Tectonic structures are large areas of the planet’s solid outer shell. They are limited by deep faults. The movements and structure of the crust are studied in a discipline such as tectonics.
General information
Tectonic structures are investigated using geographic mapping, geophysical methods (seismic exploration, in particular), as well as drilling. The study of these sites is carried out in accordance with the accepted classification. Geology explores medium and small forms, about 10 km in cross section, tectonics - large formations, over 100 km. The former are called dislocations of various types (discontinuous, injective, etc.). The second group includes synclinoria and anticlinoria in folded areas, aulacogens, syneclises, anteclises within plates, shields, and pericratal lowerings. This category also includes underwater passive and active margins of the continents, platforms, geosynclinal belts, oceans, orogens, mid-ocean ridges, rifts, etc. These most large-scale tectonic structures cover the hard shell and lithosphere and are called deep.
Classification
Superglobal ancient tectonic structures reach tens of millions of square meters. km in area and thousands of kilometers in its length. They develop throughout the geological stage of the history of the planet. Global tectonic structures are formations that occupy up to 10 million square meters. km Their length reaches several thousand kilometers. The duration of their existence coincides with the previous sections. Subglobal tectonic structures of the earth's crust are also distinguished. They occupy an area of several million square meters. km and stretch for thousands of kilometers. The period of their development is more than 1 billion years.
Basic tectonic structures
Based on the unity of movement, comparative solidity, lithospheric plates are distinguished. To date, 7 largest and 11-13 smaller sites are known. The former include Eurasian, North and South American, African, Indo-Australian, Pacific, Antarctic tectonic structures. The smaller formations include the Philippine, Arabian, Caribbean plates, Coconut, Nazca, etc.
Fault formations
These tectonic structures separate lithospheric plates. Among them, rifts are primarily distinguished. They are divided into continental and mid-oceanic. The latter form a global system, the length of which is more than 64 thousand km. Examples of such sites are the East African (the largest on the planet), Baikal. Another type of fault formations are transform sections that cut rifts perpendicularly. Along their lines, a horizontal shift of the lithospheric plate sections adjacent to them occurs.
Platforms
They are sedentary rigid blocks of the cortex. These sites went through a rather long stage of development. The platforms are distinguished by a three-tier structure. Their structure contains a crystalline basement, which is formed by basalt and granite-gneiss layers. A sedimentary cover is also emitted on the platforms. The crystalline basement is formed by layers of metamorphic rocks crumpled into folds. Intrusion (mostly having an average and acidic composition) breaks through this complexly deployed stratum. Depending on the age of foundation formation, the platforms are divided into young and ancient tectonic structures. The latter act as the nuclei of the continents, occupying their central part. Younger formations are located on their periphery. The sedimentary cover contains predominantly undiluted layers of lagoon, shelf and, in rare cases, continental sediments.
Boards and plates
These types of tectonic structures are distinguished by the specificity of the geological structure. A shield is a section of the platform on which the crystalline basement is located on the surface, i.e. there is no sedimentary layer in them. In relief, shields are represented, as a rule, by plateaus and hills. Plates are platforms or their sections, characterized by a powerful sedimentary layer. Their formation is caused by tectonic immersion and marine transgression. In the relief, plate sections usually correspond to elevations and lowlands.
Anteclises
They represent the largest positive formations of plate sections. The surface of the foundations is convex. The sedimentary cover is not very powerful. The formation of anteclise is due to tectonic uplift of the territory. In this regard, many horizons present in neighboring negative areas may not be detected in them.
Arrays and ledges
They are regional structures of anteclises. Arrays are represented by their higher parts. In them, the foundation is either located near the surface or overlaps by sedimentary formations of the Quaternary age. The protrusions are called parts of arrays. They are represented by elongated or isometric elevations of the foundation, reaching a diameter of 100 km. Buried protrusions are also distinguished. Above them, the sedimentary cover is presented in the form of a greatly reduced section.
Syneclise
They are the negative largest superregional structures of plate formations. The surface of their foundation is concave. They have a flat bottom, as well as very gentle dip angles on the slopes. Syneclises form during tectonic immersion of the territory. In this regard, their sedimentary cover is characterized by high power.
Monoclines
These tectonic structures are characterized by one-sided inclination of the strata. Their angle of incidence rarely exceeds 1 degree. Depending on the rank of negative and positive structures, between the borders of which there is a monocline, its category can also be different. Of the regional formations of the sedimentary cover, grabens, horsts, and also saddles are of interest. The latter occupy an intermediate position along the height of the surface. The saddles are located above the negative structures surrounding them, but below the positive ones.
Fold areas
They are characterized by a sharp increase in the thickness of the cortex. Mountain-folded areas are formed during the convergence of lithospheric sites. Most of them, especially young ones, are characterized by high seismicity. The age of formations is the fundamental principle of classification of mountain-folded areas. It is installed on the youngest crumpled layers. Mountain ranges are thus divided into:
- Baikal.
- Hercynian.
- Caledonian.
- Alpine.
- Cimmerian.
This classification is considered rather conditional, since most scientists recognize the continuity of folding.
Block and block massifs
These formations are formed as a result of the revival of horizontal and vertical tectonic movements within the boundaries of previously arisen and often already destroyed systems. In this regard, a folded-block structure is more characteristic of the regions of the Paleozoic and earlier stages. The relief of the massifs is, in general, similar to the configuration of the bends of rock formations. However, this is far from always revealed in the folded-block areas. For example, in young mountains, the ridges correspond to the structures of anticlinoria, and inter-mountain troughs correspond to synclinoria. Inside the folded sections, as well as on their periphery, the marginal and advanced depressions and valleys stand out, respectively. On the surface of these formations are located coarse clastic products arising from the destruction of mountain formations - molasses. The formation of foothill troughs is the result of subduction of lithospheric sites.
Central Territory of Russia
Each major natural complex is represented as a single geostructural area of a large area. It can be a platform or a folded system of a specific geological age. Each formation has a corresponding expression in relief. All of them differ in climatic conditions, especially in the land cover. Of interest is primarily the tectonic structure of the Urals. In its current state, it is a meganticlinorium, which consists of several anticlinoria elongated meridionally and separated by synclinoria. The latter correspond to longitudinal valleys, the former to ridges. The key Uraltau anticlinorium passes through all education. According to the composition of the Riphean deposits, it can be concluded that during their accumulation, intensive lowering occurred. At the same time, he was repeatedly replaced by short-term uplifts. By the end of the Riphean, Baikal folding arose . The ups began, intensifying in the Cambrian. During this period, almost the entire territory turned into land. This is indicated by the very limited distribution of sediments, which are represented by green shales of the Lower Cambrian formation, marbles and quartzites. The tectonic structure of the Urals in the lower tier, thus, completed its formation with the Baikal folding. As a result of it, sites were formed that differ from those that arose at a later time. They continue to form the foundation of the Timan-Pechora outskirts within the East European platform.
Siberian Tectonic Structure: Aldan Highlands
Formations in this territory are composed of prehistoric gneisses and Proterozoic schists. They belong to the Precambrian Siberian platform. It is necessary, however, to say about some of the features that the tectonic structure possesses. The Aldan Highlands developed throughout the Meso-Cenozoic history between the southern northern Baikal sections and the platform. In many areas, the rocks of the crystalline basement are at the surface. They are represented by fine-grained granites, ancient quartzites, marbles and gneisses. There is an area on the northern slope, the foundation of which lies at a depth of about 1.5 km. Its rocks are broken through by granite intrusions at different stages of geological development.
European part
The Khibiny Mountains are of interest here . The tectonic structure is represented by denudation dissected elevated plains. They occupy the territory of the Kola Peninsula and Karelia. The tectonic structure that formed the Khibiny Mountains arose in the form of intrusions and dislocations. It was they who determined the terrain. The alkaline massif of the territory is represented by one of the multiphase complex intrusions. It is located on the border of the Gneissky Archean complex and the Proterozoic formations of the Varzug-Imandra Formation, as well as in the zone of the key transverse fault, which runs along the line r. Cola - p. Niva.