On the Siberian platform, Cambrian deposits are much more widespread. As can be seen from fig. 48, they occupy a vast area in the north, in the basin of the Anabar, Khatanga, and Olenek rivers, covering here the surface of the Anabar Archean massif; a huge strip of them stretched along the western and southern edges of the platform from the Yenisei Ridge to Lake. Baikal and from here along the river. Lena on the Aldan plateau almost to the mouth of the river. Vilyuya; smaller areas are located along the lower reaches of the river. Yenisei and along the river. Vilyuyu. All of the sites listed are areas where the Precambrian basement is uplifted; intermediate areas - the central parts of the platform - are areas of deep trough-shaped troughs. Since the Cambrian deposits at the outcrops do not give any indication of wedging out towards the troughs, it must be assumed that the troughs at depth are also lined with Cambrian rocks. In other words, the Cambrian rock cover covers the entire Siberian platform. Separate scattered outcrops of Cambrian deposits inside the troughs, confined to small domes, confirm this conclusion.

The structure of the Cambrian deposits of the Siberian Platform is complex. It is convenient to start acquaintance with them with a section along the middle course of the river. Lena from the mouth of the river. Peleduya to the river. Blue.

At the base of the Cambrian stratigraphic column on the eroded surface of the Archean, there is usually a small plastic of a small-pebble conglomerate, in one place (the lower reaches of the Bolshoi and Maly Patom rivers) swelling into a significant thickness; it is followed by brick-red clays and marls, sometimes mute, sometimes with an abundant fauna of archaeocyaths (Sinya River). Above are limestones and dolomites, mostly white or gray, pinkish or greenish, sometimes massive, sometimes platy and thickly layered, sometimes brecciated. Most often, these limestones are paleontologically mute, but in some layers there are algae of the Collenia type, archaeocyates, less often trilobites and brachiopods; sometimes these organisms overflow the rock, forming archaeocyanate or algal reefs. These are undoubtedly marine and, moreover, very shallow-water formations, partly of the type of sheet-like coral reefs, partly of the type of calcareous silts of the modern Bahama Shoal. In the middle reaches of the river Lena from the river. Botomak to the river. Blue and along the river. In blue, black and gray bituminous limestones are developed, sometimes so enriched in organic matter that they turn into oil shale. In bituminous limestones, there are no longer any algae or archaeocyaths, but numerous trilobites (Agnostus, Protolenus), winged mollusks (Hyolithes) and primitive brachiopods are found. It is possible that these are deeper sediments compared to the light-colored algal and archaeocyanate limestones mentioned above.

The Middle Cambrian rocks throughout the described area are uniform and are represented mainly by light, white and gray limestones, similar to the Lower Cambrian. They also sometimes mute, sometimes contain an abundant fauna of archaeocyata, numerous and diverse trilobites (Agnostus, Apotosate, Ptychoparia, Dorypyge, etc.), brachiopods (Obolus, Lingula), accumulations of spherical and flat flaky secretions of algae (Collenia, etc.). In the upper horizons of the limestone strata, dolomitization is sharply manifested and interlayers of gypsum are found in places.

The Upper Cambrian deposits are preserved mainly in areas bordering the platform troughs, but they are eroded along its southern edge. They differ sharply from the underlying rocks and are composed of red sandstones and shales with limestone interlayers, in places of gypsum; on the area of ​​the troughs, they apparently also contain rock salt. The fauna is scarce and occurs rarely, mainly in limestones, less often in sandstones and clays (Lingula, Obolus, cap-shaped gastropods, algae).

The total thickness of the Cambrian rocks is about 1200-1500 m.

In other parts of the platform, the described section undergoes changes, sometimes quite significant. Along the southwestern edge of the platform, from the lake. Baikal to the Yenisei Ridge, Lower Cambrian deposits, apparently, completely pass into a red-colored sandy-clay member. In sandstones, sometimes quartz, sometimes arkose, of different grain sizes, diagonal layering and wave-cut signs are not uncommon; drying cracks occur in clays; fauna is completely absent. Rocks of this kind in the very marginal band of the platform make up the entire Lower Cambrian; along the river Irkut near the city of Usolye with the tops of the red-colored member is associated with a deposit of rock salt of industrial importance. As we move from the edge of the platform to its inner parts, limestones begin to appear in the section. Within the limits of the trough, the Cambrian deposits, apparently, are already approaching in composition the Lower Cambrian of the Lena section. The Middle Cambrian and Upper Cambrian deposits have no noticeable differences from the Lena deposits.

In the northwest of the platform, along the river. Dry Tunguska, in the core of a large anticline, the Cambrian emerges, composed exclusively of limestones with fauna conventional type. According to S. V. Obruchev, these limestones belong not only to the Middle, but also to the Upper Cambrian. Thus, in contrast to the southern areas of the platform, the Upper Cambrian in the northwest passes from a red sandy-clay facies into a purely carbonate marine one.

On the Anabar massif, along its southern margin (the Olenek River), the entire Cambrian section is composed of thick limestones with their usual organic remains (algae, trilobites, archaeocyates); approaching the central part (the outcrop of the Archean basement), the thickness of the section decreases, the limestones are gradually replaced by red-colored sandy-argillaceous rocks and, finally, near the outcrops of the Archean, they completely pass into them. Previously, these red-colored rocks were considered as belonging only to the Lower Cambrian, but according to Rozhkov and Moore, they compose the entire Cambrian section.

When considering - on the basis of the data presented - the Cambrian history of the Siberian Platform, it must be borne in mind, first of all, that wherever the contact of the Cambrian with the basement rocks was visible, it turned out that the Cambrian sediments lie unconformably on the sharply eroded surface of the Proterozoic and Archean. This means that at the very end of the Proterozoic Siberian platform, like Russian, was raised above sea level and was a continent. But already from the Lower Cambrian time, subsidence began and almost the entire length of the platform was flooded with sea. In the second half of Cm1, the distribution of facies shown in Fig. 1 was established on it. 49. A narrow zone of sandy-argillaceous red-colored rocks without fauna stretched along the southwestern edge of the platform, which was probably continental and partly lagoonal sediments (near Usolye - salts); The clastic material was apparently sourced from intrageosynclinal uplifts in the south. To the north, parallel to this strip, a second zone stretched in a wide ribbon - interbedded red-colored rocks and limestones with marine fauna, probably, the region of the upper part of the shelf, where a lot of clastic material was still delivered from the south. The central parts of the platform (regions of modern troughs) were occupied by purely carbonate facies, parts of which we now find in sections along the river. Lena and along the southern outskirts of the Anabar massif. On the Anabar massif itself, the deposits again passed to the north into a red-colored continental-lagoonal facies. Thus, already in the Lower Cambrian, the area of ​​the Siberian Platform was covered by a huge flat and in most cases very shallow sea with clear light water, in which numerous algae, archaeocyates, trilobites, brachiopods, gastropods lived, and algal and archeocyanate reefs often grew. Only in deeper places did limestone silts with a high content of organic matter accumulate; there were no algae and archaeocyaths here, but numerous trilobites and primitive brachiopods lived.

In the Middle Cambrian, there are characteristic shifts in sedimentation. Carbonate sediments, remaining the same type as before, occupy not only the middle part of the platform, but are distributed everywhere, excluding the extreme northeast - the Anabar massif, where red-colored facies are still preserved. This indicates that in the Middle Cambrian, the transgression that began in the Lower Cambrian continued and reached its maximum. Continental areas in its south, which existed in the Lower Cambrian, were flooded; the flow of detrital material was sharply reduced and calcareous oozes naturally became widespread.

The paleogeography of the Upper Cambrian (Fig. 50) differs markedly from that of the Middle Cambrian. In the vast expanses of the south and southeast of the platform, a mass of red-colored rocks is deposited, apparently due to the destruction of geosynclinal, at that time sharply uplifted, sections of the Sayan and Baikal region, adjoining the platform from the south.

Judging by the fauna and type of rocks, these red-colored Upper Cambrian sediments were partly deposited in the sea, partly on the surface of the continental areas that rose at that time among it - in their lakes, takyrs, lagoons. Only in the northeast, in the lower reaches of the river. Lena and along the river. Olenek, and in the north-west, along the river. Yenisei, the sea survived and the accumulation of carbonate sediments continued. All this indicates that during the Cm3 epoch, the Siberian platform experienced some uplift and related regression of the sea.

In general, during the Cambrian time, the Siberian platform made, as it were, one long and complex oscillatory movement - first downward, which caused the sea to transgress in the Lower and Middle Cambrian, and then upward, which entailed some regression of sea waters in the Upper Cambrian.

Tectorogeny throughout North Asia defines the Siberian platform, which occupies a vast territory between the Yenisei and Lena.

In the south, the platform extends to the latitude of the southern coast of Lake Baikal, in the southeast - to the Stanovoy Range and the coast of the Sea of ​​Okhotsk, in the north, the edge of the platform lies at the latitude of the mouth of the Khatanga.

Over the entire vast area, the Siberian Platform is covered by a thick sedimentary cover. Its crystalline foundation protrudes within the Anabar massif and the Aldan shield. The most important feature platform is its folded framing of successively located zones of the Baikal, Caledonian, Hercynian and Mesozoic folding.

By modern ideas(Tectonics of Eurasia, 1966), the crystalline basement of the Siberian Platform has a heterogeneous structure and consists of heterogeneous blocks formed in the pre-platform and platform periods (Bulina and Spizharsky, 1967). Older paleoblocks are preserved sections of folded systems that make up the base of the platform. The systems also include median massifs, structural-facies zones, anticlinoria and synclinoria, etc. With further subdivision of these structural elements into small parts, neoblocks were formed, which formed during the time from the Middle Proterozoic to the Early Triassic. Blocks of different nature are separated by faults. The regularities of the structure of the crystalline basement of this platform can, however, be interpreted in another historical and geological context. The main structural elements of the Siberian platform are the Anabar and Aldan Precambrian crystalline shields, as well as its Precambrian folded frame - the Stanovoy Range, the Eastern Sayan and the Yenisei Ridge.

The Siberian platform is one of the most clear examples successive build-up of the mainland earth's crust through the ocean. In the northeast of the mainland, folded formations fill the entire space between the platform and the Pacific Ocean, and are located between the Siberian platform and the crystalline massifs of Central and South Asia. A wide zone of Baikalids separates the Anabar and Aldan shields. The Angara-Lena trough, which extends in a northeasterly direction, is connected with it. On its continuation, the Vilyui syneclise is located and further - the Lena-Vilyui Mesozoic trough (Mikhailov and Filatov, 1967).

Precambrian deposits take part in the structure of the crystalline basement of the Siberian Platform. On the Anabar Shield, the most ancient Early Archean formations are represented by volcanogenic-magmatic rocks of basic composition (Tugarinov and Voitkevich, 1966). Late Archean formations are characterized by the predominance of biotite-amphibole gneisses and the appearance of carbonate rocks containing intrusions of alkaline granitoids and charnockites. The eroded surface of the Archean group of sediments is overlain by Proterozoic (Sinian) sandstones, gravelstones, limestones, and dolomites, whose age is 1500 million years.

Upper Archean deposits compose the Olenek crystalline massif, located 300 km east of Anabar. The age of the biotite granites exposed there, like those of the Anabar, is 2100 Ma (Tugarinov and Voitkevich, 1966).

The metamorphic strata of the Anabar Shield are collected in simple large folds extending into north westbound and complicated by secondary folding and faults.

Located in the southeastern part of the Siberian Platform, the Aldan shield extends in the north to the middle reaches of the Aldan, in the east to the upper reaches of the river. Uchur, in the south - to the Stanovoy Range and in the west - to the Olekma Valley. Further to the west, Precambrian structures are found in the Baikal Highlands and the Eastern Sayan Mountains. The southern and western folded margins of the shield, including the Stanovoi Ridge and the Olekma zone, are correlated with the Karelian folding (Tectonics of Eurasia, 1966). The central part of the Aldan shield is composed of metamorphic rocks subdivided into three series with a total thickness of 20,000 m. Their geochemical features are determined by the predominance of silica and alumina in the lower series, iron-magnesian silicates in the middle series, and carbonate compounds in the upper series. The entire Aldan section can be divided into two complexes: the lower one, associated with rocks of the basic composition, and the upper one, with a predominance of carbonate strata. The age of the rocks of the Aldan complex is 2800-1900 Ma (Tugarinov, Voitkevich, 1966).

The metamorphic strata of the Aldan massif form large simple folds extending in the northwestern, submeridional direction. According to A. A. Paturaev and I. Ya. Bogatykh (1967), these structures form a complex system of echelon-shaped folds, characterized by great complexity and the presence of subordinate folded structures of various orders. Numerous faults create a fold-block structure of the shield. Crushing zones and faults extend in the same direction as folding. There are a number of stages in their formation. The development of the platform basement ended in the Precambrian.

In the post-Cambrian time, the Siberian Platform was an arena of intense volcanism and sedimentation. In the Late Paleozoic and Early Mesozoic, significant subsidence in the southwest of the platform led to the formation of the Tunguska syneclise. Large structures are the Vilyui and Khatanga syneclises, the Irkutsk, Rybinsk, and Kansk-Yenisei troughs. The Angara-Lena trough, as noted, divides the Siberian platform into two independent parts. These troughs served as basins for the accumulation of platform cover, the formation of which began as early as the Late Proterozoic.

The thickness of the sedimentary cover on the Siberian platform is not the same. It is most significant within the Vilyuisky trough - about 3500 m, in the Tunguska syneclise - less and on the slopes of the platform is insignificant. The total thickness of sedimentary deposits is about 7000 m.

Sediments from the Cambrian to Quaternary systems take part in the structure of the sedimentary cover of the Siberian Platform, of which especially great importance in the structure of the relief they have Cambrian, Carboniferous, Permian and Triassic. The Cambrian system is composed of red sandy-argillaceous salt-bearing and carbonate rocks. Salt is being developed in a number of regions. In most cases, the Cambrian deposits lie quietly and form separate domes. In the Angara-Lena trough, the Cambrian and Silurian formations are collected into linear folds that make up the Prilensk fold zone.

Ordovician deposits are common on the margins of crystalline massifs and in the Angara-Lena trough. They are represented by shallow marine formations, which include a lot of limestone. Limestones are also found in the Silurian deposits. Devonian rocks fill the Rybinsk depression and lie on the outskirts of the Tunguska syneclise. The latter is characterized by carboniferous strata of the Carboniferous.

The Permian and Triassic deposits on the Siberian Platform include a thick volcanogenic sequence, in which traps are especially distinguished. They form dikes, veins, thick sheet-like deposits and covers in the north of the platform. Jurassic deposits are concentrated in the depressions of the Khatanga, Irkutsk, Kansk-Yenisei, Vilyui, and others. Tertiary deposits are widespread in the lower part of the Vilyui. Marine Quaternary formations of boreal transgression are known in the Khatanga and Lena depressions. During the maximum glaciation phase, the Siberian platform was covered continental ice. The features of the distribution of the sedimentary platform cover and its composition determine the main features of the relief of many regions of this country.

The Siberian platform is the main structural part of the tectonosphere, which determines the main features of the structure Northeast Asia. The crystalline foundation of the platform consists of separate parts different ages and structures connected at different times by sedimentary formations of predominantly geosynclinal origin.

Structures of different ages differ primarily in the composition and degree of metamorphism of their constituents. rocks. Structural-geomorphological analysis of the platform basement gives grounds to see a multi-island structure in its paleotectonics. There are two independent (Anabar and Aldan) centers of build-up of the Siberian Platform until the Late Proterozoic, which developed in parallel. In the era of Baikal folding, they were combined into one massif. The seam connecting the Anabar and Aldan shields runs in the direction of the Angara-Lena trough, filled with Cambrian, Silurian, and in the northeast and southwest - Jurassic deposits. A relic of the most ancient Angara-Lena geosyncline is, perhaps, the Baikal depression, pressed against the outskirts of the Aldan massif. Location in tectonically core can explain its long existence.

The Anabar massif is the oldest center of formation of the continental crust in North Asia. He occupied central location in the early Archean island system, stretching in a northeasterly direction. In addition to the Anabar shield, this system included, in separate links, the buried massifs of Igarka, Nizhneoleneksky, and Lyakhovsky, separated by troughs, subsequently filled with geosynclinal deposits. In the northwest, the Khatanga geosynclinal trough separated the paleotectonic system of the Anabar Islands from the Taimyr one, which formed later. The strike of Taimyr structures is generally northeast. The same strike can be traced on Bolshevik Island, which, according to structural and geomorphological features, apparently belongs to the island system of Novaya Zemlya. The latter is separated from the Taimyr system by a trough Kara Sea, which is a relic of the Paleozoic interisland basin.

The anticlinorium of Taimyr is composed of Precambrian metamorphological deposits, including numerous small Paleozoic intrusions (Tectonics of Eurasia, 1966). In Taimyr, rocks of the trap formation are known. Sandy-argillaceous, often flyschoid deposits take part in the structure of the trough. They are collected in steep linear folds. On the southeastern edge of the Khatanga trough, Jurassic and Cretaceous deposits are common, forming gentle cuestas. To the west, younger formations are developed. Calm landforms are associated with them.

The Taimyr fold country is a polystructural formation. It developed around individual massifs or islands of the outer (in relation to the Anabar shield) system from the Proterozoic to the Permian. According to the features of paleotectonics and geographical location, the structure is a marginal part of the Siberian platform, according to the time of formation, it is a Hercynian subplatform.

The Aldan Shield was a key part of the Precambrian complex island system stretching in a northeasterly direction from Baikal to Chukotka. The inner part of this system was the Aldan massif proper. With outside its island arc was located, which included the massifs of the Stanovoy Range and the Seimkan Mountains. A system of islands adjoined it, stretching in a northwesterly direction. Its main constituent parts were the Kolyma and Omolon massifs. To the north, in general, almost in the latitudinal southeast direction, the Chukchi paleotectonic island system of Northeast Asia stretched, passing to Alaska in North America. It includes the massifs Uelen, Wrangel Island, etc.

The Chukotka paleotectonic island system is a structural boundary between the basins of the Arctic and Pacific oceans, which emerged as early as the Precambrian.

The depressions between the paleotectonic island arcs of Northeast Asia served for a long time as basins for the accumulation of geosynclinal deposits. The latter are dominated by volcanogenic formations. Dislocated sedimentary strata determine the modern geomorphological appearance of this country.

The tectonic relief of the Siberian Platform has a long history of development. Structural, accumulative and denudation forms naturally combine here. All these complexes are determined to some extent by the lithological composition of relief-forming rocks. The surface of the platform is characterized by the Central Siberian in the north and the Aldan plateau in the south. They correspond to the Anabar and Aldan shields. The plateau delimits the Leno-Vilyui alluvial lowland, which occupies a trough and adjacent parts of the shields.

In the northwest, the Anabar shield is adjacent to the North Siberian accumulative lowland, located within the Khatanga trough. Further to the west rises the Taimyr Highlands. The Byrranga mountains stand out in its relief. Their structure is dominated by sandstones and traps, the massifs and rocks of which give the relief of the mountains a uniform severity.

The structural topography of the southern part of the Siberian Platform is much more complex. Throughout its length from the Sea of ​​Okhotsk to Lake Baikal, it is bordered by mountain ranges and highlands. They are characterized by a folded-block structure. General feature their topography - the ancient leveling surface - is also the top surface. Located at different heights, it serves as an indicator of the amplitude of movements that occurred after its formation. The magnitude of vertical displacements of blocks in many cases is measured in thousands of meters.

The mountainous structures of the southern part of the platform are separated by significant intermountain depressions made by younger sediments compared to the rocks that form the ridges. Their relief is flat, accumulative. In some places, it becomes more complicated depending on the lithological composition of the rocks.

The ancient structural relief of the considered part of the Siberian Platform is the relief of the Stanovoi Range, the Patom Upland, the Vitim Plateau, the Eastern Sayan Mountains, Eastern Tuva, etc. The Stanovoi Range extends eastward from the middle reaches of the Olekma for 700 km. Further, its continuation is the Dzhugdzhur ridge. In the orography of the Stanovoy Range, two or three parallel ridges are distinguished, elongated in the direction of the strike of the ridge. Its structure is dominated by gneisses and shales of the Precambrian age, containing intrusions of various igneous rocks. In some places, strata of sedimentary rocks of the Cambrian and Jurassic systems occur.

The relief of the Stanovoy Ridge is characterized by wide rounded ridges and individual dome-shaped mountain peaks. In the most high parts The mountains are dominated by rocky bald mountains and stone placers. Their foothills are covered with talus and covered with deluvial-proluvial covers. The upper reaches of the rivers here have wide and flat valleys. Down the slope, the valleys deepen and become narrow. Glacigenic landforms are common in the western part of the range. Such common features relief are also characteristic of the Baikal mountainous country.

The Siberian platform is bounded by deep fault zones - marginal sutures, well-defined gravity steps, and has a polygonal outline. Modern borders platforms took shape in the Mesozoic and Cenozoic and are well expressed in the relief. Western border the platform coincides with the valley of the Yenisei River, the northern platform coincides with the southern margin of the Byrranga Mountains, the eastern platform coincides with the lower reaches of the Lena River (Verkhoyansky marginal foredeep), in the southeast with the southern tip of the Dzhugdzhur ridge; in the south, the boundary runs along the faults along the southern margin of the Stanovoy and Yablonovy ridges; then, going around from the north along a complex system of faults in Transbaikalia and the Baikal region, it descends to the southern tip of Lake Baikal; the southwestern boundary of the platform extends along the Main East Sayan Fault.

On the platform stands out mainly the foundation and the platform cover (-). Among the main structural elements of the platform stand out: Aldan shield and Leno-Yenisei plate, within which the foundation is exposed on the Anabar massif, Olenyok and Sharyzhalgay uplifts. West Side the plates are occupied by the Tungusskaya, and the eastern one by the Vilyui syneclise. In the south there is the Angara-Lena trough, separated from the Nyu depression by the Peledui uplift.

The foundation of the platform is sharply dissected and composed of highly metamorphosed Archean rocks, which have latitudinal strikes in the western half and north-northwest strikes in the eastern half. Weaker metamorphosed strata of the Lower Proterozoic (Udokan series) are preserved in separate depressions and grabens, lie gently and are formations of the protoplatform cover.

A typical platform cover begins to form from the Riphean time and 7 complexes are distinguished in its composition. The Riphean complex is represented by carbonate-terrigenous, red-variegated rocks 4000-5000 m thick, filling aulacogenes and gentle depressions. The Vendian-Cambrian complex is composed of shallow-water terrigenous and terrigenous-carbonate deposits, and in the Angara-Lena trough - and saline (lower - middle Cambrian) strata, 3000 m. The Ordovician-Silurian complex is represented by variegated terrigenous rocks, as well as limestones and dolomites, 1000- 1500 m. The Devonian-Lower Carboniferous complex is limited; in the south, the Devonian is represented by continental red-colored strata with traps, in the north - by variegated carbonate-terrigenous deposits; in the Vilyui syneclise - a thick trap stratum and salt-bearing deposits, 5000-6000 m. - tuff and upper - lava parts (undifferentiated tholeiitic basalts); all deposits are intruded by dikes, stocks and sills of basalts; in the Devonian, Triassic and Cretaceous, kimberlite explosion pipes form in the northeast of the platform. The Upper Triassic-Cretaceous complex is composed of continental and less often marine sandy-clayey coal-bearing deposits, 4500 m, distributed only on the outskirts of the platform. The Cenozoic complex is developed locally and is represented by continental deposits, weathering crusts, and glacial formations. The Paleogene Popigai astrobleme is known in the Anabar massif.

The Siberian platform is characterized by intense magmatism, manifested in the early Proterozoic, Riphean - early Cambrian, Middle, Upper Paleozoic - Triassic and late. Trap magmatism absolutely dominates in volume (more than 1 million km3).

The Siberian platform is rich

The Siberian Platform occupies a central place in the structure of North Asia and is located in the interfluve largest rivers Eastern Siberia - Yenisei and Lena. In plan, the Siberian platform has the shape of an irregular polygon, somewhat widening to the south. The southeastern boundary of the Siberian platform coincides with the Mongol-Okhotsk suture, which separates the Early Precambrian crystalline complexes of the Stanovoy block from the folded structures of the Mongol-Okhotsk belt formed at the end of the Triassic - Jurassic. To the west, the fields of development of the Early Precambrian formations of the Stanovoi block are “lost” in the sea of ​​Early Paleozoic granitoid batholiths and volcanic rocks of the Baikal folded region. Here, the boundary of the platform is drawn largely conventionally along a submeridional line continuing to the south of the Zhuinsky Fault. Within the Northern Baikal region, the distribution boundary of the Siberian Craton marginal complexes is located within the well-defined North Baikal or Patom arc. This territory in the Riphean, Vendian, and Early Paleozoic was a passive margin of the Siberian continent, which was deformed as a result of accretionary-collisional events in southern Siberia. The southwestern margin of the craton is formed by the structures of the Sayano-Yenisei fold-cover region. The entire western periphery of the Siberian Platform is covered by the Meso-Cenozoic sedimentary cover of the West Siberian Plate. Here the border of the platform is rather conventionally drawn along the valley of the Yenisei River. In the north, the platform complexes of the Siberian craton are buried under the sediments of the Yenisei-Khatanga trough, an offshoot of the West Siberian epipaleozoic basin, and are bounded by the structures of the Taimyr-Severozemelskaya fold-cover region. The eastern periphery of the Siberian Craton is formed by the deformed Verkhoyansk complexes. Here, predominantly sedimentary complexes formed on the outskirts of the Siberian continent during the Paleozoic and Mesozoic are torn off the crystalline base and thrust towards the platform. The Pre-Verkhoyansk foredeep was formed in the thrust front.

The basement of the craton protrudes to the surface in the southeast, within the Aldan-Stanovoi shield. Two main tectonic elements are distinguished in its structure - the Aldan megablock itself, which occupies the northern part of the shield, and the Stanovoy megablock located to the south.

The Aldan block is divided by submeridional faults into three tectonic elements. Western Chara-Olekminsky and eastern Batomgsky represent a typical granite-greenstone region, and the Central Aldan (Aldan-Uchursky) located between them is a representative of granulite-gneiss regions.

Within the Central Aldan block, plutonic rocks of tonalite-trondhjemite composition are widespread. The subordinate value belongs to two supracrustal strata. The first is composed of high-alumina shales and quartzites, i.e., metamorphosed "mature" sedimentary rocks, products of the redeposition of ancient weathering crusts. For the second, basic crystalline schists, metagraywackes, metapelites, carbonates, and ferruginous quartzites are typical. The primary rocks were mafic volcanics and silty-argillaceous sediments with carbonate interbeds. The rocks underwent at least two epochs of regional amphibilite and granulite metamorphism in the late Archean and early Proterozoic. The development fields of these complexes are characterized by large granite-gneiss domes with a diameter of many tens of kilometers. They form oval and irregular in terms of complex folded forms, in the cores of which granites and migmatites are exposed. According to the available isotopic datings, the formation of the continental crust of these regions occurred in the interval of 3.5–3.8 and 3.5–3.0 Ga.

The structure of the granite-greenstone regions of the Aldan megablock (Chara-Olekminsky and Batomga blocks) is very diverse. The composition of the greenstone belts extending in the meridional direction is dominated by volcanic rocks of basic, less often medium and felsic compositions, metamorphosed under conditions of greenschist and amphibolite facies, as well as metasedimentary rocks - gravuacca, pelites, carbonates and ferruginous quartzites. The formation of the rocks of this complex is associated with evolution ocean basins separating the granulite-gneiss blocks of the base. The latter are composed of Middle Archean (3.2–3.0 Ga) diorite-tonalites, monzodiorites, granulites, crystalline schists, and gneisses. As a result of the convergence of continental blocks and the closure of oceanic basins at the collisional stage of 1.9–2.0 Ga (i.e., during the Svecofennian tectonomagmatic epoch), narrow rectilinear troughs with all signs of structural seams were formed. Widely manifested granitoid magmatism corresponds to the same stage.

The Stanovoy megablock, located in the southern part of the Aldan-Stanovoy shield, has a special structure. Along with the Archean rocks metamorphosed, as in the Aldan megablock, in the granulite facies, gneiss and granite-gneiss formations of the amphibolite-granulite facies of metamorphism are widespread. However, the main distinctive feature The structure of the Stanovoy block is a multiple tectonomagmatic reworking, which continued here until the Cenozoic. These processes are most intense at the Late Jurassic - Early Cretaceous stage and are caused by subduction processes from the side of the Mongol-Okhotsk mobile belt.

The Proterozoic complexes of the Aldan-Stanovoi shield include the strata of the Udokan series, which fill the trough of the same name in the southwest of the Chara-Olekma zone. As the main reason for the initiation of this depression, rifting at the turn of 2.2 billion years is assumed. It is performed by a very thick (up to 12 km) sequence of continental detrital reds. Bottom part This sequence is metamorphosed in greenschist and partly amphibolite facies and deformed by granite-gneiss domes that arose due to the remobilization of the Archean substrate. Time of metamorphism 1.85-1.9 million years. Approximately the same moment corresponds to the intrusion of granites (Kodar massif).

Volcanic belts also belong to the Proterozoic complexes of the platform: Akitkansky, traced in the Primorsky Range along west coast lake Baikal, and Ulkansky, located on the eastern outskirts of the Aldan megablock. Both belts were formed at the turn of 1700-1800 million years ago. The Akitkan belt is the standard of the Proterozoic calc-alkaline volcanic belts. It is composed of andesites, trachytes, trachyandesites, ignimbrites, porphyrites, and numerous tuffaceous formations, which are associated with coarse detrital volcanic-detrital molassoid strata, which makes it possible to compare it with volcanoplutonic belts of active continental margins. The Akitkan belt fixes the outskirts of the Angara-Anabar block. The presence of the belt shows that even at the boundary between the Early Proterozoic and the Riphean, this block was separated from the Aldan block.

The second major outcrop of the basement on the Siberian platform is the Anabar shield located in the north. Its structure includes Archean granulite-gneiss areas (Magan and Daldyn terranes), Early Proterozoic complexes of continental margins (Khapchan terrane), and collision zones (Magan, Kotuykan, Billyakh).

The Magan tonalite-trondjemitic-gneiss terrane stands out in the western part of the shield. It is composed of biotite, biotite-amphibole orthogneisses, interlayers of metacarbonates and quartzites are present.

The Daldyn enderbite-gneiss terrane occupies the central part of the shield. It is bounded from the west by the Kotuykanskaya and from the east by the Bilyakhskaya melange zones and is dissected almost in the middle by the Main Anabar Fault of shear kinematics. The terrane is composed mainly of primary enderbites and mafic schists, in lesser degree metasedimentary rocks are developed: quartzites, carbonate deposits. The age of the protolith of the rocks of the Daldyn terrane is estimated at 3.1 Ga. Granulitic metamorphism and deformations synchronous to it embraced the substrate rocks of both terranes at the level of 2.8 Ga and was accompanied by the formation of charnockite-enderbite areas.

The Khapchan terrane located in the east is composed mainly of Early Proterozoic metamorphosed sedimentary rocks: limestones, dolomites, greywackes and marls. Such rock associations point to the shallow-water, shelf environments of the Early Proterozoic passvin continental margin. The metamorphism of the Khapcha Series reaches the granulite facies. The age of metamorphism is estimated at 2.0–1.9 Ga, and the model age of the protolith is no older than 2.4 Ga. Archean enderbites and schists of the base of the terrane, similar to those of the Daldyn block, are exposed very fragmentarily.

The structure of the Kotuykan and Billyakh collision zones, which cross-link the described granulite-gneiss terranes, is represented by a series of subparallel faults of shear-thrust kinematics. Within these zones, blocks of granulites and anorthosites occur in the form of large tectonic outliers, accompanied by pyroxenites with an age of 2.1 Ga. The host matrix is ​​a variety of cataclasites, blastomylonites of the amphibolite facies and accompanying migmatites and autochthonous granites with an age of 1.85–1.9 Ga.

The Khapchan complex described above is also distributed to the east of the Anabar shield and again emerges on the surface at the top of the Olenek arch. According to geophysical data, the Magansko-Daldynsky complex extends under the cover of the platform to the west up to the meridional Sayan-Taimyr fault, which cuts through the entire Siberian craton up to Lake Baikal. To the west of this fault, the Tunguska megablock stands out in the basement, the rocks of which are exposed along the southwestern, Sayan periphery of the craton. In fact, they are involved in newest structure of the East Sayan orogen (see the chapter "Sayan-Yenisei fold-cover region"), but primarily belonged to the basement of the craton. General structure the foundation of the Siberian Platform is shown in Fig.

The formation of the sedimentary cover on the Siberian platform, as well as on the East European platform, was preceded by a stage of intracontinental rifting. Riphean aulacogens form a rather complex network in the body of the Siberian craton. They wedge out towards the center of the craton and, on the contrary, open towards the peripheral mobile belts. The systems of Riphean graben-like depressions in the north of the platform of submeridian strike are most pronounced: Udzhinsky, Maimechinsky (Kotuisky), Turukhan-Norilsk aulacogenes. The formation of the Vilyui-Patom graben system belongs to the Devonian period. elongated in a northeasterly direction at the base of the Vilyui syneclise.

The main tectonic structures of the platform cover are clearly visible on the relief map of the surface of the crystalline basement (Fig.). As part of the plate complex, it is customary to distinguish several structural stages corresponding to independent large tectonic stages of its formation: Riphean, Vendian-Lower Paleozoic, Middle-Late Paleozoic, Mesozoic-Cenozoic. Each of them is characterized by its own structural plan, features of the composition of the constituent sedimentary and igneous complexes.

structural plan The Riphean stage of the plate complex is characterized by the presence of extensive flat troughs and uplifts, against which there were deeper narrow graben-like depressions and, thus, is confined to aulacogenes. They are especially numerous in the northeast of the platform and are filled with a characteristic graben facies with local manifestations of alkaline volcanism, which is gradually replaced upsection by shallow-marine sandy-argillaceous and carbonate sediments. A feature of the Riphean stage in the development of the plate complex of the Siberian Platform, in comparison with the East European one, is that sedimentation was not limited to rift troughs, but extended beyond it. The Aldan shield remained steadily uplifted throughout the entire Riphean. Riphean rocks come to the surface on the eastern slope of the Adana shield, the Anabar massif and the Olenek uplift within the Turukhano-Igarsk dislocation zone.

At the end of the Riphean-Vendian, the peripheral zones of the craton turned into passive continental margins of the newly formed ocean basins. The structural plan of the Vendian-Lower Paleozoic complex and the redistribution of sedimentation areas are inextricably linked with tectonic events on the margins of the continent, i.e. with the formation of movable belts framing the platform. The first signs of restructuring, violations of the integrity of the southern (in modern coordinates) margin of the platform belong to the Vendian. They led to the appearance of land barriers in the Yenisei Ridge and the Western Baikal region and were expressed in angular unconformities at the base of the Vendian. The Vendian-Cambrian time is characterized by a general subsidence of the platform and, accordingly, a wide transgression of the sea. The uplift grew only in the place of the Eastern Sayan. It was associated with the formation of the Caledonian front of the folds of southern Siberia. The remaining outskirts of Siberia continued to experience a calm subsidence. At the base of the section, there are basal conglomerates, gravelstones, sandstones gradually giving way to shallow marine and lagoonal terrigenous-carbonate and gypsum-dolomitic sediments. Ordovician deposits conformably overlie the Cambrian, but are less widespread - the platform submerged mainly in the western Olekma-Tunguska part of the platform. Since the late Ordovician and into the Silurian, ascending movements have predominated. The gradual uplift of the southeastern part of the plate during the Ordovician and Silurian became the prototype for the formation of the future Tunguska syneclise. The deposits of this period of time are characterized by a combination of shallow-water carbonate (limestone, dolomite, marl), to a lesser extent - terrigenous (argillite, graptolitic shales, less often siltstone), as well as sulfate rocks. The gradual regression of the sea and the drying of the central and southeastern parts of the platform by the beginning of the Devonian is due to the collision and subsequent deformations within the Baikal folded region.

A new stage in the development of the Siberian Platform plate complex began in the Devonian and is associated with a new episode of continental rifting and the formation of the Vilyui aulacogen system on the eastern margin of the platform. As a result of these processes, a huge sedimentary basin was laid in the Verkhoyansk region, the subsidence of which continued at the Mesozoic stage of the history of the development of the plate. As a result, an extensive Vilyui syneclise took shape in the east of the platform.

As an independent structural complex of the East Siberian Plate, Carboniferous, Permian and Triassic deposits of the Tunguska syneclise are distinguished. The formation of the basin at the site of the Tunguska syneclise is associated with stretching and thinning of the continental crust over a vast hot spot mantle. The base of the depression section is represented by terrigenous rocks of the Tunguska series, saturated with layers hard coal. Up the section - towards the Late Permian - the coal-bearing series is replaced by tuffaceous deposits and further by a powerful trap formation of the Late Permian - Early Triassic, formed as a result of the functioning of the largest plume.

Among other manifestations of within-plate magmatism on the territory of the Siberian Platform, Riphean alkaline-ultrabasic massifs are known in the region of the Udzha aulacogen, as well as within the Aldan shield. Explosion pipes and dikes made by diamond-bearing kimberlites are widely represented. The intrusion of kimberlite bodies occurred in three main epochs: at the end of the Devonian, in the Triassic and in the Cretaceous, and are confined to strictly defined areas, the main of which are the Tunguska-Vilyui saddle, the marginal part of the Olenek uplift, the southeastern slope of the Anabar massif.

The formation of the Mesozoic-Cenozoic structural stage of the plate is associated with Triassic rifting, in Western Siberia and the Yenisei-Khatanga trough, which resulted in the lowering of the adjacent edges of the platform. In general, at the end of the Mesozoic, due to the formation of folded fronts of the Verkhoyansk zone and Taimyr, a gradual drying of most of the platform occurred, and during the Cenozoic, the platform was mainly a denudation area.

SIBERIAN PLATFORM - one of the large, relatively stable areas of the continental crust, belonging to the number of ancient (pre-Riphean) platforms, occupies the middle part of North Asia. Siberian platform is limitedzones of deep faults - marginal seams, well-defined gravitational steps, and has a polygonal outline. The modern boundaries of the platform took shape in the Mesozoic and Cenozoic and are well expressed in the relief. The western boundary of the platform coincides with the valley of the Yenisei River, the northern one - with the southern margin of the Byrranga mountains, the eastern one - with the lower reaches of the Lena River (Verkhoyansk marginal trough), in the southeast - with the southern tip of the Dzhugdzhur ridge; in the south, the boundary runs along the faults along the southern margin of the Stanovoy and Yablonovy ridges; then, going around from the north along a complex system of faults in Transbaikalia and the Baikal region, it descends to the southern tip of Lake Baikal; the southwestern boundary of the platform extends along the Main East Sayan Fault.

On the platform, the Early Precambrian, mainly Archean, basement and platform cover (Riphean-Anthropogenic) stand out. Among the main structural elements of the platform stand out: the Aldan Shield and the Leno-Yenisei Plate, within which the foundation is exposed on the Anabar massif, Olenyok and Sharyzhalgai uplifts. The western part of the plate is occupied by the Tungusskaya, and the eastern part by the Vilyui syneclise. In the south there is the Angara-Lena trough, separated from the Nyu depression by the Peledui uplift.

The foundation of the platform is sharply dissected and composed of highly metamorphosed Archean rocks, which have latitudinal strikes in the western half and north-northwest strikes in the eastern half. The weaker metamorphosed strata of the Lower Proterozoic (Udokan Group) are preserved in separate depressions and grabens, lie gently and are formations of the protoplatform cover.

A typical platform cover begins to form from the Riphean time and 7 complexes are distinguished in its composition. The Riphean complex is represented by carbonate-terrigenous, red-variegated rocks 4000-5000 m thick, filling aulacogenes and gentle depressions. The Vendian-Cambrian complex is composed of shallow-water terrigenous and terrigenous-carbonate deposits, and in the Angara-Lena trough - and salt-bearing (lower - middle Cambrian) strata, 3000 m. m. The Devonian-Lower Carboniferous complex is limited; in the south, the Devonian is represented by continental red-colored strata with traps, in the north - by variegated carbonate-terrigenous deposits; in the Vilyui syneclise - a thick trap stratum and salt-bearing deposits, 5000-6000 m. - tuff and upper - lava parts (undifferentiated tholeiitic basalts); all deposits are intruded by dikes, stocks, and basalt sills; in the Devonian, Triassic and Cretaceous, kimberlite explosion pipes are formed in the northeast of the platform. The Upper Triassic - Cretaceous complex is composed of continental and less often marine sandy-clayey coal-bearing deposits, 4500 m, distributed only on the outskirts of the platform. The Cenozoic complex is developed locally and is represented by continental deposits, weathering crusts, and glacial formations. The Paleogene Popigai astrobleme is known in the Anabar massif.

The Siberian Platform is characterized by intense magmatism, which manifested itself in the Early Proterozoic, Riphean - Early Cambrian, Middle Paleozoic, Upper Paleozoic - Triassic and Late Mesozoic. Trap magmatism absolutely dominates in volume (more than 1 million km3).

The Siberian platform is rich in minerals. Large deposits of iron ore are located on the Aldan shield, in the Angara-Ilim iron ore basin. Copper-nickel sulfide deposits are associated with traps in the Norilsk ore region, and cuprous sandstones are developed in the Udokan series on the Aldan Shield. Diamonds are timed to kimberlite pipes. Large deposits of coal are known on the Siberian platform (the Lena coal basin, the Tunguska coal basin, the Irkutsk coal basin, the Kansko-Achinsk coal basin, the South Yakutsk coal basin), deposits of rock and potassium salt, gypsum, phosphorites, manganese and gold ores, graphite, mica ( phlogopite), fluorite and other minerals. Mountain Encyclopedia

Geological history

1. In the Archean and the beginning of the Proterozoic, most of the basement of the East Siberian Platform was formed.
2. At the end of the Proterozoic (Vend) and the beginning of the Paleozoic, the platform was periodically covered by a shallow sea, resulting in the formation of a thick sedimentary cover.
3. At the end of the Paleozoic, the Ural Ocean closed, the crust of the West Siberian Plain consolidated, and it, together with the East Siberian and East European platforms, formed a single continent.
4. In the Devonian, an outbreak of kimberlite magmatism.
5. On the border of the Permian and Triassic occurred powerful flash trap magmatism.
6. In the Mesozoic, some parts of the platform were covered by epicontinental seas.
7. At the boundary of the Cretaceous and Paleogene, rifting and a new outbreak of magmatism, including carbonatite and kimberlite, took place on the platform. Russian Wikipedia

To the essence of the concept

The concept of "Siberian platform" was first introduced into the geological literature by A. A. Borisyak in 1923. Since then, the Siberian platform has been understood as a vast region of Eastern Siberia with a two-story tectonic structure. This is a segment of the earth's crust, relatively stable from the Riphean to the Cenozoic, limited by folded structures of the Late Proterozoic, Paleozoic and Mesozoic age. The lower structural stage - the basement is composed of Early Precambrian predominantly crystalline rocks, the upper (sheath) - non-metamorphosed relatively weakly dislocated sedimentary and volcanogenic-sedimentary strata with age from Riphean to Cenozoic. The area of ​​the Siberian platform in the modern erosion section is over 4 million square kilometers.

Hydrography

The Siberian platform is located between the Yenisei in the west and the Lena with a tributary of the Aldan in the east. These mighty rivers flow in a submeridional direction and flow into the marginal seas of the Arctic Ocean. The Yenisei flows into the Kara Sea, the Lena into the Laptev Sea. Their tributaries cross the territory of the Siberian Platform mainly in the sublatitudinal direction. The main tributaries of the Yenisei (from south to north): Angara or Upper Tunguska, Podkamennaya Tunguska, Lower Tunguska and Kureika. All of them are right tributaries of the Yenisei. The main right tributaries of the Lena River (from south to north): Kirenga, Vitim, Olekma and Aldan; left tributaries (from south to north): Kuta, Vilyui. In the north of the platform, in addition, the Olenyok, Anabar and Khatanga rivers flow into the Laptev Sea (from east to west).

Orography

The relief of the platform is very diverse. Most its territory is occupied by the Central Siberian Plateau. Against the background of the general high standing of the surface of the platform, separate more elevated areas stand out, which are called plateaus. In its northwest there is the Putoransky (Putorana Plateau), in the northeast - the Anabarsky, in the west - the Tungussky and Zaangarsky, in the southwest - the Angarasky, in the south - the Leno-Angarasky and Prilensky plateau. From the south, the platform is surrounded by mountain structures, the uplift of which also involves its marginal parts (from east to west): the Al-Dano-Stanovoe and Baikal-Patom highlands, the mountains of the Western Baikal region and the Eastern Sayan, the uplift of the Yenisei Ridge. From the north, the Central Siberian Plateau is surrounded by lowlands: West Siberian in the west and northwest, North Siberian in the north and Central Yakut in the northeast. The last two occupy part of the territory of the Siberian Platform. To the east of the Central Yakutsk lowland lies the Verkhoyansky Range, to the north of the North Siberian Lowland there is the sea, and on the Taimyr Peninsula there is the Byrranga Range. Buldygerov, p.5

Sources

1. Buldygerov V.V. Geological structure Irkutsk region. Irkutsk. 2007
2. Mountain Encyclopedia. In 5 vols. M. "Soviet encyclopedia. 1984-1991
3. Russian Wikipedia