The Ural Mountains are located between various tectonic structures. Physical Geography - Ural (Ural Mountains)

The geological map of the Urals clearly shows the zonality of its structures. Rocks of different ages, compositions and origins stretch meridionally over a vast stretch. From west to east, six successive bands are distinguished, with the western bands being traced along the entire length of the ridge, the eastern bands are observed only in the middle and southern regions of the Eastern Slope, since in the northern regions the Paleozoic rocks are overlain by the Mesozoic, Paleogene and Neogene sediments of the West Siberian lowland.

Normally sedimentary Permian, Carboniferous and Devonian deposits are involved in the formation of the first band, traceable throughout the Urals and evenly replacing each other from west to east. A part of the Western Slope at the latitude of the Ufa Plateau stands out very sharply in terms of the nature of the location of the rocks. Here, the entire stratum of Carboniferous deposits, and in some places even Devonian ones, often falls out of the section, partially or completely; in such cases, the Permian rocks are brought into direct contact now with the Lower Carboniferous, now with the Devonian, now with the Silurian deposits.

The second band morphologically constitutes the axial part of the ridge and is composed of quartzites, crystalline schists, and generally strongly metamorphosed Lower Paleozoic and Precambrian formations. Against the Ufimskoe plateau, the rocks of the second band are wedged out over a rather considerable extent.

The third band already belongs to the Eastern Slope and consists entirely of altered volcanogenic accumulations, in which large bodies of gabbro-pyroxenite-dunite intrusions are embedded. They lie along the eastern boundary of the crystalline schists of the second band in the Northern and Middle Urals; in the Southern Urals there are numerous, but small massifs of serpentines, sometimes with peridotites preserved among them. Petrographically, however, these formations are not identical to gabbro-peridotite-dunite intrusions. The Quaternary band lies within effusive rocks and tuffs of predominantly mafic magma from the Silurian to the Lower Carboniferous inclusive. Among them, sedimentary marine accumulations occur in a sharply subordinate amount. All these formations are strongly dislocated and turned into shales and greenstone strata.

The fifth band is represented by granite-gneiss massifs of the Upper Paleozoic intrusions, in the eastern parts covered by Tertiary deposits.

The sixth band is composed of highly metamorphosed, dislocated Middle and Upper Paleozoic formations, volcanogenic in the lower part, normally sedimentary in the upper part. They are cut through by intrusive rocks of various compositions. Exposures along the Eastern Slope of the Southern Urals show that the rocks of the sixth band are gradually submerged in the direction from west to east into the region of the present-day West Siberian Lowland.

Large overthrusts are developed along the boundaries of the bands.

A.D. Arkhangelsky at one time concluded that the first band is a monocline; the second, third and fifth bands structurally represent huge anticlinoria; the fourth and, possibly, the sixth have the form of large synclinal troughs.

At present, such a tectonic structure of the Urals is proposed. To the east of the Cis-Ural marginal foredeep follow: the Bashkir anticlinorium, the Zilair synclinorium, the Central Ural anticlinorium, the Magnitogorsk synclinorium and the Nizhny Tagil synclinorium continuing it to the north, the anticline zone of granite intrusions, the East Ural synclinorium, and the Transural anticlinorium. To the east, the folded structures of the Urals submerge under the Mesozoic and Cenozoic deposits of the West Siberian Lowland.

The general strike of the structures of the Urals is meridional or close to it. The Bashkir anticlinorium is composed of Lower Paleozoic rocks; Silurian and Lower Devonian are absent. Despite the high age of the rocks, they are characterized by weak metamorphism. The strike of the folds in the southern parts is almost meridional, in the northern parts it deviates to the east. Here, the direction of the folds depends on the configuration of the eastern edge of the Russian Platform.

Between the Bashkir and Central Ural anticlinories lies the Zilair synclinorium. In the south of the Western Urals, it bypasses the Bashkir anticlinorium and becomes the western margin of the Urals there. Similarly, in the north about 51 ° N. sh. the Zilair synclinorium closes, and there the Central Ural anticlinorium becomes the marginal zone of the Urals. The Zilair synclinorium is composed of rocks from the Lower Paleozoic to the Tournaisian, inclusive. One can clearly see the difference in stresses and eroded folding of the lower complex and the calm upper one, starting from the Upper Devonian deposits.

A sharp tectonic difference between the Western and Eastern Urals was outlined by F.N. Chernyshev and A.P. Karpinsky.

The type of cover structures actually exists, probably, only at the latitude of the Ufimsky plateau. Geological study of the Urals, carried out by E. A. Kuznetsov, in the transverse direction along a well-exposed area along the river. Chusovoi, from the west of Kuzino station to Bilimbay, revealed here the phenomena of large thrust structures.

Throughout the Urals, a huge structure can be traced - the Central Urals anticlinorium, which from the Middle Urals to the Polar inclusive is a marginal folded zone. The anticlinorium is composed of sedimentary, igneous, and metamorphic Precambrian and Lower Paleozoic rocks. In the western part, younger strata up to the Permian unconformably lie on their eroded intense folds.

The Magnitogorsk and Nizhny Tagil synclinorium already belong to the Eastern slope of the Urals and they were built mainly by Middle Paleozoic, especially volcanogenic accumulations, which underwent greenstone regeneration due to their dislocation. Three volcanic cycles have been established: 1) Silurian-Lower Devonian; 2) Middle Devonian - Upper Devonian; 3) Lower Carboniferous.

To the east, only in the southern part of the Urals is the anticline zone of granite intrusions (from 59° N and ending with Mugodzharami). This is a zone of huge granitoid massifs, such as the Saldinsky, Murzinsky, Verkh-Isetsky, Chelyabinsky, Troitsky, Dzhebyk-Karagaysky. Basic and ultrabasic rocks here are of sharply subordinate importance. It is now believed that highly dislocated Lower Paleozoic and Pre-Paleozoic rocks are widespread within this structure.

To the north from 58° to 51° N. sh. there is the East Ural synclinorium with predominant Middle Paleozoic formations in the presence of Middle Carboniferous, possibly younger, and Upper Triassic coal-bearing accumulations of the Chelyabinsk type. The folds are overturned to the east. Many intrusive deposits. The Trans-Ural anticlinorium in the Southern Urals is a marginal eastern structure formed by ancient rocks. The relationship between the northern parts of the Urals and the folded regions of Pai-Khoi and Vaigach-Novaya Zemlya has not yet been clarified. They indicate that north of Konstantinov's Stone along the western shore of Lake. The Bolshoi Osovei thrust extends almost to the coast of the Kara Sea. Spilites and diabases lying along it at the base of the Silurian are in contact with the rocks of the Upper Paleozoic Pai-Khoi. There is evidence of a close structural and facies relationship between Pai-Khoi and Vaigach, Novaya Zemlya and the Pechora basin. It is also believed that the northern part of the Taimyr Peninsula and about. Northern Land. The geological profile along the Bisert - Bogdanovich line at the latitude of the Ufimsky plateau can well show the significance of the latter in the formation of the structures of the Urals. Here, the strata of both slopes are strongly reduced. The western band is characterized by scaly folding with sharp overthrusts, especially between the Paleozoic and the metamorphic suite. The northwestern strike-slip narrowed the greenstone band to negligibly small sizes. As in the previous profile, a large Upper Iset massif is located between the greenstone strip and Sverdlovsk. The main rocks were the first to intrude here; they were followed by plagiogranites and granites of normal composition.

To characterize the tectonics of the Southern Urals, we will use the data of A. A. Bogdanov. On the Western slope, he distinguishes the following main structural elements: the Ural-Tau and Bashkir anticlinorium, separated by the Zilair synclinorium, the southern part of which is complicated by the Sakmara anticlinorium; zone of block faults framing the Bashkir anticlinorium; a number of linear folds of the Orenburg-Aktobe Cis-Urals located on the Sakmara flexure; a zone of complex folded structures of the Eastern Slope of the Urals, adjacent from the east to the Ural-Tau anticlinorium.

The schematized sections constructed by A. A. Bogdanov clearly show two structural tiers. The lower one consists of complex folded pre-Devonian strata and represents geosynclinal Caledonides; the upper one is built by Devonian, Carboniferous, and Permian rocks, unconformably overlying the Caledonides; here the rocks are collected in calm gentle folds, and in the west, in the region of the Russian platform, they take on a horizontal bedding. A similar two-tiered structure can be traced along the entire Western slope of the Urals, representing, therefore, a Caledonian structure, unconformably overlain by Hercynian structures of a postgeosynclinal nature.

The eastern slope along its entire length is a typical eugeosynclinal structure of the Hercynian tectogenesis, broken by normal faults into horsts and grabens. In the latter, Mesozoic and Cenozoic continental accumulations lie on the eroded surface of the Hercynides, creating a second structural layer of slightly disturbed beds.

To the east of Zlatoust stand out: 1) the western greenstone zone, stretching to the west of the city of Miass; 2) the central zone of serpentines, granites and siliceous schists of the Carboniferous - from Miass to st. Poletaevo and 3) the eastern zone of greenstone rocks and granites - from st. Poletaevo to Chelyabinsk.

Within the western greenstone belt on the eastern slope of the Southern Urals, folds are developed that are overturned and pushed to the west over the Precambrian crystalline schists in the vicinity of Zlatoust. In the cores of the folds lie serpentines, and trudged with gabbro and diorite. The most ancient rocks of the folds are Silurian and Lower Devonian diabases and pyroxenite porphyrites, accompanied by tuffs, siliceous schists and jaspers. Above them, they are replaced by Middle Devonian effusive albitophyres, quartz-plagioclase and pyroxene porphyrites, and conglomerates with pebbles of previous gabbro and diorites. Even higher in the section, there is a thick Upper Devonian siliceous shale layer overlain by greywackes. They are covered with Visean limestones. The central zone of serpentines is intensively deployed throughout; it contains preserved bands of pyroxene porphyrites and their Devonian tuffs. The Hercynian granite-gneiss massif of the Ilmensky Mountains belongs to this zone, with which miaskites are associated - alkaline granites.

The eastern greenstone zone composes wide areas to the west of the city of Chelyabinsk. Diabases, pyroxene-plagioclase porphyrites, tuffs, tuffites with subordinate siliceous schists and red jaspers are intensively dislocated here. These rocks in the period from the Silurian to the Middle Devonian were intruded by gabbro, later by granodiorites and granites. The latter are cataclased and transformed into granite-gneisses. The intrusion of granitic magma was associated with hydrothermal solutions that caused the formation of arsenic, tungsten and gold deposits.

The comprehensive geological and geophysical studies carried out in recent years on the territory of the Southern Urals and the adjacent eastern margin of the Russian platform have shed new light on the structure of deep regions of the earth's crust. It turned out to be possible to distinguish two zones within the Ural folded region: outer and inner.

The outer one occupies most of the western slope of the Southern and Middle Urals and is characterized by the same magnetic and gravitational anomalies that were found on the adjacent parts of the Russian platform and in the Cis-Ural foredeep.

The inner zone covers the entire slope of the Urals with its magnetic and gravitational properties, reflecting the features of the deep structure.

Magnetic and gravitational anomalies in the outer zone can be interpreted in the sense that the crystalline basement in the region of the western slope of the Urals plunges sharply to 11-16 km instead of 4-6 km under the Russian platform. Seismic data revealed a smaller subsidence of basalt and peridotite "layers" in the same West Slope. This contradiction is explained by a decrease to 7-10 km in the thickness of the granite "layer" within the Western slope and Cis-Ural trough.

The transition from the outer to the inner zone, as F. I. Khatyanov (1963) points out, is expressed by a band of high gradients of averaged gravity anomalies. It sort of separates the West Ural gravity minimum from the East Ural maximum. Here the basalt "layer" rises by 6-10 km, and the granite one becomes much thinner, so that it approaches the oceanic type. In this band, it is possible to expect a deep fault, which is the eastern boundary of the crystalline substrate of the Russian platform, which, therefore, lies at the base of the Western slope of the Urals (outer zone). F. I. Khatyanov suggests that, due to such a structure of the Western slope, it is structurally closer to the platform. He even suggests a name - folded platform zone. The true geosyncline is the Eastern Urals with its powerful magmatism, intense folding and strong metamorphism.

Cycles and phases of tectogenesis. The structure of the Urals took shape over an extremely long period of time under the influence of the Salair, Caledonian, Hercynian, Cimmerian and Alpine cycles of tectogenesis. The most important were the Paleozoic cycles, which created the huge, complexly folded Ural structure; the Mesozoic and Cenozoic cycles manifested themselves in the form of faults and multiple block movements; they did not change the main folded structure and formed only the external geomorphological appearance of the Urals. The sharp difference in the degree of metamorphism of the Lower Paleozoic strata and underlying crystalline schists and quartzites indicates the existence of isolated fields of Precambrian rocks in different parts of the Urals. The gradual transition of these rocks to the rocks of the Lower Paleozoic is now denied by most researchers.

The Salair tectogenesis is most reliably established for the region of the Beloretsk plant, where the Ordovician lies at the base on quartzites, shales, and limestones with algae and, possibly, Middle Cambrian archaeocyates, inconsistent with the basal conglomerate. The precipitation of the Upper Cambrian was also observed in the basin of the river. Sakmary. Its absence represents, according to D.V. Nalivkin, a widespread phenomenon: the Upper Cambrian falls out of the section in the Baltic, on Novaya Zemlya, in the Urals, in the Tien Shan, in the Kazakh steppe, in Altai, in the Kuznetsk basin, in a number of places in the Siberian platforms. This is the result of the Salairian folding, which some geologists attribute to the Caledonian cycle. The Caledonian tectogenesis manifested itself throughout the region of the Western Urals; it was also proved for Mugodzhar. It was accompanied not only by the formation of folds, but also by the intrusion of magma: the granites of the Troitskoye deposit on the Western slope of the Middle Urals and in the south of Mugodzhary, in the Southern Urals, are considered Caledonian. Starting from Mugodzhary to the northernmost extremities of the Urals, conglomerates and sandstones of the Middle and Upper Devonian usually contain fragments and pebbles of various Lower Paleozoic and Precambrian sedimentary and. This shows that the Devonian Sea transgressed onto a landform developed in the folded Lower Paleozoic, whose structures included Caledonian granites and Precambrian rocks. For Mugodzhar and Timan, it is quite established that the Caledonian tectogenesis was manifested by folding, magma intrusions and uplifts with the appearance of land, on which the relief began to develop. In some areas of the Southern and Northern Urals, the Caledonian tectogenesis is judged by the overlapping of the continental Lower Devonian on the marine Upper Silurian; in some places the Lower Devonian is completely absent.

The Hercynian tectogenesis has been established in the Urals for the longest time. This cycle expressed itself with great force and intensity on the Eastern slope of the Urals; in the West, however, it manifested itself with moderate intensity, often even weakly over large areas.

A complete stratigraphic section from the Upper Devonian to the Lower Carboniferous in the Urals indicates the absence of the Breton phase. On the Western slope, the Etren type fauna is observed, which is a mixture of Devonian and Carboniferous forms.

The Sudeten phase on the Eastern Slope of the Urals can be judged by a sharp change in the lithological composition at the base of the Middle Carboniferous, where thick coarse clastic conglomerates and sandstones are established; D. V. Nalivkin rightly notes that this change indicates the uplift that began then not within the Eastern slope of the Urals, but somewhere to the east of it; the mountainous country here rose and, entering the conditions of the denudation regime, quickly collapsed; the products of destruction were conglomerates and sandstones deposited in the Eastern slope of the Urals. On the Western slope, limestones of the Lower Carboniferous usually gradually pass into limestones of the Middle Carboniferous, the latter without interruption and unconformity pass into the Upper Carboniferous; this indicates the absence of manifestations of the Sudeten and Asturian phases here.

The Asturian phase manifested itself on the Eastern Slope of the Urals, where the Upper Carboniferous deposits completely fall out of the section due to uplifts that engulfed the territory of the Eastern Slope by the beginning of the Upper Carboniferous. Since then, the region of the Eastern Slope of the Urals has become a place of intense tectonic movements that have created extremely complex structures. From the beginning of the Permian period, the eastern and central zones (bands) of the Urals turn into a powerful mountain range; simultaneously with the formation processes, it immediately began to collapse, giving a huge amount of clastic material, which was carried to the territory of the Western Slope, where the marine regime continued to be maintained in the resulting trough; that is why it is so difficult to draw a line between the Carboniferous and the Permian.

Cimmerian tectogenesis was expressed by the dislocation of Mesozoic coal-bearing deposits in the Chelyabinsk region. Based on the remains of the flora, it was possible to determine that a significant part of these deposits belong to the Upper Triassic; folds of the coal-bearing strata are unconformably overlain by undisturbed Upper Cretaceous and Paleogene accumulations. When studying the morphological structure of the Chelyabinsk basin, microfolds are found in it - platy, overturned, pointed-beak-shaped; they give the structure a crumpled character; the greatest dislocation is observed at the sides, where the Mesozoic layers are adjacent to the Paleozoic massifs; with distance from the sides of the massifs, the folding dies out. Mesozoic deposits, as mentioned earlier, are concentrated in deep grabens among Paleozoic rock massifs.

The nature of the Cimmerian structures shows that the Cimmerian folding that gave rise to them is passive, resulting from the crushing of loose Mesozoic deposits by Paleozoic blocks into small overturned, isoclinal, sometimes broken folds. The probability of such an explanation is also confirmed by the locality of the Mesozoic folding.

In the Chelyabinsk basin, it is the result of landslides of the Mesozoic age, simultaneous with the deposition of sediments and occurring along the banks or at the bottom of the corresponding water basins. Alpine tectogenesis in the Urals was manifested by blocky movements of Paleozoic massifs. Occasionally occurring local folds in the Chelyabinsk and Lozvinsk regions are caused by these movements. They also created the following, now observed, geomorphological features of the Urals: the storey arrangement of leveling surfaces; redevelopment of a parallel-linear river network to a cranked-composite one; the formation of two watersheds; a sharp difference between ancient and modern river systems; hanging valleys; high terraces on Akchagyl sandy-argillaceous deposits; rejuvenation of river valleys. Due to young faults, the Neogene rocks of the Urals lie at different heights, and weak earthquakes occur in the north of the Ufimsky plateau, which are noted by the Sverdlovsk geophysical observatory.

Relief formation. The study of ancient platforms has revealed a remarkable stability of tectonic structures. Most of them, being founded at the end of the Precambrian - the beginning of the Paleozoic, still exist, changing only in their outlines and sizes. Large geomorphological elements, which are usually tectonomorphic, have the same stability. At the same time, the modern tectonic structure and modern relief of both platforms were formed by neotectonic movements that began in the Neogene. They manifested themselves mainly radially in ups and downs, which was formerly called epirogenesis. However, the presence of folded, tangential formations of a large radius of curvature began to be detected more and more often.

Turning now to the study of the large Ural fold system of the Paleozoic, we find the same most characteristic tectonic and geomorphological features, expressed even more clearly. Manifestations of neotectogenesis are observed especially with great efficiency in the post-Cambrian folded areas. It is to him that these areas owe their revival after the peneplanization of the mountainous relief. However, in different folded areas, the degree of mobility turned out to be unequal, and therefore the restored (regenerated) mountains are divided into: a) weakly mobile - of the Ural type; b) mountains of the Tyanypan-Baikal type of very high mobility, restored on the site of the Epi-Cambrian, Epi-Caledon, Epi-Hercynian platforms; c) mountains of the Verkhoyansk-Kolyma type, also of considerable mobility, but rising on the site of Mesozoic folding; d) mountains of the Caucasian-Pamir type in the belt of the Mesozoic-Cenozoic orogeny. In all these types, with very different hypsometry, structural and geomorphological features turn out to be common.

Neotectogenesis inherited all the main structures created in the geosynclinal stages, their regional revitalized faults, including deep ones, which limited the blocks, making them distinct in the modern one.

The structures of the Urals, developed on the site of the Caledonian and Hercynian geosynclinal furrows, after orogeny were also orographic elements: ridges were confined to anticlinoria, depressions - synclinoria, sharp relief drops - ledges - to the lines of large faults. In Mesozoic times, these structures and the tectonomorphic relief experienced peneplanation, and the synclinal depressions were filled with proluvial, alluvial, and lacustrine deposits, the material for which was the destruction products of neighboring uplifts. The rather significant thickness of these accumulations speaks of structures continuing to develop posthumously already in the platform setting. By the end of the Mesozoic, denudation reduced the Urals to an almost flat plain with a well-developed relief and wide valleys oriented meridionally, i.e., along the strike of the main structures. But in the Neogene, neotectonic movements of a differentiated nature with uplifts and subsidences of considerable amplitude appeared. The inherited Mesozoic relief with a longitudinal hydrographic network began to be rebuilt; relief received a general rejuvenation. The longitudinal parallel-linear river network turned into an elbow-composite one, since new valleys were obtained by joining two or more independent valleys through the formation of transverse, epigenetic elbows. Tectonic cracks played a significant role in this. But, despite these rearrangements of the relief, its tectonomorphism and heredity have been preserved to the present, which is so clearly expressed in the meridional strike of the ridges, subordinate to the strike of the structures.

Along with distinctly pronounced blocky vertical movements, observations more and more reliably point to wave arched uplifts, i.e., large-radius folding of the dislocated base.

The magnitude of the uplift of the Ural Mountains under the influence of neotectogenesis, in other words, for the time since the Neogene, can be judged approximately: for the Southern Urals, uplifts of 700-800 m are allowed, for the Middle Urals (the basin of the Chusovaya River) - 200-300 m, for the Northern - 500-800 m It is remarkable that the positive structures (anticlinorium, horsts) rise more than the negative ones (synclinorium, grabens).

To the south, the Ural Paleozoic structures submerge, appearing on the surface as the Chushkakul uplift.

In general, neotectonic movements in the Urals are not great, which led to its mid-mountain relief and weak seismicity, confined to the Middle Urals and not exceeding 6 points in strength. For the earthquake of August 17, 1914, a map of isoseisms was compiled, which give a northwest-southeast orientation at an angle to the meridional strike of the structures.

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The system of low- and medium-altitude mountain ranges of the Urals stretches along the eastern outskirts of the Russian (East European) Plain in a submeridional direction from the coast of the Arctic Ocean to the southern borders of Russia. This mountain range, a stone belt ("Ural" in translation from the Turkic and means "belt") is sandwiched between two platform plains - East European and West Siberian. The natural continuation of the Urals in the geological and tectonic terms in the south are the Mugodzhary Islands, and in the north the islands of Vaigach and Novaya Zemlya. Some authors unite them together with the Urals into a single Ural-Novaya Zemlya physical-graphic country (Rikhter G.D., 1964; Alpatiev A.M., 1976), others include only Mugodzhary in the Ural mountainous country (map "Physical-geographical zoning of the USSR", 1983 ; Makunina A.A., 1985; Davydova M.I. et al., 1976, 1989), the third do not include either one or the other (Milkov F.N., Gvozdetsky N.A., 1986). According to our scheme of physical-geographical zoning of Russia, Novaya Zemlya belongs to the island Arctic, and the question of Mugodzhary, located in Kazakhstan, does not arise at all.

Rice. 8. Orographic scheme of the Urals.

Being a clearly defined natural boundary between the two largest lowland countries, the Urals at the same time does not have distinct borders with the Russian Plain. The plain gradually turns into low and elevated hilly-ridged foothills, which are further replaced by mountain ranges. Usually the border of the Ural mountain country is drawn along Cis-Ural foredeep, genetically associated with the formation of a mountain structure. Approximately, it can be drawn along the river valley Korotaihi, further down the river Adzwa- the tributary of the Usa and along the Usa itself, separating the Chernyshev Ridge from the Pechora Lowland, along the submeridional segment of the valley Pechory, lower reaches Vishera, just east of the valley Kama, downstream of the river Sylva, along submeridional sections of the river Ufa and White, further south to the Russian border. The eastern border of the Urals starts from Baidaratskaya Bay Kara Sea and is more pronounced. In the northern part, the mountains rise in a steep ledge above the flat swampy plain of Western Siberia. The strip of foothills here is very narrow, only in the region of Nizhny Tagil it expands significantly, including the Trans-Ural peneplain and in the south the Trans-Ural plateau.

The Ural mountain country stretches from north to south for more than 2000 km from 69° 30" N to 50° 12" N. It crosses five natural zones of Northern Eurasia - tundra, forest-tundra, taiga, forest-steppe and steppe. The width of the mountain belt is less than 50 km in the north, and over 150 km in the south. Together with the foothill plains that make up the country, its width varies from 50-60 km in the northern part of the region to 400 km in the south.

The Urals has long been considered the border between two parts of the world - Europe and Asia. The border is drawn along the axial part of the mountains, and in the southeast along the Ural River. In natural terms, the Urals are closer to Europe than to Asia, which is facilitated by its pronounced asymmetry. To the west, towards the Russian Plain, the mountains gradually decrease, in a series of low ridges and ridges with gentle slopes, passing into foothill plains, which have a significant similarity with the adjacent parts of the Russian Plain. Such a transition also ensures a gradual change in natural conditions with the preservation of some of their properties in mountainous regions. In the east, as already noted, the mountains, for a significant part of their length, abruptly break off to low and narrow foothills, so the transitions between the Urals and Western Siberia are sharper and more contrasting.

Many Russian and Soviet naturalists and scientists took part in the study of the Urals. One of the first explorers of the nature of the Southern and Middle Urals was the head of the mountain state-owned Ural factories, the founder of Yekaterinburg, Perm and Orenburg, a prominent statesman from the time of Peter I, historian and geographer V.N. Tatishchev (1686-1750). In the second half of the XVIII century. a great contribution to the study of the Urals was made by P.I. Rychkov and I.I. Lepekhin. In the middle of the 19th century, the geological structure of the Ural Mountains was studied almost throughout their entire length by Professor of St. Petersburg University E.K. Hoffmann. A great contribution to the knowledge of the nature of the Urals was made by Soviet scientists V.A. Varsanofiev, P.L. Gorchakovsky, I.M. Krasheninnikov, I.P. Kadilnikov, A.A. Makunina, A.M. Olenev, V.I. Prokaev, B.A. Chazov and many others. The geological structure and relief have been studied in particular detail, since it was the riches of the bowels of the Urals that made it famous as an underground pantry of the country. A large team of scientists was engaged in the study of the geological structure and minerals: A.P. Karpinsky, F.N. Chernyshev, D.V. Nalivkin, A.N. Zavaritsky, A.A. Bogdanov, I.I. Gorsky, N.S. Shatsky, A.V. Peive and others.

At present, the nature of the Urals is quite well studied. There are several thousand sources from which you can draw information about the nature of the Urals, which allows you to characterize the region and its individual parts in great detail.

History of development and geological structure

The history of the development of the Urals determined the presence of two significantly different complexes (structural tiers) in the structure of folded structures. The lower complex (stage) is represented by pre-Ordovician sequences (AR, PR and Є). The rocks of this complex are exposed in the cores of large anticlinoria. They are represented by various gneisses and Archean schists. Metamorphic schists, quartzites and marbles of the Lower Proterozoic are found in places.

Above these sequences are Riphean (Upper Proterozoic deposits), reaching a thickness of 10-14 km and represented by four series. All these series are characterized by rhythm. Conglomerates, quartz sandstones and quartzites occur at the base of each series, passing higher into siltstones, clayey and phyllite shales. At the top of the section, they are replaced by carbonate rocks - dolomites and limestones. Crowns the section of the Riphean deposits typical molasse(Asha series), reaching 2 km.

The composition of the Riphean deposits indicates that during their accumulation there was an intense subsidence, which was repeatedly replaced by short-term uplifts, leading to a facies change of deposits. At the end of the Riphean Baikal folding and uplifts began, which intensified in the Cambrian, when almost the entire territory of the Urals turned into land. This is evidenced by the very limited distribution of Cambrian deposits, represented only by Lower Cambrian green shales, quartzites and marbles, which are also part of the lower structural complex.

Thus, the formation of the lower structural stage ended with the Baikal folding, which resulted in the formation of structures that differ in plan from the later Ural structures. They continue with the basement structures of the northeastern (Timan-Pechora) margin of the East European Platform.

The upper structural stage is formed by sediments starting from the Ordovician and ending with the Lower Triassic, which are subdivided into geosynclinal (О-С2) and orogenic (С3-T1) complexes. These deposits accumulated in the Ural Paleozoic geosyncline and the folded area that arose within it. The tectonic structures of the modern Urals are associated with the formation of this particular structural stage.

Ural is an example of one of the largest linear folded systems stretching for thousands of kilometers. It is a meganticlinorium, which consists of alternating anticlinoria and synclinoria oriented in the meridional direction. In this regard, the Urals are characterized by exceptional constancy of the section along the strike of the fold system and rapid variability across the strike.

The modern structural plan of the Urals was laid already in the Ordovician, when all the main tectonic zones arose in the Paleozoic geosyncline, and the thickness of the Paleozoic deposits reveals a clear facies zonality. However, there are sharp differences in the nature of the geological structure and development of the tectonic zones of the western and eastern slopes of the Urals, which form two independent mega-zones. They are separated by a narrow (15-40 km) and very regular strike Uraltau anticlinorium(in the north it is called Harbeysky), bounded from the east by a large deep fault - Main Ural Fault, which is associated with a narrow band of outcrops of ultrabasic and basic rocks. In some places, the fault is a strip 10-15 km wide.

The eastern megazone, which is maximally sag and characterized by the development of basic volcanism and intrusive magmatism, developed in the Paleozoic as eugeosyncline. Thick strata (over 15 km) of sedimentary-volcanogenic deposits have accumulated in it. This megazone is part of the modern Urals only partially and, to a large extent, especially in the northern half of the Urals, is hidden under the Meso-Cenozoic cover of the West Siberian Plate.

Rice. 9. Scheme of tectonic zoning of the Urals (morphotectonic zones)

The western megazone is practically devoid of igneous rocks. In the Paleozoic it was miogeosyncline where the accumulation of marine terrigenous and carbonate deposits took place. In the west, this megazone passes into Cis-Ural foredeep.

From the point of view of supporters of the lithospheric plate hypothesis, the Main Ural Fault fixes the subduction zone of the oceanic plate moving from the east under the eastern color of the East European Platform. The Uraltau anticlinorium is confined to the marginal part of the platform and corresponds to an ancient island arc, to the west of which a subsidence zone on the continental crust (miogeosyncline) developed, to the east, the formation of the oceanic crust (up to the Middle Devonian), and later, the granite layer in the eugeosyncline zone.

At the end of the Silurian in the Ural geosyncline, Caledonian folding, which covered a significant territory, but was not the main one for the Urals. Already in the Devonian, the subsidence resumed. The main folding for the Urals was hercynian. In the eastern megazone, it occurred in the middle of the Carboniferous and manifested itself in the formation of strongly compressed, often overturned folds, thrusts, accompanied by deep splits and the intrusion of powerful granite intrusions. Some of them are up to 100-120 km long and up to 50-60 km wide.

The orogenic stage began in the Eastern Megazone from the Upper Carboniferous. The young fold system located here supplied clastic material to the marine basin, preserved on the western slope, which was a vast foothill trough. As the uplift continued, the trough gradually migrated to the west, towards the Russian plate, as if "rolling" on it.

The Lower Permian deposits of the western slope are diverse in their composition: carbonate, terrigenous and halogen, which indicates the retreat of the sea in connection with the ongoing mountain building in the Urals. At the end of the Lower Permian, it also spread to the western megazone. Folding here was less vigorous. Simple folds predominate, overthrusts are rare, and there are no intrusions.

Tectonic pressure, which resulted in folding, was directed from east to west. The basement of the East European Platform prevented the spread of folding, therefore, in the areas of its eastern ledges (Ufimsky horst, Usinsky arch), the folds are most compressed, and bends flowing around them are observed in the strike of the folded structures.

Thus, in the Upper Permian, already throughout the entire territory of the Urals, there was young fold system, which became the scene of moderate denudation. Even in the Cis-Ural foredeep, deposits of this age are represented by continental facies. In the far north, their accumulation dragged on until the Lower Triassic.

In the Mesozoic and Paleogene, under the influence of denudation, mountains were destroyed, lowered, and extensive leveling surfaces and weathering crusts were formed, with which alluvial mineral deposits are associated. And although the trend towards uplift of the central part of the country continued, which contributed to the exposure of Paleozoic rocks and the relatively weak formation of loose deposits, in the end, the downward development of the relief prevailed.

In the Triassic, the eastern part of the folded structures descended along the fault lines, i.e., the Ural folded system separated from the Hercynian structures of the basement of the West Siberian Plate. At the same time, a series of narrow submeridionally elongated graben-like depressions arose in the eastern megazone filled with continental clastic-volcanogenic sequences of the Lower-Middle Triassic ( Turin series) and the continental coal-bearing formation of the Upper Triassic, and in some places the Lower-Middle Jurassic ( Chelyabinsk series).

By the end of the Paleogene, in place of the Urals, a peneplain plain extended, more elevated in the western part and lower in the eastern part, periodically overlapped in the extreme east by thin marine deposits in the Cretaceous and Paleogene.

Rice. 10. Geological structure of the Urals

In the Neogene-Quaternary time, differentiated tectonic movements were observed in the Urals. Crushing and moving of individual blocks to different heights took place, which led to mountain revival. The western megazone, including the Uraltau anticlinorium, is more elevated almost throughout the entire length of the Urals and is characterized by mountainous terrain, while the eastern megazone is represented by a peneplain or small hills with separate mountain ranges (eastern foothills). Along with discontinuous dislocations, among which longitudinal faults played a leading role, latitudinal wave-like deformations also appeared in the Urals - part of similar waves of the East European and West Siberian plains (Meshcheryakov Yu.A., 1972). The consequence of these movements was the alternation of elevated (corresponding to wave crests) and lowered (corresponding to the sole) sections of mountains along their strike (orographic regions).

In the Urals, there is a clear correspondence geological structure structure of the modern surface. She is characterized longitudinal zonal structure. Six morphotectonic zones succeed each other from west to east. Each of them is characterized by its history of development, and, consequently, by deposits of a certain age and composition, a combination of minerals and relief features.

The Cis-Ural foredeep separates the folded structures of the Urals from the eastern edge of the Russian Plate. Transverse horst-like uplifts (Karatau, Polyudov Kamen, Chernysheva, Chernova) divide the trough into separate depressions: Belskaya, Ufimsko-Solikamskaya, North Ural (Pechora), Vorkuta (Usinskaya) and Karatakhskaya. The southern regions of the Belskaya depression are the most deeply submerged (up to 9 km). In the Ufimsko-Solikamsk depression, the thickness of the deposits that perform the trough decreases to 3 km, but again increases to 7-8 km in the Vorkuta depression.

The trough is made up of predominantly Permian sediments - marine (in the lower part) and continental (in the upper part of the section). In the Belsk and Ufimsko-Solikamsk depressions, in the deposits of the Lower Permian (Kungurian stage), a salt-bearing stratum up to 1 km thick is developed. To the north, it is replaced by coal-bearing.

The deflection has an asymmetric structure. It is deepest in the eastern part, where coarser deposits predominate along its entire length than in the western part. The deposits of the eastern part of the trough are crumpled into narrow linear folds, often overturned to the west. In the depressions where the Kungur salt-bearing stratum is developed, salt domes are widely represented.

Deposits of salts, coal and oil are associated with the marginal trough. In the relief, it is expressed by low and elevated foothill plains of the Cis-Urals and low parmas (ridges).

The synclinorium zone of the western slope (Zilairsky, Lemvilsky, etc.) directly adjoins the Cis-Ural marginal foredeep. It is composed of Paleozoic sedimentary rocks. The youngest of them - carbonaceous (mainly carbonate) are distributed in the western part, adjacent to the marginal foredeep. To the east, they are replaced by Devonian shales, Silurian carbonate strata, and rather strongly metamorphosed, with traces of volcanism, Ordovician deposits. Among the latter there are dikes of igneous rocks. The amount of volcanogenic rocks increases towards the east.

The synclinorium zone also includes the Bashkir anticlinorium, connected by its northern tip with the Uraltau anticlinorium, and in the south separated from it by the Zilair synclinorium. It is composed of layers of Riphean. In its structure, it is closer to the structures of the next morphotectonic zone, but territorially located in this zone.

This area is poor in minerals. There are only building materials here. In relief, it is expressed by short marginal ridges and massifs of the Urals, High Parma and the Zilair plateau.

The Uraltau anticlinorium forms the axial, highest part of the mountain structure of the Urals. It is composed of rocks of the pre-Ordovician complex (lower structural stage): gneisses, amphibolites, quartzites, metamorphic schists, etc. Strongly compressed linear folds are developed in the anticlinorium, overturned to the west or east, which gives the anticlinorium a fan-shaped structure. Along the eastern slope of the anticlinorium runs Main Ural deep fault, which is associated with numerous intrusions of ultramafic rocks. A large complex of minerals is associated with them: deposits of nickel, cobalt, chromium, platinum, Ural gems. Iron deposits are associated with the thickness of the Riphean deposits.

In the relief, the anticlinorium is represented by a narrow meridionally elongated ridge. In the south it is called Uraltau, to the north - the Ural Range, even further - Poyasovy Stone, Research, etc. This axial ridge has two bends to the east - in the area of the Ufimsky horst and the Bolshezemelsky (Usinsky) arch, that is, where it goes around the rigid blocks of the Russian plate.

The Magnitogorsk-Tagil (Zelenokamenny) synclinorium stretches along the entire Urals up to the coast of Baydaratskaya Bay. It is composed of the Ordovician-Lower Carboniferous sedimentary-volcanogenic complex. Diabases, diabase-porphyries, tuffs, various jaspers (green, meat-red, etc.), extensive acidic intrusive bodies (trachytes, liparites), and in some places very strongly metamorphosed limestones (marbles) are widespread here. In the fault zones that limit the synclinorium, there are intrusions of ultramafic rocks. All rocks are strongly sheared. Often the rocks have undergone hydrothermal alteration. This is - copper pyrite strip, where there are hundreds of copper deposits. Deposits of iron ore are confined to the contact of granites with limestones of the Lower Carboniferous. There is placer gold and Ural gems (precious and semi-precious stones).

In the relief, this zone is represented by short ridges and individual massifs up to 1000-1200 m high and higher, located among vast depressions along which river valleys are laid.

The Ural-Tobolsk, or East Ural, anticlinorium can be traced along the entire folded structure, but only its southern part is included in the Ural mountainous country, since north of Nizhny Tagil it is hidden under the cover of the Meso-Cenozoic cover of the West Siberian plate. It is composed of shale and volcanogenic strata of the Paleozoic and Riphean, penetrated by intrusions of granitoids, predominantly of the Upper Paleozoic age. Sometimes the intrusions are enormous. They are associated with deposits of high quality iron and gold. Short chains of ultramafic intrusions are also traced here. Ural gems are widespread.

In the relief, the anticlinorium is represented by a ridged strip of the eastern foothills and the Trans-Ural peneplain.

The Ayat synclinorium is part of the Urals only with its western wing in the extreme south of the region. To the north and east it is overlain by the Meso-Cenozoic sedimentary cover. The siclinorium is composed of heavily crushed and crumpled Paleozoic deposits, intruded by igneous rocks of various compositions, protruding from under the cover of Paleogene deposits. Narrow graben-like depressions are developed here, filled with Triassic and Lower Jurassic deposits of the Turin and Chelyabinsk series. Coal deposits are associated with the latter. In the relief, the Ayat synclinorium is presented as part of the Trans-Ural plateau.

Thus, the morphotectonic zones of the Urals differ from each other in their geological structure, relief and a set of minerals, so the natural zonal structure of the Urals is perfectly readable not only on a geological map, but also on mineral and hypsometric maps.

Russia and the countries of the former USSR (with geographical and biological semantic captions for photographs) can be found in the "Europe" and "Asia" sections of the "Natural landscapes of the world" section of our site.

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For a better understanding of what is written, see also " Dictionary of physical geography", which has the following sections:

Above these sequences are Riphean (Upper Proterozoic deposits), reaching a thickness of 10-14 km and represented by four series. A feature of all these series is rhythm. Conglomerates, quartz sandstones and quartzites occur at the base of each series, passing higher into siltstones, clayey and phyllite shales. At the top of the section, they are replaced by carbonate rocks - dolomites and limestones. The section of the Riphean deposits is crowned by a typical molasse (Asha Series), reaching 2 km.

The composition of the Riphean deposits indicates that during their accumulation there was an intense subsidence, which was repeatedly replaced by short-term uplifts, leading to a facies change of deposits. At the end of the Riphean, Baikal folding occurred and uplifts began, which intensified in the Cambrian, when almost the entire territory of the Urals turned into land. This is evidenced by the very limited distribution of Cambrian deposits, represented only by Lower Cambrian green shales, quartzites and marbles, which are also part of the lower structural complex.

The Urals is an example of one of the large linear fold systems stretching for thousands of kilometers. It is a meganticlinorium, which consists of alternating anticlinoria and synclinoria oriented in the meridional direction. In this regard, the Urals are characterized by exceptional constancy of the section along the strike of the fold system and rapid variability across the strike.

The modern structural plan of the Urals was laid already in the Ordovician, when all the main tectonic zones arose in the Paleozoic geosyncline, and the thickness of the Paleozoic deposits reveals a clear facies zonality. However, there are sharp differences in the nature of the geological structure and development of the tectonic zones of the western and eastern slopes of the Urals, which form two independent mega-zones. They are separated by a narrow (15-40 km) Uraltau anticlinorium, which is very consistent along the strike (in the north it is called the Harbeisky one), bounded from the east by a large deep fault - the Main Ural Fault, to which a narrow strip of outcrops of ultrabasic and basic rocks is confined. In some places, the fault is a strip 10-15 km wide.

The eastern megazone, which is maximally concave and characterized by the development of basic volcanism and intrusive magmatism, developed in the Paleozoic as a eugeosyncline. It accumulated powerful strata (over 15 km)

Rice. 9. Scheme of tectonic zoning of the Urals (morphotectonic zones) of sedimentary-volcanogenic deposits. This megazone is part of the modern Urals only partially and, to a large extent, especially in the northern half of the Urals, is hidden under the Meso-Cenozoic cover of the West Siberian Plate.

The western megazone is practically devoid of igneous rocks. In the Paleozoic, it was a miogeosyncline, where marine terrigenous and carbonate deposits accumulated. In the west, this megazone passes into the Cis-Ural marginal foredeep.

At the end of the Silurian, the Caledonian folding occurred in the Ural geosyncline, which covered a significant territory, but was not the main one for the Urals. Already in the Devonian, the subsidence resumed. The main folding for the Urals was the Hercynian. In the eastern megazone, it occurred in the middle of the Carboniferous and manifested itself in the formation of strongly compressed, often overturned folds, thrusts, accompanied by deep splits and the intrusion of powerful granite intrusions. Some of them are up to 100-120 km long and up to 50-60 km wide.

coformation here was less vigorous. Simple folds predominate, overthrusts are rare, and there are no intrusions.

Thus, in the Upper Permian, a young folded system already existed throughout the entire territory of the Urals, which became the scene of moderate denudation. Even in the Cis-Ural foredeep, deposits of this age are represented by continental facies. In the far north, their accumulation dragged on until the Lower Triassic.

In the Triassic, the eastern part of the folded structures descended along the fault lines, i.e., the Ural folded system separated from the Hercynian structures of the basement of the West Siberian Plate. At the same time, a series of narrow submeridionally elongated graben-like depressions arose in the eastern megazone, filled with continental clastic-volcanogenic sequences of the Lower-Middle Triassic (Turin Group) and the continental coal-bearing formation of the Upper Triassic, and in places of the Lower-Middle Jurassic (Chelyabinsk Series).

By the end of the Paleogene, in place of the Urals, a peneplain plain extended, more elevated in the western part and lower in the eastern, periodically

overlain in the extreme east by thin marine deposits in the Cretaceous and Paleogene.

Rice. 10. Geological structure of the Urals

In the Neogene-Quaternary time, differentiated tectonic movements were observed in the Urals. There was a crushing and movement of individual blocks to different heights, which led to the revival of the mountains. The western megazone, including the Uraltau anticlinorium, is more elevated almost throughout the entire length of the Urals and is characterized by mountainous terrain, while the eastern megazone is represented by a peneplain or small hills with separate mountain ranges (eastern foothills). Along with discontinuous dislocations, among which longitudinal faults played a leading role, latitudinal wave-like deformations also appeared in the Urals - part of similar waves of the East European and West Siberian plains (Meshcheryakov Yu.A., 1972). The consequence of these movements was the alternation of elevated (corresponding to wave crests) and lowered (corresponding to the sole) sections of mountains along their strike (orographic regions).

In the Urals, the correspondence of the geological structure to the structure of the modern surface is clearly traced. It is characterized by a longitudinal-zonal structure. Six morphotectonic zones succeed each other from west to east. Each of them is characterized by its history of development, and, consequently, by deposits of a certain age and composition, a combination of minerals and relief features.

Deposits of salts, coal and oil are associated with the marginal trough. In the relief, it is expressed by low and elevated foothill plains of the Cis-Urals and low parmas (ridges).

This area is poor in minerals. There are only building materials here. In relief, it is expressed by short marginal ridges and massifs of the Urals, High Parma and the Zilair plateau.

The Uraltau anticlinorium forms the axial, highest part of the mountain structure of the Urals. It is composed of rocks of the pre-Ordovician complex (lower structural stage): gneisses, amphibolites, quartzites, metamorphic schists, etc. Strongly compressed linear folds are developed in the anticlinorium, overturned to the west or east, which gives the anticlinorium a fan-shaped structure. Along the eastern slope of the anticlinorium runs the Main Ural Deep Fault, which is associated with numerous intrusions of ultramafic rocks. A large complex of minerals is associated with them: deposits of nickel, cobalt, chromium, platinum, Ural gems. Iron deposits are associated with the thickness of the Riphean deposits.

The Magnitogorsk-Tagil (Zelenokamenny) synclinorium stretches along the entire Urals up to the coast of Baydaratskaya Bay. It is composed of the Ordovician-Lower Carboniferous sedimentary-volcanogenic complex. Diabases, diabase-porphyries, tuffs, various jaspers (green, meat-red, etc.), extensive acidic intrusive bodies (trachytes, liparites), and in some places very strongly metamorphosed limestones (marbles) are widespread here. In the fault zones that limit the synclinorium, there are intrusions of ultramafic rocks. All rocks are strongly sheared. Often the rocks have undergone hydrothermal alteration. This is a copper-pyrite strip, where there are hundreds of copper deposits. Deposits of iron ore are confined to the contact of granites with limestones of the Lower Carboniferous. There is placer gold and Ural gems (precious and semi-precious stones).

In the relief, this zone is represented by short ridges and individual massifs up to 1000-1200 m high and higher, located among vast depressions along which river valleys are laid.

In the relief, the anticlinorium is represented by a ridged strip of the eastern foothills and the Trans-Ural peneplain.

The Ayat synclinorium is part of the Urals only with its western wing in the extreme south of the region. To the north and east it is overlain by the Meso-Cenozoic sedimentary cover. The siclinorium is composed of heavily crushed and folded Paleozoic deposits, intruded by igneous rocks of various compositions, protruding from under the cover of Paleogene deposits. Narrow graben-like depressions are developed here, filled with Triassic and Lower Jurassic deposits of the Turin and Chelyabinsk series. Coal deposits are associated with the latter. In the relief, the Ayat synclinorium is presented as part of the Trans-Ural plateau.

Relief

In the relief of the Urals, two bands of foothills (western and eastern) and a system of mountain ranges located between them, elongated parallel to each other in a submeridional direction, are clearly distinguished, corresponding to the strike of tectonic zones. There may be two or three such ridges, but in some places their number increases, up to six or eight. The ridges are separated from each other by extensive depressions along which rivers flow. As a rule, ridges correspond to anticlinal folds composed of older and more durable rocks, while depressions correspond to synclinal ones.

The Ural Mountains are not high. Only some of their peaks exceed 1500 m. The highest point of the Urals is Mount Narodnaya (1895 m). Along the strike of the mountains, there is an alternation of elevated and lowered areas, due to undulating deformations of the Neogene-Quaternary period. This makes it possible to single out several orographic regions within the Urals, replacing each other when moving from north to south.

Rice. 11. Schematic diagram of the structure of the main structural elements of the Urals (according to A.S. Perfilyev and N.P. Kheraskov)

Pai-Khoi stretches from the Yugorsky Shar Strait to the valley of the Kara River in a southeasterly direction. It is a separate isolated ridges and hills with heights up to 400-450 m (mountain Moreiz - 467 m), rising among the low plains.

The Polar Ural starts from Mount Konstantinov Kamen and ends at the headwaters of the Khulga River. The ridges here have a southwestern strike, average heights are 600-800 m, but some peaks rise above 1000 m. The highest point is Mount Payer (1492 m).

The Subpolar Urals is located between the upper reaches of the Khulga River and the latitudinal segment of the Shchugor River. This is the highest part of the Urals, a mountain junction within which the mountain system changes its direction from southwestern to submeridional. It is represented by large fragmented arrays. Several peaks have heights of more than 1600 m: Mount Karpinsky (1662 m), Neroika (1646 m), Belfry (1649 m). Here is the highest point of the Urals - Mount Narodnaya.

The Northern Ural begins with Mount Telpoziz and ends with Konzhakovsky Stone (1569 m). The height of the ridges here is less than in the Subpolar Urals and averages up to 1000 m, but increases in the northern and southern parts.

The Middle Urals stretches up to Yurma Mountain. This is the lowest part of the mountains. The average heights here are 500-600 m. Only Mount Oslyanka in its northern part reaches 1119 m, all other peaks are below 1000 m. The mountains here form an arc, slightly curved to the east.

The Southern Urals starts from Mount Yurma and stretches to the southern borders of Russia. This is the widest and second highest part of the mountains. The ridges in the northern part are the highest (up to 1200-1600 m) and have a southwestern strike, which is replaced by meridional to the south. To the south, the mountains decline. The highest points are the mountains Yamantau (1638 m) and Iremel (1582 m).

The dominant type of morphostructures of the Urals are the revived fold-block mountains on the pre-Paleozoic and Paleozoic base. There are morphostructures that are transitional from folded to platform areas: plateaus (South Ural peneplain), socle ridge elevations (Pai-Khoi) and socle plains (Trans-Ural peneplain). Plat-

shaped structures are represented by stratified plains of the Cis-Ural foredeep and a plateau (Trans-Ural plateau).

Morphostructures created under the combined influence of endogenous and exogenous processes are complicated by smaller relief forms created by exogenous relief-forming processes. The imposition of various morphosculptures on morphostructures creates all the diversity of the relief of the Urals.

As in most mountainous regions, erosional relief prevails in the Urals. The main erosional forms here are river valleys. The Urals are characterized by the displacement of the main watershed ridge to the east of the axial part of the mountains, which is one of the manifestations of the asymmetry of the mountain structure. The most complex hydrographic pattern and the greater density of the river network are characteristic of the western slope of the mountains.

Many rivers were laid down during the period of the downward development of the mountains and the formation of the ancient leveling surface. They were confined to synclinal troughs, to bands of softer, more pliable rocks, therefore they had a general Ural, submeridional direction. During the period of activation of Neogene-Quaternary movements, the formation of faults and differentiated uplifts of predominantly small amplitude, transverse segments of river valleys were formed, confined to faults or depressions of the axes of anticlinal folds. Therefore, many rivers of the Urals have a cranked pattern: Ural, Sakmara, Belaya, Ai, Kosva, Vishera, Pechora, Ilych, Shchugor, etc. In longitudinal depressions they have wide valleys, and when crossing mountain ranges they are narrow and steep.

The rivers of the eastern slope (Ob basin) are shorter and more heavily incised. They are younger and have up to four or five terraces, while more; the ancient rivers of the western slope in the Cis-Urals have up to eight or nine terraces.

A characteristic feature of the Ural relief is the presence of ancient leveling surfaces raised to different heights. Therefore, flat-topped or dome-shaped ridges and massifs predominate here,

depending on their height. I.M. also wrote about the alignment surface. Krasheninnikov (1917, 1927). V.A. Varsanofiev (1932). Later, many researchers studied them in different parts of the Urals. However, there is still no consensus on either the number or age of these surfaces. Different researchers in different parts of the Urals, and sometimes in the same territory (for example, the Southern Urals) distinguish from one to seven surfaces.

Some authors (I.P. Gerasimov and others) believe that during the Jurassic-Paleogene a single leveling surface was formed here, which was raised to different heights by the latest movements of different amplitudes. Other authors do not agree that for such a long time there was only one undisturbed cycle of denudation. They tend to consider the high surface the most ancient, and the lowest - the Paleogene. However, the highest leveling surface in the northern part of the mountains, and sometimes in the Southern Urals, lies above the modern forest boundary or near it, i.e., at heights where denudation processes proceeded very vigorously in the Pleistocene and continue into the Holocene. Therefore, it can hardly be considered very ancient, especially since it usually lacks even the roots of weathering crusts.

In the highest parts of the mountains, modern bald processes are active (frost weathering, solifluction), so the peaks are covered with placers of stones (stone seas), sometimes tongues descending down the slopes (stone rivers). The cloak of clastic material reaches 2 - 5 m in thickness. On the slopes, goltsovye upland terraces are developed, which give the slopes a stepping. The height of upland terraces ranges from several meters to several tens of meters, width - from 20-30 to 200-300 m, and length - from tens of meters to 1.5-2 km. Often small terraces complicate the ledges of large ones.

Glacial (alpine) landforms in the Urals are very rare. They are typical only for the most elevated parts of the Subpolar and Polar Urals, where there is modern glaciation, but ancient glacial cirques, cirques and hanging valleys are also found in the Northern Urals up to 61 ° N.L. Whether there was an ancient mountain glaciation in the Southern Urals is not known for certain. However, the presence of two ancient cars is noted on the Zigalga Ridge.

For the western slope and Cis-Urals, where soluble rocks (limestones, dolomites, gypsum-bearing and salt-bearing strata) are widespread, karst relief forms are characteristic. These are numerous funnels, and dry valleys, and caves. Large caves are Divya, Kapova, Salavatskaya, Askinskaya and others. The Kungur Ice Cave, formed in Permian gypsum and anhydrite, with numerous grottoes, ice stalactites and stalagmites, and underground lakes is very famous.

The Ural Mountains were formed in the late Paleozoic during the era of intensive mountain building (Hercynian folding). The formation of the Ural mountain system began in the late Devonian (about 350 million years ago) and ended in the Triassic (about 200 million years ago).

It is an integral part of the Ural-Mongolian folded geosynclinal belt. Within the Urals, deformed and often metamorphosed rocks of predominantly Paleozoic age come to the surface. The strata of sedimentary and volcanic rocks are usually strongly folded, disturbed by ruptures, but in general they form meridional bands, which determine the linearity and zonality of the structures of the Urals. From west to east stand out:

- Cis-Ural marginal foredeep with a relatively gentle sedimentation in the western side and more complex in the eastern side;
- zone of the western slope of the Urals with the development of intensely folded and disturbed by thrust sedimentary strata of the lower and middle Paleozoic;
- Central Ural uplift, where among the sedimentary strata of the Paleozoic and Upper Precambrian, older crystalline rocks of the edge of the East European Platform come out in places;
- a system of troughs-synclinories of the eastern slope (the largest are Magnitogorsk and Tagil), made mainly by Middle Paleozoic volcanic strata and marine, often deep-sea sediments, as well as deep-seated igneous rocks (gabbroids, granitoids, less often alkaline intrusions) that break through them - i.e. n. greenstone belt of the Urals;
- Ural-Tobolsk anticlinorium with outcrops of older metamorphic rocks and wide development of granitoids;
- East Ural synclinorium, in many respects similar to Tagil-Magnitogorsk.

At the base of the first three zones, according to geophysical data, an ancient, Early Precambrian, basement is confidently traced, composed mainly of metamorphic and igneous rocks and formed as a result of several epochs of folding. The oldest, presumably Archean, rocks come to the surface in the Taratash ledge on the western slope of the Southern Urals. Pre-Ordovician rocks in the basement of the synclinories of the eastern slope of the Urals are unknown. It is assumed that the Paleozoic volcanic strata of synclinoria are based on thick plates of hypermafic and gabbroids, which in some places come to the surface in the massifs of the Platinum-bearing belt and other related belts; these plates, possibly, are outcasts of the ancient oceanic bed of the Ural geosyncline.

In the Late Carboniferous-Permian, sedimentation on the eastern slope of the Urals almost stopped and a folded mountain structure formed here; on the western slope at that time, the Cis-Ural marginal foredeep was formed, filled with a thick (up to 4-5 km) strata of detrital rocks that were carried down from the Urals - molasse. Triassic deposits have been preserved in a number of depressions-grabens, the occurrence of which in the north and east of the Urals was preceded by basalt (trap) magmatism. Younger strata of Mesozoic and Cenozoic platform deposits gently overlap folded structures along the periphery of the Urals.

A small absolute height determines the predominance of low-mountain and mid-mountain geomorphological landscapes in the Urals. The peaks of many ranges are flat, while some mountains are domed with more or less soft outlines of the slopes. In the Northern and Polar Urals, near the upper border of the forest and above it, where frosty weathering is vigorously manifested, stone seas (turmeric) are widespread. These places are also characterized by upland terraces resulting from solifluction processes and frost weathering.

Alpine landforms are extremely rare in the Ural Mountains. They are known only in the most elevated parts of the Polar and Subpolar Urals. The bulk of modern glaciers of the Urals are connected with the same mountain ranges.

"Lednichki" is not an accidental expression in relation to the glaciers of the Urals. Compared to the glaciers of the Alps and the Caucasus, the Urals look like dwarfs. All of them belong to the cirque and cirque-valley type and are located below the climatic snow boundary. The total number of glaciers in the Urals is 122, and the entire area of glaciation is only a little over 25 km2. Most of them are in the polar watershed part of the Urals between 670-680 s. sh. Caro-valley glaciers up to 1.5-2.2 km long have been found here. The second glacial region is located in the Subpolar Urals between 640 and 65°N. sh.

A remarkable feature of the Ural relief is the ancient leveling surfaces. They were first studied in detail by V. A. Varsanofyeva in 1932 in the Northern Urals and later by others in the Middle and Southern Urals. Various researchers in different places of the Urals count from one to seven leveled surfaces. These ancient leveling surfaces serve as convincing proof of the uneven uplift of the Urals in time. The highest of them corresponds to the most ancient cycle of peneplanation, falling on the lower Mesozoic, the youngest, lower surface is of Tertiary age.

Divya near Polyudova Ridge and Kapova on the right bank of the Belaya River.

The Ural Mountains are a treasure trove of various minerals. There are 48 types of minerals in the Ural Mountains.

In the relief of the Urals, two bands of foothills (western and eastern) and a system of mountain ranges located between them, elongated parallel to each other in a submeridional direction, are clearly distinguished, corresponding to the strike of tectonic zones. The ridges are separated from each other by extensive depressions along which rivers flow. As a rule, the ridges correspond to anticlinal folds, composed of older and more durable rocks, and depressions are synclinal.

Rice. one. Geological boundaries