachelmsky trough, Sursko-Mokshinsky swell, Volga-Ural anteclise, Zhiguli arch, Caspian flexure, Omutinsky trough, Cis-Ural depression system - Abdulinsky trough, Osinskaya depression, Omutinsky trough, Pre-Timan trough and Timan ridge, Pechora syneclise. All these elements of the hypsometry of the crystalline basement are identified on the 1964 tectonic map of Europe. To some extent, they are associated with the distribution of geological formations and elements of the modern geomorphological surface.
These regional structures are characterized: some - shields - as areas of relief of a granite basement, others - uplands - as areas with a predominantly reflected relief, and still others - lowlands - as areas with a typical accumulative relief. The second and third categories of structural-geomorphological regions have a thick platform cover. This indicates the predominance of downward movements in the tectonic development of the East European Platform, starting from the Early Paleozoic. They identified the main feature of the tectonic relief, mostly low-lying plain, which distinguishes it from other continental platforms in the Eastern Hemisphere.
Within the East European platform, the Ukrainian and Baltic crystalline shields are distinguished, located respectively in the south- and north-western parts of the platform.
Ukrainian crystal shield adjacent to the Crimean-Carpathian mobile zone, the location of which reflects its outer edge.
The shield stretches from the northwest to the southeast of the river valley. Goryn to the Sea of \u200b\u200bAzov is almost 1000 km. Its width in some places exceeds 250 km. The distribution of the crystalline basement generally corresponds to the right-bank Dnieper and Azov uplands.
The surface of the crystalline rocks of the shield rises: in the north - the Ovruch ridge - up to 315 m, in the middle part - on the Bug region - up to 320 m and in the south - the Azov Upland - up to 327 m above sea level.
Towards the adjacent depressions, the surface of the shield first decreases gradually, then it is abruptly cut off by faults. In the lowered parts, the blocks of the crystalline basement are submerged to a depth of 3-5 km, and in the axial part of the Dnieper-Donetsk depression, more than 8 km. The marginal parts of the shield are in the form of plates inclined towards the depressions. Morphologically, they resemble shelves and in many cases were. For the most part, coastal marine deposits lie on the surface of its margins, as can be seen on the western, Podolsk, slope of the Ukrainian crystalline shield.
The steep buried slopes of the crystalline Precambrian basement are dissected by deep canyons and valleys, similar to those found on the continental slopes of the ocean floor. Like the latter, the valleys on the slopes of the Ukrainian crystalline shield and other shields have a complex, not yet fully elucidated origin. In this case, tectonics and river erosion played a decisive role in the formation of buried valleys. River valleys were laid down and developed in zones of tectonic disturbances, primarily faults. Marine abrasion, which was repeatedly renewed during the history of the geological development of the shield, when its steep slopes formed sea shores, had a certain significance in the development of the forms of buried valleys.
The age of the denudation surface of the Ukrainian crystalline shield is very ancient and varies in different parts of it. The remains of the most ancient platform cover on the shield are represented by the Ovruch formation. Its terrigenous-volcanogenic sequence is filled by a tectonic trough of an older Precambrian basement. At the end of the Precambrian, a similar cover, apparently, was already widespread on the East European Platform. Based on the occurrence of the Ovruch formation, it can be concluded that by the end of the Precambrian, the Ukrainian crystalline shield, as a large part of the East European Platform, as a whole had an already leveled surface. The beginning of the denudation alignment dates back to the late Archean - by the time when the desert crystalline plateau of the platform began to acquire a block structure due to the formation of faults in the Krivoy Rog system.
Between the completion of the formation of the Ovruch Series and the next stage of peneplanation of the shield, the southwestern part of the platform experienced significant uplifts, giving it the appearance of an elevated blocky country. Since the Riphean, especially in the early Paleozoic, there have been sharp deformations of the crystalline basement of the platform. Their consequence was the formation of deep faults, which outlined the main features of the modern tectoorogeny of the platform. The most important structural elements of the Early Paleozoic emplacement on the East European Platform are considered to be faults that limit the Baltic Shield, the Timan Upland, the Pachelma Trough, the Dnieper-Donets Depression, the western slopes of the Ukrainian Crystalline Shield, and its entire southwestern and southern edges. These also include the establishment of the Mediterranean and Ural mobile zones adjacent to the platform within their present boundaries, the Black Sea and Caspian depressions, as well as the Moscow region syneclise.
On the western slopes of the Ukrainian crystalline shield and the entire area of the Volyn-Podolsk syneclise plate that stood out at that time, shelf marine deposits were deposited in the Proterozoic and Early Paleozoic and later. The elephant, slightly inclined to the outer edge of the platform, maintains this position for many geological periods. The faults that bound the shield from the west and east were areas of volcanism. The basalts formed at that time take part in the structure of the local relief. Areas of basalt cover, buried at a considerable depth, were also found in the Dnieper-Donetsk depression.
Throughout the entire Paleozoic, Mesozoic and Paleogene, the Ukrainian crystalline shield experienced noticeable block movements that occurred in the foyer of a general subsidence or uplift. The raised blocks represent islands. Sediments were deposited on the lowered blocks in depressions on the shield surface. The available evidence indicates that already in the Cambrian time, the movement of shield blocks was differentiated. Remains of the Cambrian platform cover were preserved in the depressions of the shield surface in the Bug region, and the Carboniferous one - in the Boltysh depression.
Since the epoch of Jurassic and Cretaceous transgressions, the Ukrainian crystalline shield, apparently, periodically subsided below sea level. The deposits of that time are preserved in depressions and ancient buried valleys on the basement surface. At the beginning of the Paleogene, the territory of the shield throughout its entire length was a highly moistened land covered with abundant vegetation. A powerful brown-coal formation accumulated in its vast low areas. Marine sediments deposited in relief depressions contributed to the general leveling of the surface. During the Neogene period, the territory of the Ukrainian crystalline shield was covered by the sea only partially. The coastline has consistently shifted, approaching the modern one. At the border of the Neogene and the Quaternary, after the Kuyalnik Age, fluctuations in the position of the coastline occurred within modern level sea or slightly exceeded it.
In the structure of the relief of the shield, the marine environment left bright traces in the form of a stepped accumulative relief. These are flat surfaces spread over a large area, limited by weakly pronounced ledges within the location of ancient coastlines. They are most clearly preserved in the Sarmatian, Pontic, Cimmerian and Kuyalnik basins, the Baltic delta plain, as well as the ancient Euxinian, Karangatian and Azov-Black Sea marine terraces, known within the Black Sea lowland.
The last stage in the formation of superimposed elements of the relief of the shield belongs to the Quaternary period. Following the decrease in the level of the Kuyalnitsky basin, the development of modern river systems was completed. In the Pleistocene, in connection with the advance of the ice sheet on the territory of the shield, a number of abrasion and accumulative surface forms were formed, grouped depending on the position of the glaciation edge. A particularly significant place is occupied by landforms associated with moraine, fluvioglacial deposits and loess. Post-glacial geomorphogenesis was expressed in the formation of river terraces, valley-ravine landscapes, and eolian local forms.
The modern geomorphological appearance of the shield was created over a very long time. It includes elements of different ages, in varying degrees reworked and modified by both ancient and modern geological factors. The main features of the relief of the shield create: 1) forms of denudation of the crystalline basement; 2) structural plains; 3) water-genetic and glacigenic superimposed forms of the surface.
The structural-denudation relief of the Ukrainian crystalline shield, in addition to the previously noted factors, depends on the composition of the rocks, their occurrence and structural relationships, subsequently disturbed by faults and smoothed by denudation.
There are many extremely contradictory ideas about the structural features of the shield and the stratigraphy of the constituent sedimentary-metamorphic and igneous complexes. Most of the generalizing materials do not contain the necessary historical-structural and petrogenetic data and are still insufficient for tecto-orogenic conclusions.
On the denudation section of the shield, structural and geomorphological elements are exposed, to a certain extent reflecting the sequence of its formation. The most ancient formations of the shield are spilite-keratophyric sequences developed in the Orekhovo-Pavlograd region of the lower Dnieper region. Their age is 3000-3500 million years (Tugarinov, Voitkevich, 1966). The structure of the magnetic anomalies expressed in this area includes ultrabasites, metabasites, siliceous rocks with interlayers of mica schists, ferruginous quartzites interbedded with shales and gneisses. The iron ore concentrations associated with these deposits are located in islands within the zones of anomalies. The most characteristic among them are the areas of Tokmak-Mogila, Kamennaya Mogila and Pervomaisky in the basin of Kamyshevata, Salt, etc.
Mafic and related sedimentary-metamorphic rocks, in our opinion, are the original formations of the continental crust, island land centers, similar to modern islands of oceanic island arcs. The location of the siliceous-iron formation in the central and southeastern parts The shield also corresponds to the regularities of the location of the tectonic systems of islands on the earth's crust of the oceanic type.
In the modern relief, siliceous-iron-ore strata, due to their stability, create uplands - large hills, usually rounded. A prime example such a relief can serve as Tokmak-Tomb in the Sea of \u200b\u200bAzov.
Later formations are rows of sedimentary-metamorphic strata, concentrating around the oldest effusive-sedimentary formations. In conditions high degree metamorphism personality traits sedimentary strata are leveled and in modern building shield are represented mainly by gneisses and migmatites. Shales and crystalline limestones are of subordinate importance. The regularities of relationships between crystalline strata are obscured by the subsequent fragmentation of fields by faults into blocks, outpourings of mafic lavas, and denudation cut of blocks at different stratigraphic levels.
The most important structural and geomorphological feature of the Ukrainian crystalline shield are numerous plutons. A certain pattern is observed in their location, which consists in the concentration of intrusions depending on the general structural conditions. Three types of pluton tectoorogeny are distinguished. The first category includes relatively small intrusions of granitoids associated with ancient areas of formation of the continental crust. This type of intrusives prevails in the southeastern part of the shield, in the lower Dnieper and Azov regions. The spaces between the ancient areas are occupied by fields of gneisses and migmatites. The latter have a folded, plananticlinal and plaxiclinal structure. G. I. Kalyaev (1965) singled out a number of flat anticlines under the name of domes. The main ones are: Saksagansky, Demurinsky, Krinichansky, Kamyshevakhsky, Pyatikhatsky swell and Zaporozhye anticline uplift. In the structural field of gneisses and migmatites, including plutons, lies the Krivoy Rog zone, bounded by deep faults. Faults are associated with local submeridional folding. The folds are sometimes complicated by conformable intrusions of granitoids. This is the second type of shield plutons.
Intrusions of the second type, associated with folding, are always of considerable size and heterogeneous composition. They are most pronounced in the central part of the shield in the middle Bug region, the Teterev and Sluch basins. The boundary between the southeastern and central, as well as between the central and northern Volyn blocks of the Ukrainian crystalline shield is characterized by fault tectonics. These faults are associated with powerful discordant plutons of the third type - Korostensky, Novomirgorodsky and a number of other smaller formations. These are the latest plutonostructures within the shield.
Many intrusions of the shield take part in the structure modern relief. As can be seen from the example of the granites of the river. Kamenka, Stone Graves in the Sea of \u200b\u200bAzov, Korostyshev granites, etc., they make up rocky hills crowned with rocky hills - graves with characteristic forms of weathering. The ranges of rocky uplands generally correspond to the shape and size of the plutons.
The Volyn crystalline block is located in the northern part of the shield, in the basin of the Teterev, Sluch, Ubort and Uzha rivers and is limited by faults. The southern tectonic boundary runs schematically in the direction of Kyiv - Zhytomyr - Chudnov - Slavuta, which approximately coincides with the northern boundary of the distribution of migmatites of the Kirovograd complex. The given boundary is also the boundary of the forest (Polesskaya) and forest-steppe, as well as the northern boundary of the distribution of loess. This testifies to the tectonic, stable activity of the noted structural boundary for a very long period.
The surface of the crystalline basement of the Volyn block has an uneven sedimentary cover. In places of structural and denudation depressions, mainly confined to the fields of distribution of gneisses and migmatites, there is a sedimentary cover with an accumulative relief. The Krasnoarmeyskaya (Pulinskaya) depression, the Korostyshevsky lignite basin, etc., have such a surface. Throughout the rest of the block, the platform cover is characterized by an insignificant thickness, which only smooths out the sharpness of the outlines of crystalline rocks.
Positive landforms are created by outcrops of the crystalline basement. The features of the elevations are determined by the composition of the rocks that make them up and the method of preparation, depending on the denudation factor. These regularities are maintained throughout the territory of the Ukrainian crystalline shield and all shields in general.
In the basin of the Southern Bug, Ingulets, on the Azov crystalline massif and, apparently, in other places where the crystalline basement is cut off by denudation at the level of magma formation centers, dome tectonics of crystalline rocks, first noted by V. A. Ryabenko (1963), is exposed. Domes in the relief are rounded hills with smoothed protrusions, rising several meters or tens of meters above the surrounding area. These morphostructures are especially clearly expressed in the Berdichev region.
Canyons are one of the most common landforms of the Ukrainian crystalline shield. They are located in most cases in fault zones. These are inherited terrain elements. Significant in size and numerous canyons are known in the valleys of Teterev, Sluch, Uzh, Kamenka, etc. The most grandiose canyon in granite is located in the Dnieper valley between Dnepropetrovsk and Zaporozhye.
Weathering forms are exceptionally diverse on the Ukrainian crystalline shield. Within the distribution of granite massifs, heaps of weathering units, limited by tectonic cracks, predominate. Often they take on bizarre outlines. In the area of distribution of the Dnieper glaciation, the surface of crystalline rocks everywhere has traces of ice impact. In the Korosten-Shchors region, outcrops of red Korosten granite look like smoothed arenas, dotted with glacial scratches and scars, mostly elongated from north-north-west to south-south-east. In the watershed areas, granite outcrops have the shape of sheep's foreheads. Their steep ledges rise to 2-3 m. Forms of glacial denudation to the west of Korosten in the vicinity of the Barashi-Yablonets region are especially indicative. Over a fairly large area, continuous outcrops of gray granites and gneisses have the shape of typical curly rocks.
To the south-west of Korosten, granitoid outcrops smoothed by the glacier form separate rounded hills, occasionally scattered among the sandy plain. The rocks of labradorite are characterized by layered segregations (blocks) with slightly smoothed corners. Charnockite outcrops have peculiar forms of weathering. They accumulate in the form of fragments of variable shape and size. Alkaline igneous rocks form, during weathering, rounded blocks that occur among loose weathering products.
Peculiar geomorphological ensembles formed within the areas of ancient volcanism. They occupy the most significant areas in the junction zone of the Azov crystalline massif and the Donetsk Ridge, as well as in the fault zone that delimits the shield and the Volyn-Podolsk plate. On the northern outskirts of the Azov massif, in the basin of the Wet Volnovakha and the part of the Kalmius valley adjacent to its mouth, volcanic rocks form ridges along the valleys and rocks on the banks of the rivers. In a number of places, ancient lavas have preserved flow structures. In the basalt rocks located on the shores, a well-pronounced prismatic separation is sometimes observed. In the Goryn basin, on the western slopes of the shield, basaltic dikes appear as small hills against the background of the smoothed surface of the Polessky Plain.
The distribution area of the Krivoy Rog iron ore formation lies within the steppe accumulative plain. Against the background of the plain, in the sloping parts, the rocks of this formation form rocks, distinguished by a dark color and a metallic sheen. Notable among them is the Eagle Rock in Krivoy Rog - one of the few surviving relief monuments of this type. In the area of deposits of the Krivoy Rog series, landscapes are distinguished by the coloration of iron oxides. This is reflected in geographical names(for example, Zhovtiye Vody, Zheltorechensk).
In the geomorphology of the Ukrainian crystalline shield, the Ovruch Ridge occupies a special place. Sedimentary-volcanogenic rocks, mainly pyrophyllite schists and quartzites, take part in its structure. Along the bedding planes of quartzites, wind-cut signs are often found, indicating the continental origin of these rocks. The Ovruch series fills depressions in the surface of the crystalline basement and has a slightly noticeable synclinal occurrence. This is a structure of the plaksincline type, trough, characteristic of the platform cover.
The Ovruch Ridge exceeds the adjacent spaces by more than 100 m and is limited by steep slopes. The most elevated part of the ridge is devoid of a cover of post-Cambrian deposits. The lowered areas and slope parts of the ridge are covered with Quaternary deposits, represented by lacustrine, often ribbon loams and loess rocks 20-30 m thick. Numerous steep-walled ravines, cutting through the entire loess stratum, play an important role in the geomorphology of the Ovruch ridge. Huge alluvial fans are located at the mouths of ravines. In some places, they merge with their edges and form a proluvial terrace bordering its uplift. Near the southwestern slope of the ridge in the Norin floodplain, placers of Paleogene sandstone are distributed over a small area. Huge blocks of it create original features of the landscape, found everywhere where the Paleogene is exposed. Blocks of sandstone usually have a smooth surface and are covered with a dark crust. In addition to the environs of Ovruch, Paleogene sandstones take part in the structure of the relief in the vicinity of the area with. Squirrel - Mount Tochilnitsa, Barashi - Mount Lisuha, etc.
The destruction products of the crystalline basement were the source of material for the formation of sedimentary rocks and associated mineral concentrations. Significant masses of weathering products during geological time, undergoing repeated processing, were removed from it at a great distance, and only an insignificant part of them was fixed within the shield. In particular, practically valuable mineral concentrations are concentrated in depressions of the surface of the crystalline basement - tectonic depressions, modern and buried valleys, as well as on the slopes of the shield and in the zones of shallow deposits of epicontinental seas that have repeatedly advanced on its territory.
Baltic shield. In the northwest of the East European Platform, the crystalline basement is exposed over a large area of the Baltic Sea basin from the northern coast of the Kola Peninsula to Bornholm Island, in the Baltic Sea - in the south.
Throughout the Baltic Shield has tectonic boundaries. In the north, from the Varangerfjord to the White Sea, the shield is cut by a deep fault that delimits the Precambrian basement and the Caledonian structures. Relics of Precambrian structures have been preserved in the form of Rybachy and Kildin Islands. Outlines of the Kola Peninsula of fault origin. NW-trending faults extend southeast from the shield into the East European Platform. The origin and development of the Kandalaksha, Onega, and Mezen bays and the Varanger Fjord are obviously connected with sublatitudinal faults. The bath of the Baltic Sea is also a tectonic depression. Its origin is similar to the origin of the Orsha-Kresttsovskiy trough of the basement of the East European Platform, with which the basin of the Baltic Sea, according to the lead, is a syntectonic formation.
The southwestern boundary of the Baltic Shield is also of fault-tectonic origin. In this part, the shield limits a fault that cuts off the outer edge of the platform. It runs from southeast to northwest in the direction of Torun-Koszalin, on the coast of the Baltic Sea, south of about. Bornholm, Ystad, in the south of Scandinavia, Helspnger, on about. Zealand, and through the peninsula of Jutland, at the latitude of the city of Holstebro. The Øresund, Kattegat, and Oslo Straits are located in grabens at the site of submerged blocks of the marginal part of the East European Platform.
In the west, the Baltic Shield borders the Caledonides of the Scandinavian Mountains. The tectonic seam in the form of a flat arc runs from the northeast to the southwest from the upper reaches of the Varangerfjord to Laiswalm and Halgar, in the northern part of the Oslo graben. From the latter, the Precambrian boundary of the Baltic Shield continues in a sprat direction to the west, southwest, in the direction of Buki Fjord. Throughout the western boundary, the masses of Caledonides are pushed to the east, overlapping the crystalline basement of the shield. The thrust front is strongly dissected by denudation and protrudes sharply in the relief, and is of great structural and geomorphological significance.
The crystalline basement of the East European Platform within the Baltic Shield is elevated to a considerable height and in many areas has a mountainous relief. A certain regularity is observed in the distribution of the heights of its surface. The foundation is most elevated in the northwestern part and along the tectonic suture with the Caledonides. The surface marks of the crystalline basement reach 1139 m on the Finnmarken plateau, on the northwestern coast of Lake. Sturaele-Tresk 2125 m, south of the river valley. Jungen 580 m, Dalfjell mountains 945 m, Gausta, Southern Norway, 1889 m. The surface of the crystalline basement decreases towards the Baltic Sea.
In the southern part of Finland, the surface of crystalline rocks rises to 105 m - South Salpauselkä, to 235 m - east of Vaza. The eastern part of the Baltic Shield has a relatively lower surface compared to the western one. The fluctuation of heights here ranges from 0, on the coast of the White Sea, to 1189 m in the Khibiny mountains.
The orographic elements of the eastern part of the Baltic Shield have a consistent northwest strike. In this direction stretch the heights of the Kola Peninsula Keiva and the "tundra" Panskiye Lujarvik and others, the Kandalaksha and Onega bays of the White Sea, the Windy Belt ridge, the strip of lakes - Onega, Segozero, Vygozero, Kuito, Topozero, the elevations - West Karelian and Manselka. Most of the valleys of the innumerable lakes of the shield have a northwestern extent.
The orography of the crystalline basement of the Baltic Shield reflects, to a certain extent, the structure and composition of the rocks that take part in its structure.
The first reports on the structure of the Baltic Shield are given in the works of O. I. Mushketov and A. D. Arkhangelsky. Modern views about its structure are covered in the works of X. Väyuryunen (1954), K. O. Kratz (1963), A. A. Polkanov and E. K. Gerling (1961), as well as in explanatory notes to international tectonic maps Europe and Eurasia (Tectonics of Europe, 1964; Tectonics of Eurasia, 1966).
The structural field of the Baltic Shield is characterized by the distribution of sedimentary-metamorphic rocks of different ages. The oldest of them are gneisses and gneiss granites, the relict massifs of which have been preserved among later structural formations. The age of these rocks is 2500-3500 million years. Later formations of 1900-2000 and 2000-2500 Ma are represented by biotite, sillimanite-staurolite, amphibole gneisses and amphibolites with magnetite quartzites. These ancient formations of the shield are associated with igneous rocks - peridotites, gabbro-labradorites, gabbro-diabases and granites.
Other types of sedimentary-metamorphic rocks on the Baltic Shield include phyllites, micaceous, green, graphite, clayey, shungite and other shales, tuff schists, amphibolites and amphibole schists, quartzites, conglomerates, limestones and dolomites. Strongly deformed sedimentary-metamorphic strata are dominated by igneous rocks of diverse composition and age. The most developed among them are granites, syenites and quartz syenites, diorites, gabbro, peridotites, nepheline rocks, diabases, diabase tuffs, etc.
The Precambrian of the Baltic Shield is subdivided into a number of stratigraphic sequences bounded by sharp unconformity surfaces.
On the Baltic Shield, according to X. Väyrynen (1959, p. 53), within Finland, the exposed geological bodies “…are typical deep rocks that cooled at a depth of many kilometers (up to 10-15 km). Thus, we can get some idea of the extent of erosion and the amount of material that was moved from this area of the Earth as a result of slow destruction and transport by flowing water before the earth's surface reached the present level.
The overlying strata were demolished not only over the granites, but also over the shale belts, which meander between the granite areas in the form of seams, and also sometimes compose larger areas. They are primary surface formations, but they have been intruded everywhere by larger or smaller granite and other intrusive masses, which are the same deep rocks as within large massifs. Shales were transformed into mixed gneisses under the influence of intruded granites. This indicates the insular formation of the continental crust of the Baltic Shield.
There are six phases in the development of the main Precambrian structural zone in Finland. According to H. Väyrynen, where granites were intruded into the most ancient, early Archean shales, tectonics manifests itself in the form of plastic deformations. The axial planes of the folds are vertical or steeply inclined, the folds are isoclinal. Granite intrusions are not secant, injection gneisses have not formed here either, granite veins are rare; they are layered, with sharp contacts, often folded together with shales. Proceeding from this, X. Väyrynen wrote (1959, p. 273) that "the earth's crust, on which the shale strata were originally deposited, completely melted under them." The thickness of the sediments of the earth's crust had a thickness of only a few hundred meters. Later, when a thicker crust was formed, the folding was concentrated in separate folded belts flowing around the rigid areas and granite areas located between the folding belts.
The structure of the crystalline basement is reflected in the relief. In the area of Lake Ladoga, the structures are “younger than the latest folding of these shales, often open or filled with loose material cracks and fissure belts, which are clearly distinguished in the relief” (Väyuryunen, 1959, p. 280).
The structure of the eastern part of the Baltic Shield within Karelia is multi-storey. According to K. O. Kratz (1963), the floors are distinguished:
1) granite-gneiss basement composed of deeply metamorphosed Archean formations; against their background, early and late Proterozoic folded formations protrude;
2) metamorphosed and highly deformed geosynclinal deposits intruded by basic and acidic intrusions; lower Proterozoic;
3) a layer of gently folded weakly metamorphosed subgeosynclinal deposits; Middle Proterozoic;
4) platform, non-metamorphosed Upper Proterozoic and Paleozoic deposits.
The Karelians are considered as part of the Proterozoic folded region. Its folded structures are cut off by denudation and are preserved only in synclinal structural zones. The relatively well-studied Ladoga synclinorium is included among the latter. “It is distinguished by the development of thick, highly dislocated strata of the Sortavala and Ladoga series, cut through by intrusions of ultrabasic, basic and granitoid rocks. The folded structures of the synclinorium are complicated by blocks protruding on the modern surface, composed of the oldest granite-gneiss complex and massifs of post-Ladoga granitoids.
In the Ladoga synclinorium, there are more than a dozen blocks composed of ancient granite gneisses with relics of various gneisses and amphibolites, ranging in size from small to larger, 120-150 km 2 . …these granite-gneiss massifs appear as rigid cores of dome-shaped anticlines in the structure of folded shale strata overlying them” (Kratts, 1963, pp. 98, 102). The uplifts are welded together by relatively narrow synclinal zones of complexly folded deeply metamorphosed geosynclinal deposits and deep intrusions of the Lower Proterozoic. This is a typical ancient island structure (Bondarchuk, 1969, 1970).
In the highly dislocated Precambrian sequence of the Baltic Shield, two independent structural complexes are distinguished, corresponding to the main epochs of folding - the Belomorian and Karelian. The older Saami and later Sveko-Finnish formations, significantly reworked, are of subordinate importance in places during folding. The age of the Saami folded complex is considered to be at least 2200 million years. It is composed of sedimentary-metamorphic rocks of the geosynclinal type. These deposits can be traced in the structure of the Belomorian and granulite massifs.
The Belomorian structural stage, or Belomorids, is composed of a series of Archean amphibolites, gneisses, and granite-gneisses with a total thickness of 6000-8000 m. These rocks are crumpled into folds extending in a northwesterly direction. Belomorids have been preserved between massifs of later folding in areas adjacent to White Sea, and in southern Sweden.
The Belomorids of the Belomorian region have a very complex structure. Here stands out (Tectonics of Europe, 1964) the Central, Ensko-Lukhsky, synclinorium. It separates the Kandalaksha and Primorsky anticlinoria in the northeast and the Keriysko-Kovdovorzsky one in the southwest. The main folds are complicated by dome-shaped anticlines and transverse synclines extending in a northeasterly direction. In the northern part of the Belomorian massif, the folds are overturned mainly to the northeast, and in the southern part, to the northwest. The folded structures of gneisses, characteristic of higher sections of the Belomorids, are replaced with depth plastic deformations currents.
A characteristic feature of the structure of Belomorides are numerous and diverse igneous formations. In the structure of Belomorides, the Belomorian and granulite massifs are especially distinguished. Karelians adjoin them from the northeast and southwest, the articulation with which passes along faults. Intrusions of basic and acid composition are concentrated in the contact zone. Various intrusions are known in the fault zones of the Vetrenoy Belt, in northern Karelia. Faults also separate the Belomorian massif from the granulite massif in the western part. The latter is pushed over the Karelians of Lapland to the south and southwest.
Karelians- Proterozoic folded formations of the Baltic Shield. Their structure has been most thoroughly studied in Karelia (Kratts, 1963) and Finland (Väyuryunen, 1954). In the western part of the shield, apparently, Svecofennids and Gotids syntectonic with Karelids.
Rock complexes of the Archean and Proterozoic age take part in the structure of Karelids. Archean deposits form the foundation of the Karelids and are exposed over a large area of them. They are represented by gneisses, granite gneisses, migmatites, and amphibolites.
Proterozoic formations of Karelids are divided into three subgroups: lower, middle and upper. The most common are the Lower Proterozoic strata, represented by highly metamorphosed deposits. They are collected in vast synclinal zones, elongated in a northwesterly direction. The synclinal zones separate the anticlinal uplifts, on which there are almost no deposits of the Lower Proterozoic. Anticlinal uplifts are composed of Archean formations complicated by later igneous intrusions, predominantly of granite.
The Middle Proterozoic is composed of sedimentary, weakly metamorphosed strata of conglomerates, sandstones, quartzites, carbonate-shale-diabase formations, and shale-volcanogenic rocks. These sequences are collected in gentle folds, often inheriting the strike of the previous Proterozoic folding.
Upper Proterozoic deposits are common in the southern part of the Karelian ASSR. They are represented by strata of quartzites and sandstones and fill gentle synclinal troughs. Late Proterozoic igneous formations are widely developed, which are dominated by rapakivi granites, dolerites and gabbro-alkaline rocks in the northern part of the republic.
Let's characterize common features tectonic structure of the Karelids according to K. O. Kratz (1963). Horst-anticlinal uplifts composed of Archean formations predominate in the modern cut across the area. Narrow folded synclinal zones extend between these uplifts, composed of geosynclinal strata compressed into folds.
The main structural elements of the Karelids (from east to west) are: the Karelian synclinal zone, which is complexly articulated with the Belomorian massif, the Central Karelian massif, the East Finland synclinal zone, adjacent to the Lapland massif in the north, including the Ladoga syncline in the south; in the southwest, the East Finland synclinal zone articulates with the Central Finland and Vyborg massifs; the synclinal zone of the North Norland Karelids.
The structure of the Central Finland synclinal zone is very complex. In addition to plutons, large faults play an important role in its tectoorogeny.
Proterozoic folded structures in the western part of Finland and Sweden are distinguished under the name Svecofennidae, and in the southern part of Sweden and southeastern Norway - Gothyd.
In southwestern Finland, the Svecofennids and Karelids articulate in the region of the Central Finland Massif. The latter is a structure similar to the Belomorian massif.
The structure of svecofennids is dominated by graywacke schists, leptites, which are metamorphosed volcanic rocks, volcanic rocks with a total thickness of about 8000 m. The base of these formations is unknown. A characteristic feature of sphecofennids is folded, strongly compressed structures and plastic flow structures in granitization zones. The strike of isoclinal folds is predominantly northwestern, changing in the areas of articulation with massifs.
From east to west and south, the main structural elements of the svecofennids are: the marginal zone of the svecofennids of northern Norland, which articulates with the Karelids in the east; in the south it includes the Skellefte anticlinorium, to the south it is delimited by faults: the synclinal zone of svecofennids of central Norland, the marginal zone of svecofennids of southern Norland, in the southwest bordering on the Värmland granite massif, and in the south it includes the anticlinorium of svecofennids and the synclinorium of Lake. Melaren, according to which the svecofennids articulate with the gotids.
The Gotids occupy the entire Precambrian region of southern Scandinavia - southern Sweden and the southeastern part of Norway. This entire part of the Baltic Shield is distinguished by a very complex structure of different ages and a different composition of strongly deformed rocks. In its structure, especially great importance have grandiose ancient faults.
Gneisses, granite-gneisses, mica schists, crystalline limestones, quartzites, conglomerates, etc. take part in the structure of the Gotids. In the structure of the Precambrian of southern Scandinavia, separate regions are distinguished, delimited by faults and grabens of submeridional strike. Particularly important tecto-orogenic importance is the fault zone of the lake. Vetter, stretching from the Baltic Sea to the borders of Norway and further north to Lake. Femunn. To the east of this zone lie: the Värmland granite massif, further to the southeast the Smaland granite massif and the Blekinge anticlinorium adjacent to it in the south, composed of gneisses. To the west of the Vetter Fault Zone extend almost in a meridional direction massifs of pre-Gothic and gray gneisses of southwestern Sweden. In the west, these structures are cut by the Oslo graben.
To the west of the Oslo graben there is a vast region of granite gneisses in southern Norway. In its eastern part, there is the Kontsberg-Bamblé massif, composed of sedimentary-metamorphic and igneous rocks. To the south-west of it is the equally complex Granit Telemark complex. In the northern part of the main region of the Precambrian of southern Norway, there is a sequence of folded sedimentary-metamorphic deposits about 4000 m thick.
In the structure of the tectonic relief of the crystalline basement of the Baltic Shield, the composition and structure of the ancient platform cover play an important role. Its remains have been preserved in some synclinal troughs, on different parts of the shield. Usually, the relics of the platform cover are composed of sedimentary, weakly metamorphosed rocks of iotnium and cambrosilur.
In the West Onega, Satakunta and other grabens, these deposits are represented by Potnian quartzite-sandstones, clay shales, siltstones, etc. the youngest deposits of the Precambrian are known in the graben of the lake. Vättern, where they are represented by arkosic sandstones and overlying shales. Cambrian-Ordovician deposits are common in the grabens of Västergötland and Ostergötland (the region of lakes Vänern and Vättern). They include sandstones, quartz shales, bituminous limestones, etc.
In the tectoorogeny of the Baltic Shield, the Oslo graben stands out as a separate structural complex. From the Oslofjord, the graben extends to the north, northeast of the quartzite cover of the Scandinavian mountains. The amplitude of the graben along the eastern coast of the Oslo Fjord is 2000-3000 m. It is made up of sandstones, shales and limestones of the Cambrian-Silurian age. In the northern part of the graben, these deposits form east-northeast folds; in the southern part, Paleozoic deposits contain intrusions of Permian alkaline rocks. Prior to this, the Paleozoic deposits were flattened, in the Early Permian they were overlain by continental deposits and basaltic sheets. Later, the intrusion of dikes and plutons of monzonite larvikites, syenite nordmarkites, etc., followed. Characteristics the structures of this graben are calderas formed along ring faults and linearly elongated stepped faults.
scandinavian highlands. Caledonides. The Scandinavian, or Caledonian, mountains are the most ancient folded structure in the western part of the Eurasian massif of the continental crust. In the course of the history of geological development, the vast region of the Caledonides was divided into separate blocks, a significant part of which sank below the level of the Atlantic Ocean. The surviving areas of the Caledonides represent the border of the East European Platform on the eastern coast of the Atlantic Ocean and the Greenland and Canadian shields- on the west. Significant isolated areas of the Caledonian structures are the islands of Svalbard, Jan Mayey, Bear, Faroe Islands, the tectonic connection of which with the marginal mountain structures of the Caledonides is still not clear enough.
The Caledonian border of the East European Platform is represented by the Scandinavian Mountains and the Caledonian Mountains (in the British Isles). Conventionally, this border also includes the Svalbard Caledonides, articulated with a fragment of the Precambrian island massif - part of the Baltic Shield or the hypothetical Baronets Sea Plate - constituent elements Precambrian structure of the East European Platform. The mainland and insular parts of the Caledonian formations have similar features in the structure of the tectonic and climatic, in particular glaciogenic, relief.
The Scandinavian mountains are an integral part of the physical and geographical region of the Scandinavian highlands. To a large extent, they have lost their primary tectonic relief. General peneplenization in the Cretaceous - Paleogene time, fault tectonics and recent movements, together with superimposed surface forms, gave the landscapes of the Precambrian and Caledonian parts of Scandinavia a lot in common. Therefore, keeping in mind the difference in structures, age, and history of development, we consider it expedient to jointly consider the tectoorogeny of the Baltic Shield and the mountains bordering it. The Caledonides of Scandinavia stretch along the outer edge of the peninsula from the Barents to the North Sea at a distance of over 1700 km. In the direction of the Atlantic Ocean, the abraded mountains form a shelf, in places reaching 250 km wide and plunging to a depth of 400 m.
Let us briefly consider the geological structure of the Caledonides. The foundations of the mountains are made up of Precambrian rocks of the Baltic Crystalline Shield. In the folded zone, the foundation in some places protrudes in the form of windows or separate arrays. The platform cover is composed of strata of pre-Devonian terrigenous deposits. These include the sparagmite complex of coarse clastic rocks. In the eastern part of southern Norway, Finmarken and other places, the lower part of the complex is represented by sandstones and shales. In the upper part of it, strata of tillite, quartz sandstone and clayey rocks are distinguished, overlain by sediments containing Late Cambrian fossils.
In the northwest of the country and in the ancient geosynclinal zone, the Cambrian-Silurian deposits are represented by effusive and intrusive rocks. In the folded regions of southern Norway, the following are distinguished in the composition of sedimentary deposits: Oslo facies - knotty limestones, shales and sandstones of the Oldred type; marine deposits of the Trondheim region, including shales with sandstones, conglomerates and a thick basalt (underwater) sequence, as well as sequences of basic extrusive rocks; Norland facies - metamorphic rocks, mainly mica schists, crystalline limestones and dolomites.
In the Caledonides of Sweden, the following rocks lie on the crystalline Precambrian basement (Tectonics of Europe, 1963): Eocambrian - quartzites and slates; Ordovician - slates and shale, greywackes, crystalline limestones containing strata of volcanic rocks; Silurian - shales, limestones, quartzites, conglomerates and thick strata of basic volcanic rocks. These deposits are highly dislocated. The structure of the Caledonides of the Scandinavian Highlands is determined by complex folding, cover and fault tectonics. Numerous intrusions of igneous rocks are known in the intensely folded structure.
The main features of the Caledonian tectoorogeny create nappes. Their front stretches along the entire Scandinavian Peninsula. The hinterland of the mountains form a huge tectonic cover of Seva. Its frontal part stands out as an independent cover composed of granites and syenites. The middle part of the Seva cover, also independent, is composed of slates, dolomitic marbles, quartzites, and arkose sandstones. These rocks include dikes and sills of basalt, which formed in the pre-cover phase. central part The Seva cover is composed of garnet gneisses, highly metamorphosed rocks that arose from mudstones, limestones and amphibolites, which were part of the crystalline basement. These sequences are overlain by the Köli shale of the Cambrian-Silurian age. The entire rock mass of the Seva cover is intruded by granites, gabbro, basalts, etc. The Caledonide covers piled one on top of the other from west to east.
In the final phases of the Caledonian orogeny in the southern part mountain country horst, arched uplifts arose in the outer zone of overthrusts. Their eastern front parts are disturbed by normal faults and complicated by secondary overthrusts and overlying folds. These structures seem to be syntectoic for the younger nappes of southern Norway, thrust over older, similar Caledonian structures.
In the Caledonides of Scandinavia, separate tectonic regions are distinguished from north to south by structural features: the Varanger Peninsula, the South Porsanger Peninsula, the Precambrian Porsanger Peninsula, the Ofoten syncline, the Lofotei eruptives, the Rombak window, the Nazafjell window, the Quartzite cover, the Sparagmite threshold, the Trondheim anticlinorium , areas of sparagmites and gneisses, covers of Pot and. Each of the tectonic regions is distinguished by the peculiarities of the structure and composition of the strata that compose it, one way or another reflected in the relief.
On Svalbard, the Caledonides occupy western part archipelago. They are articulated with the Precambrian basement of eastern Spitsbergen by a tectonic suture. Sedimentary deposits deposited on the island take part in the structure of the Svalbard Caledonides Northeast Land on gneisses crumpled into latitudinal folds. These deposits coalesce into the Hekla Hook Formation. Shales, quartzites, dolomites, conglomerates, tillites predominate in its composition. In the western part of the archipelago, the thickness of the Gegla-Khuk stratum is about 16,000 m. It includes thick volcanogenic strata.
The rocks of the Hekla-Khuk series are collected in linearly elongated meridional folds overturned onto the platform and complicated by overthrusts. Large structures are the New Friesland anticlinorium, which stretches for 150 km, the Hinlopen Strait synclinorium, the Cross Fjord anticlinorium, and others. All of these deposits to the south of the archipelago are covered by a cover of Upper Paleozoic and Mesozoic deposits. In their composition, Lower Carboniferous deposits with interlayers of coal are known. In western Svalbard, they form a large trough (from southeast to northwest). In the center of the trough there is a depression filled with conglomerates, sandstones and clays of the Tertiary age with thick layers hard coal. The thickness of these deposits is about 2000 m. Traps and traces of volcanic activity in the Mesozoic are widespread in the eastern part of the Svalbard archipelago. The Caledonian folding on Svalbard ended in the Silurian. Intrusions of Caledonian granites are known on the island.
The Caledonides of the British Isles occupy the predominant part of them. Folded structures protrude to the surface here and are covered by a cover of Paleozoic and Cenozoic deposits. The Caledonides of the islands are squeezed into the frame of the Precambrian, in the northwest - by a fragment of the Erne platform, in central England - by the ledge of the East European platform. In the south of England and Ireland, the Caledonides border on the Variscides.
The crystalline basement of the Aria platform is exposed in the northwest of Scotland and the Outer Hebrides. The Precambrian basement of the East European Platform can be traced in the southeastern part of England north of the Hercynide zone. The frame of the Caledonides of Britannia was a single platform in the Precambrian, extending westward in the Atlantic Ocean to the continental slope. In the Late Precambrian, a ditch-shaped subgeosynclinal trough was formed in the marginal part, in the modern structure it is occupied by folded Early Paleozoic formations.
Folded Caledonian formations are developed in most of the territory of the Scottish, Northern Irish and South Scottish Highlands, in the Pennines and Cambrian Mountains, and the Central Plain of Ireland.
Various sedimentary deposits of the Lower Paleozoic take part in the structure of the Caledonides of Britain. Their total thickness in the axial part of the British Caledonides, in the South Scottish Highlands, apparently reaches 20,000 m. Their most important feature is great development migmatites and granites. In the Caledonides of the British Isles at the present time (Tectonics of Europe, 1963), metamorphic and non-metamorphic zones are distinguished. The first occupies the northwestern part of the country. In the southeast, it is separated from the non-metamorphic zone by a deep fault, or lineament, with which the Great Boundary Fault is associated. The metamorphic zone is characterized by alpine-type tectonics with highly developed covers. Its structure is most pronounced in the Scottish Highlands and Northern Ireland. In the Scottish Highlands, the metamorphic zone is represented by argillite rocks of the Late Precambrian age, overlain by shallow and deep water deposits with spilite lavas and greenstone intrusions. The age of these formations is from late Precambrian to late Cambrian.
The dislocations of the metamorphic zone took place in two phases: in the Early or Middle Ordovician and the Middle Silurian. The folds have undergone repeated crushing with the development of overlying folds and integuments. The movement was directed to the outer sides - to the northwest and southeast. In the northwest, the Moin cover is developed, southeast of which the large Grant Glen Fault passes. The foreland underthrust under the dislocated masses is 120 km. A large cover of Loch Tay is developed on the southeastern edge of the metamorphic zone. The recumbent wing of this cover is exposed along southern border Scottish highlands. Extensive fields of migmatization and granite intrusions are developed in the Grampian Mountains.
In the southern part of the metamorphic zone, the large graben of the Midland Valley is filled with young sediments, under which the junction of metamorphic and non-metamorphic zones is hidden.
In the non-metamorphic zone of the Caledonides, three structural floors are distinguished. The lower one in the Midland graben, southwestern Scotland and northern Ireland is composed of a spilite complex. The middle structural stage forms the Southern Highlands. It includes the Upper Ordovician and Silurian. Its thickness is 10,000 m. It is characterized by early Devonian granodiorite intrusions. Their massifs are exposed in the western part of the South Scottish Highlands. The middle structural stage of the non-metamorphic zone also includes strata of ancient red sandstone. It was deposited in the ancient depressions of northern Scotland, the Midland graben and the Orkney Islands, accompanied by intense andesitic and basaltic volcanism.
Sedimentary sequences form a series of flexures separated by parallel normal faults. Their structure is complicated by isoclinal, overturned folds.
The complex structure and diverse lithological composition of the Caledonides determine the tectonic relief of the British Isles.
East European platform. Borders. Geological structure.
Borders
The problem of the position of the boundaries of the East European Platform has not yet been unambiguously resolved, and there are different points of view on it.
The map shows the top floor plan of the platform, which is reduced in area.
The nature of the borders is discordant (the platform was part of Pangea), in reality the border passes through the zones of tectonic faults.
The position of the eastern boundary of the platform is most definitely at present.
East platform frames the Ural fold belt 2200 km
(Permian marginal trough), the foundation penetrates part of the Urals, is cut off by a tectonic fault, i.e. in reality, this border is located at 150 km east of that that's on the map.
In the north-east the Timan-Pechora structure adjoins the platform - a rejuvenated basement (Baikal tectogenesis): it contains relics of an ancient basement - the boundary is drawn along the Urals to the coast; or we completely exclude this structure (according to Milanovsky).
In the north Atlantic Ocean - cont. / oceanic. bark, i.e. includes the shelf up to the Baltic Shield with the Caledonian structures of Scandinavia, which are pushed onto the platform with A = 150-120 km, than on the map to the northwest.
As western border the folded structure of the Carpathians is assumed - the Pre-Carpathian foredeep, the boundary is not real, passes to the west than shown on the map. Moved to VEP. In this area, the super-young platform articulates with the super-old one and forms a giant shear sheet. The Carpathians are a skibian structure.
On South- the border is curvilinear, it passes through the region of the mountainous Crimea (short shelf), includes the Sea of \u200b\u200bAzov, then goes around the Caucasus, the Scythian Plate, reaches the Caspian depression. There is no crystalline basement crust in the axial part of the Caspian syneclise. Therefore, we take only half of the syneclise, one side, but this is not possible, therefore we take the entire structure. (the thickness of the sedimentary cover is 20-25 km, there is no II layer of granite-metal) includes ½; then it goes along the entire coast of the Northern Caspian, the Southern Caspian is not included, then the border reaches the Southern Urals.
Geol. Structure
The geological structure of the East European Platform began in the first half of the 19th century. During its study, for the first time, such types of tectonic elements of ancient platforms as: shields, plates, anteclises, syneclises, aulacogens were identified and named.
1. Shields - Baltic, Ukrainian.
Voronezh massif (without cover)
2. Cover - syneclises:
Moscow, Glazov, Black Sea, Caspian,
Polish-Lithuanian, Baltic
Anteclise:
Belarusian, Voronezh, Volga-Ural
3. Intermediate sheath - a series of aulacogens:
Moscow, Abdullinsky, Vyatsko-Kama, Lvov, Belomorsky (at the base of the syneclise)
Dnieper-Donetsk aulacogen - Pz structure of the sedimentary cover
It is located between the Voronezh and Ukrainian shields. Before D was a Sarman shield. Now they say that this is an intracratonic geosyncline or rift. According to its structure, it is not similar to syneclise and therefore we attribute it to aulacogen.
The East European Platform corresponds to one of the largest continental blocks of Eurasia and belongs to the belt of ancient Laurasian platforms, which also includes the Siberian and North American platforms. It is a diamond-shaped continental block about 3000 km across, the base of which was formed about 1.6 billion years ago.
Two main types can be distinguished in relations with the uneven-aged fold-and-thrust structures surrounding the platform. So the Urals and the Carpathians are separated from the platform by their forward troughs superimposed on the lowered edges of the platform, and the Scandinavian Caledonides and the Baikal folded structures of the Timan directly overlap the autochthonous complexes of the platform along the thrust system, and the ridges can reach more than 200 km. However, traditionally, in both cases, it is customary to consider the front of the thrusts beyond the boundaries of the platform. In the remaining parts of its perimeter, the East European Platform borders on young plates - the Central European in the west, the Scythian-Turan in the south, and these limits are also represented by faults, partly subvertical, partly thrust. The southeastern corner of the platform is occupied by the Caspian Basin with a suboceanic type of crust, which is traditionally included in the platform. The boundary in this section of the platform is usually drawn along the buried South Emben dislocation zone. The depression is a relic oceanic basin filled with sediments up to 20 km thick. and its inclusion in the East European Platform, in this case, is very conditional. To the west, the modern boundary of the platform acquires a clearer character - it runs along the Paleozoic thrust of the Donetsk-Caspian fold zone, goes around the Donetsk Ridge and, turning to the west, crosses the Sea of Azov and the Black Sea and docks with the Teyser-Tornquist strike-slip zone.
The Precambrian crystalline basement is exposed mainly along the northwestern periphery of the East European Platform - the Baltic Shield, and also in the south - within the Ukrainian Shield. In addition, the structures of the crystalline basement of the platform include submerged massifs - the Voronezh and Volga-Urals, most of which are covered by platform sediments up to 1.5 km thick. These tectonic units have a pronounced large-block structure. So in the structure of the Ukrainian shield, five are distinguished, and the Baltic - six blocks, separated by deep faults or seams along which they were soldered. Each of the blocks has an individual internal structure, and often a material composition that is disharmonious with adjacent tectonic units. On the Baltic Shield stand out: Murmansk, Kola, Belomorsky, Karelian, Svekofensky and Svekonorwegian blocks. The Ukrainian shield is also formed by several blocks: Volyn-Podolsky, Odessa-Belotserkovsky, Kirovograd, Prydniprovsky, Pryazovsky. It can be assumed that similar blocks form the structure of the Voronezh and Volga-Ural massifs.
The oldest (AR 1) basement formations are granulite-gneiss areas composed mainly of rocks of the granulite facies of metamorphism. Apparently, among them there are protocontinental massifs formed on the original crust of the oceanic type, the relics of which are tonalites, ultramafic rocks and other rocks with an isotopic age of 3700 to 3100 Ma. The Murmansk and White Sea blocks of the Baltic Shield should be included in the group of essentially granulite blocks. The most typical rocks of their constituents are high-alumina biotite gneisses; metamorphosed "mature" sedimentary rocks, and metamorphosed volcanics of mafic composition, including amphibolites and charnockites (hypersthenic gneisses). The development fields of the described metamorphites are characterized by large granite-gneiss domes. They are rounded or elongated in one direction, tens of kilometers in diameter. Plagiogranite-gneisses and migmatites are exposed in the cores of the domes.
On the territory of the Kola and Karelian blocks of the Baltic Shield, as well as on most of the Ukrainian Shield, greenstone belts are "squeezed" between similar granite-gneiss domes. The composition of greenstone belts is fairly similar for most ancient platforms. The lower parts, as a rule, are composed of strata of basic effusives of spilite-diabase composition, sometimes significantly metamorphosed. The pillow structure indicates the outpouring of these mafic rocks under underwater conditions. The upper parts of the section are often represented by acid effusives - keratophyres, felsite, with interlayers of quartzite sandstones and gravelstones. According to the petrochemical characteristics, these metavolcanites in most cases correspond to MOR basalts and basaltic komatiites, however, sometimes metamorphosed calc-alkaline volcanic rocks of basalt-andesite-dacite composition are widely found in the greenstone belts. The structural position of the greenstone belts unequivocally testifies in favor of the fact that they are nothing more than the seams of the collision of various blocks of the most ancient crust. Stratigraphic contacts with the surrounding granulite-gneiss complexes are not observed anywhere, they are either shaded during later joint metamorphism, granitization and deformation of both complexes, or tectonic. AT last case greenstone belts are either narrow, highly compressed synclines bounded by faults, or rather isometric remnants of tectonic covers thrust over the granulite-gneiss base, which are preserved in the spaces between the domes. Isotope-geochronological dating allows us to consider that the formation of granite-greenstone areas on the territory of the East European platform occurred in the interval of 3100 - 2600 million years. There is no unambiguous point of view on the geodynamic nature of greenstone belts. They are associated with the subsidence and reworking of the primary sialic crust above the rising mantle diapira, or they see an analogy with modern rifts that "cracked" the protocontinental granulite-gneiss crust, or they are compared with the modern system of island arcs and marginal seas.
The Svecofennian block has absolutely individual structural features in the composite structure of the Baltic Shield. It is a typical representative of gneiss-shale areas. The most significant distinguishing features are: the absence of an Archean foundation; wide development of shale and gneiss-shale strata of the Early Proterozoic age, as well as large granitoid plutons, intruded in the range of 1850-1700 million years ago. A significant role in shale sections belongs to metavolcanics of both basic and felsic composition. In their structure, the complexes that make up the Svecofennian block are close to the gravuaco-volcanic series of Phanerozoic folded belts that formed in marginal seas separated by island arcs. Thus, the Svecofennian block can be interpreted as being formed as a result of accretionary tectonics. Granites, ubiquitous in the territory of the block, are an indicator of collisional processes, as a result of which the svecophenides were obducted and thrust onto the Karelian basement with the formation of an extended (almost 1500 km long) West Karelian thrust zone, "cutting off" the contours of the Kola-Karelian Archean-Proterozoic superterrane. The outcrops of the Lower Proterozoic (1.9 Ga) ophiolite complex gravitate to the zone of this thrust, indicating the formation of the Svecofennian belt on the oceanic-type crust. On the western periphery of the Svecofennian block, the Gotha (Trans-Scandinavian) volcano-plutonic belt is developed, composed of magmatites of mantle origin. Most notable in the belt are terrestrial felsic lavas, including rhyolites, dacites, ignimbrites, as well as lavas of increased alkalinity interspersed with agglomerates and arkoses. The effusives are associated with granite batholiths. The age of lavas and granites breaking through them is estimated at 1750-1540 million years. The composition and structure of this Proterozoic volcanic-plutonic belt is very similar to the continental marginal belts of the Andean type. Taking into account this analogy, it can be assumed that the Gothic belt in the Proterozoic occupied a marginal position and was formed above the subduction zone.
The composition and structure of the westernmost tectonic unit of the Baltic Shield, the Svekonorwegian block, is also highly individual. In terms of its structure, history of development, and time of final cratonization, this tectonic element is close to the Grenville orogenic belt of North America and is considered as its eastern continuation. The time of formation of the most ancient rocks of the Svekonorwegian zone corresponds to the interval of 1.75-1.9 billion years. They underwent significant reworking during the epoch of the Gothic (at the level of 1.7-1.6 billion years) and Dalsladian - Sveconovergian (1.2-0.9 billion years) orogeny. Internal structure The block is notable for its considerable complexity and actually represents a collage of cratonic, island-arc, etc. terranes. The metamorphosed volcanic-sedimentary and terrigenous sequences of the Early-Middle Proterozoic are most widely developed in varying degrees.
In general, the outcrops of the Early Proterozoic complexes of the Baltic and Ukrainian shields gravitate towards the suture zones delimiting the Archean blocks and, in contrast to the latter, have a more diverse composition and structure.
In the east of the Kola block, near the suture zone, the Lower Proterozoic deposits fill the Keivsky synclinorium and are represented by a series of the same name, unconformably overlying Archean gneisses. The Keivy Group is filled with sediments typical of a passive continental margin: at the base there are conglomerates with fragments of Archean rocks, then a thick sequence of high-clay shales and paragneisses, and at the top - arkose sandstones, as well as interlayers of dolomites, including stramotalites. The age of the granites breaking through the series is 1900-2000 million years.
The Proterozoic of the suture zone of the Kola and White Sea blocks (Pechenga and Imadra-Varzug zones) is similar in structure and composition to the Phanerozoic ophiolite belts. The vast majority of the section is made up of effusives of the main, in lesser degree medium and ultrabasic compositions. Many lavas have a cushion structure. Among the lavas there are horizons of conglomerates, arkoses, and quartzites containing fragments of Archean gneisses and granites. The section is saturated with ultramafic, gabbro, gabbronorite, and anorthosite bodies. The probable age of the rocks is 1900-1800 million years, the age of metamorphism is 1800-1700 million years.
The Early Proterozoic complexes of the East Karelian suture zone located between the Karelian and White Sea blocks are geodynamically associated with subduction processes. These formations are described as part of the Sumian complex. The age of the deposits is 2400 million years. In general, the complex is formed by two types of deposits - volcanogenic (Tungut series), which are characterized by a continuous series from basalts through andesites to rhyolites, and detrital (Sarioli series). The Sumium of the Karelian Block was subject to folding, metamorphism, and was intruded by plagiogranites with an age of ~2000 Ma.
In internal parts Archean blocks from the turn of ~ 2.3 billion years (Seletska folding), the appearance of essentially terrigenous sediments of the protoplatform cover is noted. The section of this complex is represented by three strata: jatulium - quartz conglomerates, gravelstones, sandstones interbedded with rare covers of basalts; suisariy - clay shales, phyllites, dolomites with interlayers of tholeiitic basalts; Vepsian - conglomerates and sandstones with gabbro-diabase sills.
On the Ukrainian Shield, the famous Krivoy Rog series, containing rich deposits of jespelite ores, belongs to the Early Proterozoic. It is localized mainly along the Krivoy Rog zone on the border between the Dnieper and Kirovograd blocks, as well as along the Orekhovo-Pavlograd zone, which limits the Dnieper and Azov blocks, forming narrow fault synclinoria. A complete analogue of the Krivoi Rog series is the well-known Kursk series of the Voronezh massif. Absolute age of these deposits falls into the interval of 2500-1880 million years. The section is represented by three strata from bottom to top: essentially detrital (quartzite-sandstone, conglomerate, phyllite, graphite schist); flysch-like (rhythmic alternation of jespelites and cherts); terrigenous (conglomerates, gravelstones, quartzites). The total thickness is 7-8 km, all deposits are intruded by granites with an age of 2.1 - 1.8 billion years
The foundation of the East European Platform is broken by narrow, deep (up to 3 km or more) graben-like troughs (aulacogens) - dead rays of the ancient rift systems. In the history of the development of the platform, three main epochs of graben-formation are outlined: Riphean, Devonian and Permian (Oslo graben).
Riphean aulacogens are the most numerous. They form an almost rectangular network of northeast and northwest directions and break the foundation of the platform into a series of blocks roughly corresponding to shields and submerged massifs. The longest (at least 2000 km) is a system of northeastern grabens, extending from the western end of the Ukrainian shield to the junction of the Timan with the Urals and consists of two independent aulacogens: Orsha-Volyn-Kresttsovsky in the west and Sredne-Russian in the east. From the place of their junction to the southeast, the Pachelma paleorift departs, and to the northwest, less clearly defined, the Ladoga. The Kandalaksha and Mezen grabens approach the Middle Russian aulacogen almost at a right angle from the north. In the very east of the platform, on the Volga-Ural arch, there is the Kaltasinsky aulacogen. The grabens-filling complexes are dominated by Middle Riphean red-colored coarse clastic strata formed due to erosion of nearby uplifts. Often, thick (up to 400 m) lava covers of basalts, tuffs, volcanic breccias, and dolerite sills appear at the base of the section. Of the igneous complexes, bimodal alkaline-ultrabasic series with carbonatites are characteristic. Higher in the section, the Riphean volcanic-terrigenous formations are replaced by Vendian shallow-marine sediments, the strata of which pass from the grabens to the adjacent basement blocks, which indicates that large areas of the platform were involved in the subsidence, the formation of sedimentary basins, and, as a result, the beginning of the accumulation of the platform cover.
The second epoch of continental rifting is associated with the emergence of the Pripyat-Dnieper-Donetsk aulacogen, as well as a series of grabens along the eastern margin of the platform. The formation of the Dnieper-Donetsk rift separating the Ukrainian and Voronezh massifs occurred at the end of the Middle - Late Devonian and was accompanied by intense magmatism: outpourings of alkaline basalts, the intrusion of alkaline-ultrabasic intrusions. The Upper Devonian is characterized by evaporites, which mark the subsidence of the paleorift and its connection with the sea basin. In the Carboniferous, this area was a place of accumulation of thick strata of parallic coals (Donbass), and at the end of the Permian, its eastern part underwent intense deformations as a result of the convergence of the Ukrainian and Voronezh shields. Terrigenous sedimentation within the aulacogen continued throughout the Late Paleozoic and into the Mesozoic.
Most of the platform, with the exception of the shields, is covered by the Phanerozoic sedimentary cover. Its formation took place in three stages, directly related to the stretching of the basement and the development of the surrounding oceans.
The Vendian-Lower Paleozoic complex composes: a strip that crosses but diagonally the East European Platform and separates the Baltic Shield from the southern crystalline massifs (Moscow syneclise); a strip along the Teiseira-Tornquist line (Baltic syneclise) and a strip stretching along the Timan (Mezen syneclise). Sedimentary basins of this time formed either above the Riphean aulacogenes or along the passive margins of the East European continent. The composition of the Vendian-Lower Paleozoic platform complex is represented by shallow sandy-clayey, and in the upper (Ordovician-Silurian) - carbonate sediments with evaporites. Of no small importance is the wide development of tillites, characteristic of the early Vendian, which indicates a sheet glaciation.
The Middle-Upper Paleozoic complex in places inherits earlier depressions, as in the Moscow syneclise, but the main volume of the cover is concentrated on the eastern and southeastern margins of the platform and in the region of the Dnieper-Donetsk aulacogen. To the south and southeast of the platform complex for the most part begins with the Middle Devonian. The formation of extensional structures - Devonian grabens - is associated with the initial periods of its formation. The most complete section (from the middle Ordovician to the Lower Carboniferous) is characteristic of the eastern margin of the platform, where it is involved in the nappe-thrust dislocations of the western slope of the Urals. In its composition, it can be confidently compared with the sediments of passive continental margins. Most notable for the complex under consideration are carbonate sediments, including reef facies, numerous in the Early and Late Devonian, Carboniferous, and Early Permian. The Late Devonian is characterized by the distribution of clay facies, saturated organic carbon. Their accumulation is associated with stagnant waters. In the Permian, due to the growth of the Urals and the thrusting of the ridges onto the platform, the sedimentary basin gradually dried up and salt-bearing strata formed. The result of this process was the formation of the Cis-Ural marginal foredeep, filled with a powerful red-colored molasse, a product of the destruction of the Ural Mountains.
The Meso-Cenozoic complex is developed only along the southern periphery of the platform: in the Caspian basin, in the Pripyat-Dnieper trough and the Black Sea basin. The sea penetrated beyond this strip only in narrow tongues in the Late Jurassic and Early Cretaceous, forming thin strata of sediments. The complex is dominated by terrigenous strata; writing chalk accumulated only during the period of maximum transgression in the Late Cretaceous. The thickness of the complex is small, only occasionally exceeding 500 m.
EASTERN EUROPEAN PLATFORM
Selection history
In 1894, A.P. Karpinsky for the first time singled out the Russian plate, understanding it as part of the territory of Europe, characterized by the stability of the tectonic regime during the Paleozoic, Mesozoic and Cenozoic. Somewhat earlier, Eduard Suess in his famous book "The Face of the Earth" also singled out the Russian plate and the Scandinavian shield. In Soviet geological literature, plates and shields began to be considered as constituent units of larger structural elements of the earth's crust - platforms. In the 1920s, G. Stille used the term "Fennosarmatia" to designate this platform. Later, A. D. Arkhangelsky introduced the concept of the "East European platform" into the literature, indicating that shields and a plate (Russian) can be distinguished in its composition. This name quickly entered into geological use, and is reflected on the latest International Tectonic Map of Europe (1982).
When, at the end of the last century, A.P. Karpinsky first summarized all the geological data on European Russia, there was not a single well on its territory that reached the foundation, and there were only a few small wells. After 1917, and especially after the Great Patriotic War, the geological study of the platform advanced at a rapid pace, using all the latest methods of geology, geophysics, and drilling. Suffice it to say that at present there are thousands of wells in the European part of the USSR that have penetrated the foundation of the platform, and there are hundreds of thousands of shallower wells. The entire platform is covered by gravimetric and magnetometric observations, and DSS data are available for many areas. Recently, satellite images have been widely used. Therefore, at present we have a huge new factual geological material, which is replenished every year.
Platform boundaries
The boundaries of the East European Platform are extremely sharp and clear (Fig. 2). In many places, it is limited by straight-line zones of thrusts and deep faults, which N. S. Shatsky called marginal sutures or marginal systems separating the platform from the folded structures framing it. However, not in all places the boundaries of the platform can be drawn with sufficient confidence, especially where its edge sections are deeply submerged and the foundation has not been penetrated even by deep wells.
The eastern boundary of the platform is traced under the Late Paleozoic Cis-Ural foredeep, starting from Polyudov Kamen, through the Ufimskoe plateau to the Karatau ledge up to the interfluve of the Ural and Sakmara rivers. The Hercynian folded structures of the Western slope of the Urals are thrust towards the eastern edge of the platform. To the north of Polyudov Kamen, the boundary turns to the northwest, runs along the southwestern slope of the Timan Ridge, further to the southern part
Rice. 2. Tectonic scheme of the East European Platform (according to A. A. Bogdanov, with additions):
1 - protrusions on the surface of the pre-Riphean basement (I - Baltic and II - Ukrainian shields); 2 - isohypses of the basement surface (km), outlining the main structural elements of the Russian Plate (III - Voronezh and IV - Belorussian anteclises; V - Tatar and VI - Tokmovsky arches of the Volga-Ural anteclise; VII - Baltic, VIII - Moscow and IX - Caspian syneclises; X - Dnieper-Donetsk trough; XI - Black Sea depression; XII - Dniester trough); 3 - areas of development of salt tectonics; 4 - epibaikalian Timan-Pechora plate, outer ( a) and internal ( b) zones; 5 - Caledonides; 6 - hercynides; 7 - Hercynian marginal troughs; 8 - alpids; 9 10 - aulacogens; 11 - overthrusts, covers and direction of thrusting of rock masses; 12 - modern platform borders
Kanin Peninsula (west of the Czech Bay) and further to the Rybachy Peninsula, Kildin Island and Varanger Fjord. Throughout this space, the Riphean and Vendian geosynclinal strata are pushed over the ancient East European platform (in the Caledonian time). In favor of such a drawing of the boundary, geophysical data, indicating the continuation of the structures of the Riphean strata of the Northern and Polar Urals, the so-called preuralides, in a northwestern direction towards the Bolynzemelskaya tundra, force them to incline. This is well emphasized by banded magnetic anomalies, which differ sharply from the mosaic anomalies of the magnetic field of the Russian Plate. The magnetic minimum characterizing the Riphean shale
the Timan strata, also occupies the western half of the Pechora lowland, and its eastern half already has a different, striped, alternating magnetic field, similar, according to R.A. Gafarov and A.K. Ural 1 . Northeast of Timan, the basement of the Timan-Pechora epibaikal plate, represented by effusive-sedimentary and metamorphic rocks of the Riphean - Vendian (?), was uncovered by a number of deep wells.
The northwestern boundary of the platform, starting from the Varanger Fjord, is hidden under the Caledonides of northern Scandinavia thrust over the Baltic Shield (see Fig. 2). The thrusting amplitude is estimated at more than 100 km. In the area of Bergen, the platform border goes into the North Sea. At the beginning of our century, A. Tornkvist outlined the western border of the platform along the line of Bergen - about. Bonholm - Pomorie - Kuyavsky swell in Poland (Danish-Polish aulacogene), along this line there are a number of echelon-shaped breaks with a sharply lowered southwestern flank. Since then, this border has been called the "Tornquist Line". This is the "minimum" platform boundary. The boundary of the East European Platform (Tornquist line) in the area of about. Rügen turns west leaving the Jutland peninsula within the platform and meets somewhere in the North Sea with a continuation northern border platform following along the front of the overthrust Caledonides and out to the North Sea in Scandinavia.
From the northern outskirts of the Sventokrzysz Mountains, the platform boundary can be traced under the Carpathian marginal foredeep, to Dobruja at the mouth of the Danube, where it sharply turns to the east and passes south of Odessa, through the Sivash and the Sea of Azov, is interrupted east of Yeysk due to the entry of the Hercynian folded into the body of the platform. structures of Donbass and reappears in the Kalmyk steppes. It should be noted that in the place where the Carpathians in the south and in the north turn to the west, the platform borders on the Baikalides (Rava - Russian zone). Despite the general straightness of the boundaries of the platform in the Black Sea region, it is broken by numerous transverse ruptures.
Further, the boundary passes south of Astrakhan and turns to the northeast along the South Emba fault zone, which traces a narrow buried Hercynian trough (aulacogen), which merges with the Zilair Synclinorium of the Urals. This South Emba Hercynian aulacogen cuts off from the platform its deeply submerged block within Ustyurt, as suggested by the DSS data. From the Aktobe Cis-Urals, the platform boundary follows due south along the western coast Aral Sea up to the Barsakelmes trough, where it turns west almost at a right angle, along the Mangyshlak-Gissar fault. There is also an opinion that the basement in the North Ustyurt block is of Baikal age, i.e., in the southeastern corner of the platform, almost the same situation occurs as in the western corner, which is associated with the uncertainty of the age of the folded basement submerged to a considerable depth.
Thus, the East European Platform looks like a giant triangle, the sides of which are close to rectilinear. A characteristic feature of the platform is the presence of deep depressions along its periphery. From the east the platform is limited
hercynides of the Urals; from the northeast - Timan Baikalids; from the northwest - the Caledonides of Scandinavia; from the south - mainly by the epihercynian Scythian plate of the Alpine-Mediterranean belt, and only in the region of the Eastern Carpathians folded chains of alpid superimposed on the Baikalides and Hercynides closely adjoin the platform.
The ratio of the foundation and cover
The foundation of the platform is composed of Lower and Upper Archean and Lower Proterozoic metamorphic formations intruded by granitoid intrusions. The deposits of the Upper Proterozoic, in which the Riphean and Vendian are distinguished, already belong to the platform cover. Therefore, the age of the platform, determined from the stratigraphic position of the oldest cover, can be determined as Epi-Early Proterozoic. According to B, M. Keller and V.S. Sokolov, the upper part of the Lower Proterozoic formations, represented by gently lying strata of sandstones, quartzites and basalts, composing simple troughs, may also belong to the most ancient deposits of the cover of the East European Platform. The latter are often complicated by faults and in some places take the form of wide grabens. Areas with a Baikal basement should not be included in the ancient platform.
The oldest platform cover has some features that distinguish it from a typical Paleozoic platform cover. In different places on the platform, the age of the oldest cover can be different. There are two essentially different stages in the history of the formation of the platform cover. The first of them, according to A. A. Bogdanov and B. M. Keller, apparently corresponds to the entire Riphean time and the beginning of the Early Vendian and is characterized by the formation of deep and narrow graben-shaped depressions - aulacogens, according to N. S. Shatsky, poorly executed metamorphosed, and sometimes dislocated Riphean and Lower Vendian deposits. The emergence of narrow depressions was predetermined by faults and the structural pattern of the youngest folded basement zones. This process was accompanied by rather energetic volcanism. A. A. Bogdanov proposed to call this stage of development of the platform aulacogenous, and the deposits formed at this time should be identified as the lower level of the platform cover. It should be noted that most of the Riphean aulacogenes continued to "live" in the Phanerozoic, being subjected to folded Cadwig and block deformations, and volcanism also manifested itself in places.
The second stage began in the second half of the Vendian and was accompanied by a significant tectonic restructuring, expressed in the death of aulacogens and the formation of vast gentle basins - syneclises, which developed throughout the Phanerozoic. Deposits of the second stage, which in general can be called slab, form the upper level of the platform cover.
Foundation relief and modern platform structure
Within the East European Platform, as structures of the first order, Baltic and Ukrainian shields and Russian stove. Since the end of the Middle Proterozoic, the Baltic Shield has tended to rise. The Ukrainian shield in the Paleogene and Neogene was covered by a thin platform cover. Foundation relief
The Russian plate is extremely strongly dissected, with a span of up to 10 km, and in places even more (Fig. 3). In the Caspian depression, the depth of the foundation is estimated at 20 or even 25 km! The dissected character of the relief of the basement is given by numerous grabens - aulacogenes, the bottoms of which are disturbed by diagonal or rhomboid faults, along which there were movements of individual blocks with the formation of horsts and smaller secondary grabens. Such aulacogens are in the east of the platform Sernovodsko-Abdulinsky, Kazansko-Sergievsky, Kirovsky; in the center Pachelmsky, Dono-Medveditsky, Moscow, Central Russian, Orsha-Krestsovsky; in the north Kandalaksha, Keretsko-Leshukonsky, Ladoga; in the West Lvov, Brest other. Almost all of these aulacogens are expressed in the structure of deposits of the lower level of the platform cover.
In the modern structure of the Russian Plate, there are three large and complex anteclises stretching in the latitudinal direction: Volga-Ural, Voronezh and Belarusian(See Fig. 3). All of them are sections of the foundation, elevated in the form of complex extensive vaults, disturbed by faults, along which their individual parts experienced displacements of different amplitudes. The thickness of the Paleozoic and Mesozoic deposits of the cover within the anteclise is usually a few hundreds of meters. The Volga-Ural anteclise, which consists of several basement protrusions ( Tokmovsky and Tatar vaults), separated by depressions (for example, Melekesskaya), filled with Middle and Upper Paleozoic deposits. Anteclises are complicated by ramparts ( Vyatsky, Zhigulevsky, Kamsky, Oksko-Tsninsky) and flexures ( Buguruslanskaya, Tuymazinskaya and etc.). The Volga-Ural anteclise is separated from the Caspian Basin by a strip of flexures called "zones Peri-Caspian dislocations". Voronezh anteclise has an asymmetric profile - with a steep southwestern and very gentle northeastern limbs. It separates from the Volga-Ural anteclise Pachelma aulacogen, opening into the Caspian basin and the Moscow syneclise. In the area of Pavlovsk and Boguchar, the foundation of the anteclise is exposed on the surface, and in the southeast it is complicated Dono-Medveditsky rampart. Belarusian anteclise, which has the smallest dimensions, is connected to the Baltic Shield Latvian, and with the Voronezh anteclise - Bobruisk saddles.
Moscow syneclise It is a vast saucer-shaped depression, with slopes on the wings of about 2-3 m per 1 km. Polish-Lithuanian syneclise it is framed from the east by the Latvian saddle, and from the south by the Belarusian anteclise and can be traced within the water area of the Baltic Sea. In places it is complicated by local uplifts and depressions.
To the south of the anteclise strip there is a very deep (up to 20-22 km) Caspian depression, in the north and northwest clearly delimited by flexure zones; complicated Dnieper-Donetsk graben-like trough, separable Chernihiv ledge on the Pripyatsky and Dnieper troughs. The Dnieper-Donetsk trough from the south is limited by the Ukrainian shield, to the south of which is Black Sea depression filled with late Mesozoic and Cenozoic deposits.
Fig 3. Scheme of the relief of the foundation of the Russian plate (using the material of V. E. Khain):
1 - protrusions of the pre-Riphean foundation to the surface. Russian stove: 2- foundation depth 0-2 km; 3 - the depth of the foundation is more than 2 km; 4 - main discontinuous violations; 5 - epibaikal plates; 6 - Caledonides; 7 - hercynides; 8 - epipaleozoic plates; 9 - Hercynian foredeep; 10 - alpids; 11 - Alpine marginal troughs; 12 - thrusts and covers. The numbers in the circles are the main structural elements. Shields: 1- Baltic, 2 - Ukrainian. Anteclise: 3- Belarusian, 4 - Voronezh. Vaults of the Volga-Ural anteclise: 5- Tatar, 6 - Tokmovsky. Syneclise: 7- Moscow, 8 - Polish-Lithuanian, 9 - Caspian. Epibaikal plates: 10 - Timan-Pechora, 11 - Mysian. 12 - Folded structure of the Urals, 13 - Cis-Ural trough. Epipaleozoic plates: 14 - West Siberian, 15 - Scythian. Alpides: 16 - Eastern Carpathians, 17 - Mountainous Crimea, 18 - Greater Caucasus. marginal deflections: 19 - Precarpathian, 20 - Western Kuban, 21 - Terek-Caspian
The western slope of the Ukrainian Shield, which was characterized by a steady deflection in the Paleozoic, is sometimes distinguished as Transnistrian trough, merging into Lviv depression. The latter is separated Ratnensky ledge foundation from Brest depression, bounded from the north by the Belarusian anteclise.
Platform foundation structure
The Archean and partially Lower Proterozoic sediments that form the foundation of the East European Platform are strata of primary sedimentary, volcanic-sedimentary and volcanic rocks metamorphosed to varying degrees. Archean formations are characterized by very vigorous and specific folding associated with the plastic flow of the material at high pressures and temperatures. Structures such as gneiss domes, first identified by P. Escola in the northern Ladoga region, are often observed. The foundation of the platform is exposed only on the Baltic and Ukrainian shields, while in the rest of the space, especially within large anteclises, it has been exposed by boreholes and has been well studied geophysically. For the dismemberment of basement rocks, the data on determining the absolute age are important.
Within the East European Platform, the oldest rocks are known with an age of up to 3.5 billion years or more, which form large blocks in the basement, which are framed by younger folded zones of Late Archean and Early Proterozoic age.
Foundation outlets to the surface. The surface of the Baltic Shield is sharply dissected (up to 0.4 km), but exposure due to the cover of Quaternary glacial deposits is still weak. The study of the Precambrian of the Baltic Shield is associated with the names of A. A. Polkanov, N. G. Sudovikov, B. M. Kupletsky, K. O. Kratz, S. A. Sokolov, M. A. Gilyarova, and the Swedish geologist N. Kh. Magnusson , Finnish - V. Ramsey, P. Eskol, A. Simonen, M. Härme and many others. Recently, the works of A. P. Svetov, K. O. Kratz, and K. I. Heiskanen have been published. The Ukrainian shield is overlain by Cenozoic deposits and exposed much worse than the Baltic one. The Precambrian of the Ukrainian Shield was studied by N. P. Semenenko, G. I. Kalyaev, N. P. Shcherbak, M. G. Raspopova, and others. At present, a significant revision of the data on the geological structure of the Baltic and Ukrainian shields and closed territories Russian plate.
Archean formations. On the Baltic Shield in Karelia and on the Kola Peninsula, the oldest deposits come to the surface, represented by gneisses and granulites with an age (clearly radiometrically younger) of 2.8-3.14 billion years. Apparently, these strata form the foundation of the so-called belomorid, forming in Karelia and in the south of the Kola Peninsula a zone of northwestern strike, and in the north of the peninsula - the Murmansk massif. Belomorids in the composition Keret, Hetolambin and loukh suite in Karelia and tundra and lebyazhinskaya on the Kola Peninsula are represented by various gneisses, including aluminous (Lukh Formation), amphibolites, pyroxene and amphibole crystalline schists, diopside calciphyres, komatiites, drusites, and other primary sedimentary and volcanic rocks of basic and ultrabasic composition with numerous intrusions of various shapes. Highly metamorphosed strata form gneiss domes, first described by P. Escola near Sortovala, with a gently sloping, almost horizontal bedding of deposits in the arch and complex folding along the edges. The emergence of such structural forms is possible only at great depths under conditions of high temperatures and pressures, when the substance acquires the ability to plastic deformation and flow. Maybe gneiss domes "float" like salt diapirs. The absolute age values for Belomorids do not fall older than 2.4-2.7 billion years. However, these data undoubtedly give too young age of the rocks.
On the Lower Archean deposits of the Belomorids in Karelia, a stratum of Late Archean age occurs ( lopius), represented by ultrabasic (komatiites with a spinifex structure), basic, and less often medium and felsic volcanic rocks enclosing massifs of ultramafic and plagiogranites. The relationship of these protogeosynclinal deposits, more than 4 km thick, with the basement complex is not entirely clear. The supposed conglomerates at the base of the lobium are most likely blastomylonites. The formation of these typically greenstone deposits has ended rebolsk folding at the turn of 2.6-2.7 billion years.
Paragneisses and high-alumina shales are analogous to lopium on the Kola Peninsula. cave series, as well as variously metamorphosed rocks tundra series(in the southeast), although it is possible that the latter are products of diaphthoresis of older deposits.
On the Ukrainian shield the oldest Archean rock complexes are widespread, forming four large blocks, separated by faults from the Lower Proterozoic shale-iron ore sequences, which form narrow near-fault synclinor zones. Volyn-Podolsky, Belotserkovsky, Kirovogradsky, Dnieper and Azov blocks(from west to east) are composed of various Archean strata, and the Belotserkovsky and Dnieper blocks are amphibolites, metabasites, jaspilites Konk-Verkhovets, Belozersk series, i.e., rocks of primary basic composition, metamorphosed under conditions of amphibolite, sometimes granulite facies and resembling the deposits of the Baltic Shield lopium. The rest of the blocks are composed mainly of Upper Archean granite-gneisses, granites, migmatites, gneisses, anatectites - generally acidic rocks, in some places with relics of an ancient foundation.
On the Voronezh anteclise gneisses and granite-gneisses are the oldest rocks, analogues of Belomorids and Dneprids. Oboyan series. They are overlain by metabasites. Mikhailovsky series, apparently coeval to lopius and metabasites of the Dnieper Group (Table 2).
Lower Proterozoic formations platforms are relatively poorly developed in the basement, including on shields, and differ sharply from the most ancient Archean sequences, composing linear folded zones or isometric troughs. On the Baltic shield above the Archean complexes with a clear unconformity, strata sumia and sariolia. The Sumian deposits are closer to orogenic formations and are represented by terrigenous rocks and metabasites, closely associated with the Sariolian conglomerates located above, which can partially replace the Sumian sequences. Recently, above the lopium and below the sumium, K.I. suomiya, composed of quartzites, carbonates, siliceous and amphibole schists and apo-basaltic amphibolites, occupying a stratigraphic interval of 2.6-2.7 - 2.0-2.1 billion years, corresponding to the Sortavala series of the northern Ladoga region and the "marine jatulia" of Finland. Apparently, this also includes flyschoid deposits. Ladoga series, lying above Sortavala.
The Sumiy-Sariolian complex is an essentially volcanic stratum with conglomerates in the upper part, its thickness is up to 2.5 km. The predominantly primary basaltic, andesite-basaltic, and rarely more acidic volcanic rocks are associated with grabens, which, according to A.P. Svetov, complicated the large arched uplift. Sariolium conglomerates are closely associated with sumium structures, the latter being intruded by K-Na granites in northern Karelia.
After weak phases Seletska folding, which took place at the turn of 2.3 billion years, the region of the modern Baltic Shield enters
table 2
Scheme of subdivision of the basement formations of the East European Platform
a new stage of its development, already reminiscent of a platform. Accumulation of relatively thin strata yatuliya, suisaria and vepsia preceded by the formation of a weathering crust. Jatulium is represented by quartz conglomerates, gravelstones, sandstones, quartzites with traces of ripples and drying cracks. Sedimentary continental rocks are interbedded with covers of basalts. Suisari deposits are composed in the lower parts by clay shales, phyllites, shungites, dolomites; in the middle part - covers of olivine and tholeiite basalts, picrites, and in the upper part - sandstones and tuff shales again prevail. Even higher are conglomerates and polymictic Vepsian sandstones with gabbro-diabase sills (1.1-1.8 Ga). The total thickness of all these deposits is 1-1.2 km, and all of them, lying almost horizontally, are cut through by rapakivi granites (1.67 billion years).
Rice. 4. Schematic diagram of the relationships between the main complexes of Precambrian (pre-Riphean) formations on the Baltic Shield (in Karelia):
1 - protoplatform complex (Jatulian, Suisarian, Velsian) PR 1 2 ; 2 - proto-orogenic complex (sumium, sariolia) PR 1 1 ; 3 - protogeosynclinal complex (lopiy, suomiy?) AR 1 2 ; 4 - base complex (Belomorids and more ancient) AR 1 1
Thus, a rather definite sequence of pre-Riphean rock complexes is established in Karelia (Fig. 4). The base complex is represented by gray gneisses and ultrametamorphic strata of the Belomorids (Lower Archean). Above, there is a greenstone protogeosynclinal Lopian complex (Upper Archean), which is unconformably overlain by the prothorogenic Sumiya-Sariolium and the protoplatform deposits of the Jatulian, Suisarian, and Vepsian. A picture is outlined that is close to the Phanerozoic geosynclines, but very much extended in time.
Lower Proterozoic formations on Kola Peninsula represented imandra-varzug and Pechenga greenstone metabasite series with a weathering crust at the base, forming narrow (5-15 km) fault troughs enclosed between Archean blocks in the north and south, although it is possible that the northern Murmansk block is a thick (1 km) allochthonous plate thrust from the north to younger formations. The deposits were located at the end of the Early Proterozoic.
On the Ukrainian shield Lower Proterozoic is the famous Krivoy Rog series, forming narrow fault synclinoria superimposed on the Archean complexes, 10-50 km wide. The Krivoy Rog series is subdivided into the lower terrigenous sequence
Rice. Fig. 5. Geological profile of the ore band of the Yakovlevsky deposit, Voronezh anteclise (according to S. I. Chaikin):
1 - allites and redeposited ores; 2 - martite and iron mica ores; 3 - hydrohematite-martite ores; 4 - iron-mica-martite quartzites; 5 - hydrohematite-martite ferruginous quartzites with shale interbeds; 6 - conglomerates: 7 - phyllites of the ore shale suite; 8 - supraoral phyllites; 9 - thinly banded phyllites; 10 - faults
(quartzite-sandstones, conglomerates, phyllites, graphite shales); the middle one is iron ore, consisting of rhythmically alternating jaspilites and flysch-like shales; the upper one is mostly terrigenous (conglomerates, gravelstones, quartzites). The total thickness of the series is up to 7-8 km, its deposits are intruded by granites with an age of 2.1-1.8 billion years.
An analogue of the described formations on Voronezh anteclise deposits are also trinomial Kursk series with an iron ore sequence in the middle part, forming narrow synclinor zones oriented in the meridional direction and well traced in the magnetic anomalous field (Fig. 5). Younger terrigenous and metabasite deposits occur in the east of the Voronezh anteclise Vorontsov and Losevskaya series, which include fragments of jaspilites and a large number of stratiform intrusions of ultrabasites (Mamon complex), with copper-nickel-sulfide mineralization.
