Tectonic structures. The oldest tectonic structures

Tectonic structures are large areas of the solid outer shell of the planet. They are limited to deep faults. The movements and structure of the cortex are studied within the framework of a discipline such as tectonics.

General information

Tectonic structures are studied using geographic mapping, geophysical methods (seismic prospecting, in particular), and drilling. The study of these sites is carried out in accordance with the accepted classification. Geology examines medium and small forms, about 10 km in cross section, tectonics - large formations, over 100 km. The first are called dislocations of various types (discontinuous, injective, etc.). The latter include synclinoria and anticlinoria in folded areas, avlakogeny, syneclise, anteclise within plates, shields, pericritorial subsidence. This category also includes the underwater passive and active margins of the continents, platforms, geosynclinal belts, oceans, orogens, mid-ocean ridges, rifts, etc. These most large-scale tectonic structures encompass the hard shell and the 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 entire geological stage of the history of the planet. Global tectonic structures are those 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

On the basis of unity of movement, comparative monolithicity, lithospheric plates are distinguished . To date, there are 7 major and 11-13 smaller sites. The former include the Eurasian, North- and South-American, African, Indo-Australian, Pacific, Antarctic tectonic structures. To smaller formations include the Philippine, Arabian, Caribbean plates, Coconut, Nasca, etc.

Fractures

These tectonic structures separate the lithospheric plates. Among them, first of all, rifts are singled out. 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 faulty formations are the transform regions that cut the rifts perpendicularly. On their lines there is a horizontal shift of sections of lithospheric plates adjacent to them.

Platforms

They are slow-moving rigid blocks of the cortex. These sites have passed a fairly long stage of development. Platforms are three-tiered. In their structure there is a crystalline basement, which is formed by basalt and granite-gneiss layers. In the platforms there is also a sedimentary cover. The crystalline basement is formed by layers of metamorphic rocks wrinkled into folds. All this difficultly dislocated thickness is broken by intrusions (most of them having an average and acid composition). Depending on the age of the foundation, the platforms are divided into young and ancient tectonic structures. The latter act as the core of the continents, occupying their central part. The younger formations are located on their periphery. The sedimentary cover contains mainly non-dislocated beds of lagoon, shelf and, in rare cases, continental sediments.

Shields and plates

These types of tectonic structures are distinguished by the specifics of the geological structure. A shield is a section of the platform on which the crystalline basement is located on the surface, that is, there is no sedimentary layer in them. In the relief, shields are represented, as a rule, by plateaus and elevations. Plates are platforms or their parts, characterized by a powerful sedimentary layer. Their formation is conditioned by tectonic immersion and sea transgression. In the relief, slabs usually correspond to elevations and lowlands.

Anteclise

They represent the largest positive formations of slab sites. The surface of the foundations is convex. The saddle cover is not very powerful. Formation of anteclise is due to tectonic uplift of the territory. In this connection, many horizons present in neighboring negative areas may not appear in them.

Arrays and protrusions

They are regional structures of anteclise. Arrays are represented by their higher parts. In them, the foundation is either at the surface or overlapped by sedimentary formations of the Quaternary age. Speaks are called parts of arrays. They are represented by elongated or isometric uplifts of the basement, reaching a diameter of 100 km. There are also buried protrusions. Above them, the sedimentary cover is represented in the form of a strongly reduced section.

Syneclise

They are the negative largest super-regional structures of plate formations. The surface of their basement is concave. They are distinguished by a flat bottom, and also very flat angles of incidence of layers on the slopes. Syneclises are formed during tectonic immersion of the territory. In this regard, their sedimentary cover is characterized by high power.

Monoclines

These tectonic structures are distinguished by a one-sided inclination of the strata. Their angle of incidence rarely exceeds 1 degree. Depending on the rank of the negative and positive structures, between the boundaries of which the monocline is located, its category may also be different. From the regional formations of the sedimentary cover, grabens, horsts, and saddles are of interest. The latter occupy an intermediate position along the height of the surface. Saddles are located above the negative structures surrounding them, but below the positive ones.

Folded areas

They are characterized by a sharp increase in the thickness of the cortex. Mountain-folded areas are formed when the lithospheric regions converge. Most of them, especially young, are characterized by high seismicity. The age of the formations is the basic principle of classification of mountain-folded areas. It is installed by the youngest crumpled strata. Mountain ranges are divided, therefore, into:

1. The Baikal.
2. Hercynian.
3. Caledonian.
4. Alpine.
5. Cimmerian.

This classification is considered rather conditional, since most scientists recognize the continuity of folding.

Folding-block blocks

These formations are formed due to the revitalization of horizontal and vertical tectonic movements within the boundaries of previously arisen and often already destroyed systems. In this regard, the folded-block structure is more characteristic for the Paleozoic and earlier stages. The relief of the massifs, in general, is similar to the configuration of the rock formations. However, this does not always appear in folded-block areas. For example, in young mountains anticlinor structures correspond to ridges, and synclinoriums correspond to intermountain troughs. Inside the folded sections, as well as on their periphery, respectively, marginal and advanced valleys and valleys are distinguished. On the surface of these formations are coarse clastic products, arising from the destruction of mountain formations - Molasses. Formation of piedmont troughs is the result of subduction of lithospheric sites.

Central Russia

Each large natural complex is represented as a single geostructural area of a large area. This can be a platform or fold system of a particular geological age. Each formation has an appropriate expression in the relief. All of them differ in their climatic conditions, in the features of soil and vegetation cover. The tectonic structure of the Urals is of primary interest. In the modern state, it is a meganticlinorium, which consists of several anticlinoria, elongated meridionally and separated by synclinoria. The latter correspond to the longitudinal valleys, the first to the ridges. The key Urtalt anticlinorium passes through all education. By the composition of the Riphean deposits, it can be concluded that during the period of their accumulation an intensive subsidence occurred. At the same time he was repeatedly replaced by short-term uplifts. By the end of the Riphean Baikalian folding arose . The uplifts began to increase 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 of Baikal folding. As a result, areas were formed that differed from those that arose at a later time. They continue to form the foundation of the Timan-Pechora margin in the East European Platform.

Siberian tectonic structure: Aldan Highlands

The formations on this territory are composed of prehistoric gneisses and Proterozoic schists. They belong to the Precambrian Siberian Platform. It is necessary, however, to say about certain features that the tectonic structure possesses. The Aldan Highlands developed throughout the Meso-Cenozoic history between the southern northern Baikal areas and the platform. At many sites the rocks of the crystalline basement are at the surface. They are represented by fine-grained granites, ancient quartzites, marbles and gneisses. On the northern slope there is an area, the foundation of which lies at a depth of about 1.5 km. Its rocks are broken by granite intrusions at different stages of geological development.

European part

The mountains of Khibiny are of interest here. The tectonic structure is represented by denuded dismembered 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. They predetermined the terrain. The alkaline massif of the territory is represented by one of the multiphase complex intrusions. It is located on the boundary of the Gneiss Archaean complex and the Proterozoic formations of the Varzuga-Imandra formation, as well as in the zone of the key transverse fault that runs along the r. Cola - r. The Niva.