What is the platform of the earth made of? What is called a platform and what is its structure. Structure, tasks of geology, its role in the construction industry

Platforms of the lithosphere

Platforms are relatively stable areas of the earth's crust. They arise on the site of previously existing highly mobile folded structures, formed during the closure of geosynclinal systems, by their successive transformation into tectonically stable areas.

A characteristic feature of the structure of all lithospheric platforms of the Earth is their structure of two tiers or floors.

The lower structural floor is also called the foundation. The foundation is composed of highly deformed metamorphosed and granitized rocks, penetrated by intrusions and tectonic faults.

According to the time of formation of the foundation, the platforms are divided into ancient and young.

The ancient platforms, which also make up the core of modern continents and are called cratons, are of Precambrian age and formed mainly by the beginning of the Late Proterozoic. Ancient platforms are divided into 3 types: Laurasian, Gondwana and transitional.

The first type includes the North American (Lawrence), East European and Siberian (Angaris) platforms, formed as a result of the breakup of the supercontinent Laurasia, which in turn was formed after the breakup of the Pangea protocontinent.

To the second: South American, African-Arabian, Hindustan, Australian and Antarctic. The Antarctic platform before the Paleozoic era was divided into the Western and Eastern platforms, which united only in the Paleozoic era. The African platform in the Archaean was divided into the Congo (Zaire), Kalahari (South African), Somalia (East African), Madagascar, Arabia, Sudan, and Sahara protoplatforms. After the collapse of the Pangea supercontinent, the African protoplatforms, with the exception of Arabian and Madagascar, united. The final unification took place in the Paleozoic era, when the African platform turned into the African-Arabian platform as part of Gondwana.

The third intermediate type includes small platforms: Sino-Korean (Huanhe) and South China (Yangtze), which at different times were both part of Laurasia and Gondwana.

Fig.2 Platforms and geosynclinal belts of the lithosphere

Archean and Early Proterozoic formations participate in the foundation of ancient platforms. Within the South American and African platforms, some formations belong to the Upper Proterozoic time. The formations are deeply metamorphosed (amphibolite and granulite facies of metamorphism); the main role among them is played by gneisses and crystalline schists, granites are widespread. Therefore, such a foundation is called granite-gneiss or crystalline.

Young platforms formed in the Paleozoic or Late Cambrian time, they border the ancient platforms. Their area is only 5% of the total area of ​​the continents. The foundations of the platforms are composed of Phanerozoic sedimentary-volcanic rocks that experienced weak (greenschist facies) or even only initial metamorphism. There are blocks of more deeply metamorphosed ancient, Precambrian rocks. Granites and other intrusive formations, among which ophiolite belts should be noted, play a subordinate role in the composition. In contrast to the foundation of ancient platforms, the foundation of young ones is called folded.

Depending on the time of completion of the basement deformations, the division of young platforms into Epibaikalian (the most ancient), Epicaledonian and Epihercynian.

The first type includes the Timan-Pechora and Mysian platforms of European Russia.

The second type includes the West Siberian and East Australian platforms.

To the third: the Ural-Siberian, Central Asian and Ciscaucasian platforms.

Between the basement and the sedimentary cover of young platforms, an intermediate layer is often distinguished, which includes formations of two types: sedimentary, molasse or molasse-volcanic filling of intermountain depressions of the last orogenic stage in the development of the mobile belt that preceded the formation of the platform; detrital and detrital-volcanic filling of grabens formed at the stage of transition from the orogenic stage to the early platform

The upper structural stage or platform cover is composed of non-metamorphosed sedimentary rocks: carbonate and shallow sandy-clayey in platform seas; lacustrine, alluvial and bog in a humid climate on the site of the former seas; eolian and lagoonal in arid climate. The rocks occur horizontally with erosion and unconformity at the base. The thickness of the sedimentary cover is usually 2-4 km.

In a number of places, the sedimentary layer is absent as a result of uplift or erosion, and the foundation comes to the surface. Such sections of platforms are called shields. On the territory of Russia, the Baltic, Aldan and Anabar shields are known. Within the shields of ancient platforms, three complexes of rocks of the Archean and Lower Proterozoic age are distinguished:

Greenstone belts, represented by thick sequences of regularly alternating rocks from ultrabasic and basic volcanics (from basalts and andesites to dacites and rhyolites) to granites. Their length is up to 1000 km with a width of up to 200 km.

Complexes of ortho- and para-gneisses, which, in combination with granite massifs, form fields of granite-gneisses. Gneisses correspond in composition to granites and have a gneiss-like texture.

Granulite (granulite-gneiss) belts, which are metamorphic rocks formed under conditions of medium pressure and high temperatures (750-1000 ° C) and containing quartz, feldspar and garnet.

Areas where the foundation is covered everywhere by a thick sedimentary cover are called slabs. Most of the young platforms are sometimes referred to simply as slabs for this reason.

The largest elements of the platforms are syneclises: vast depressions or troughs with slope angles of only a few minutes, which correspond to the first meters per kilometer of movement. As an example, we can name the Moscow syneclise with its center near the city of the same name and the Caspian syneclise within the Caspian lowland. In contrast to syneclises, large platform uplifts are called anteclises. On the European territory of Russia, the Belarusian, Voronezh and Volga-Ural anteclises are known.

Grabens or aulacogens are also large negative elements of the platforms: narrow, extended sections, linearly oriented and limited by deep faults. There are simple and complex. In the latter case, along with deflections, they include uplifts - horsts. Effusive and intrusive magmatism is developed along the aulacogenes, which is associated with the formation of volcanic covers and explosion pipes. All igneous rocks within the platforms are called traps.

Smaller elements are shafts, domes, etc.

Lithospheric platforms experience vertical oscillatory movements: they rise or fall. Such movements are associated with the transgressions and regressions of the sea that have repeatedly occurred throughout the entire geological history of the Earth.

In Central Asia, the formation of the mountain belts of Central Asia: Tien Shan, Altai, Sayan, etc. is associated with the latest tectonic movements of the platforms. Such mountains are called revived (epiplatforms or epiplatform orogenic belts or secondary orogens). They are formed during orrogenesis epochs in areas adjacent to geosynclinal belts.

The platform is a relatively stable block of continental crust. Platforms are vast sedentary areas of the earth's crust - the most stable blocks that create its solid frame. The structure of the platforms over most of their area is characterized by a two-tier structure: at the base lies an intensely deformed, metamorphosed and granitized basement, unconformably overlain by a sedimentary, in places with the participation of volcanic covers, cover that occurs subhorizontally and is not affected by metamorphism. The platform has a powerful foundation of folded-metamorphosed rocks, cut through by numerous intrusions and covered with sedimentary rocks of different thickness - a cover or upper tier. The sedimentary cover covers deep depressions of the lower stage (syneclise) up to 2-6 km deep. and anteclises approaching almost to the surface. It consists of horizontally lying or crumpled into gentle folds by subsequent tectonic movements already above the basement of layers of marine or continental origin. In places, the folded-metamorphic basement rises above the sedimentary cover in the form of shields (the Baltic Shield on the East European Platform). Thus, crystalline shields are distinguished within the platform, in which the ancient metamorphosed basement comes to the surface and areas where the basement is covered with a slightly deformed sedimentary cover. Such tectonic regions used to be called plates, but are now more commonly referred to simply as platforms.

Platforms with a Precambrian basement are called ancient; they make up, as it were, the cores of modern continents (except for Asia, in which 4 platforms are known) and are considered by many scientists as fragments of one continental mass "Pangea", formed by the middle of the Proterozoic (1700 million years). Platforms with a younger (Paleozoic - early Mesozoic) basement are known as young; they are located on the periphery of ancient platforms or fill the gaps between them (the West Siberian young platform between the ancient East European and Siberian ones).

14.1.3 1. What is a mineral? His structure. Classification

A mineral is a natural substance consisting of one element or a regular combination of elements, formed as a result of natural processes occurring in the depths of the earth's crust or on the surface. Each mineral has a specific structure and has its own physical and chemical characteristics. Currently, more than 2,500 minerals are known (not counting varieties). The science that studies minerals is called mineralogy.

Depending on the state of aggregation, minerals are divided into solid (quartz), liquid (mercury), gaseous (methane). The most widespread are solid minerals, among which, in turn, crystalline minerals predominate (the atoms in them are arranged in an orderly manner), and amorphous ones (with a chaotic arrangement of atoms) are much less common..

Most minerals have a certain chemical composition. Although the impurities included in them are capable of influencing the physical properties of minerals or even changing them, they are usually not mentioned in chemical formulas. When determining minerals, the shape of their crystals plays a very significant role. And although in the samples it is not always ideally expressed, but more often simply distorted, nevertheless, in most cases, it is possible to distinguish any signs of the crystalline structure - faces, shading, or constant angles between faces.

Typical forms of crystals are combined into seven crystallographic systems called syngonies. The distinction between them is made along the crystallographic axes and the angles at which these axes intersect.

There are the following crystallographic syngonies (systems): cubic (regular), tetragonal (square), hexagonal (hexagonal), trigonal (rhombohedral, or triangular), rhombic (sometimes called orthorhombic), monoclinic and triclinic.

The factors that determine the shape of a mineral are the structure of its crystal lattice and the packing of atoms, ions or molecules. If at the same chemical composition Since the atoms themselves are always identical, their mutual arrangement can differ significantly. The structure of the crystal lattice determines not only the shape of the crystals, but also their cleavage. So, for example, with a helical arrangement of particles in a lattice that does not allow flat interfaces to be held in it, the crystal does not split along cleavage (that is, it does not have cleavage)

End of work -

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Structure, tasks of geology, its role in the construction industry

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A platform in geography is a large area of ​​the continental crust, characterized by a relatively calm tectonic regime. Platforms arise in areas formed during the closure of geosynclinal systems by their successive transformation into tectonic areas of a stable type. It is known that platforms in geography are part of lithospheric plates. They consist of lower and upper tiers. Below is the foundation, or slab. According to the time of formation, they are divided into young and ancient.

Platform structure

In geography, a platform is the foundation of the earth's crust about fifty kilometers thick. These formations are divided into two parts: below is the lower floor, i.e. the foundation of the platform, and above is the cover of the platform, or the upper, young layer. Between these layers there is a boundary called the intermediate structural layer. In different areas, it has a different thickness. The platforms themselves may not have a platform cover.

Platform types

All earthly platforms are divided into young and ancient. The latter occupy about forty percent of the total area of ​​the continents. It is the ancient platforms that form the continents. Young platforms are characterized by the presence of a structural stage. This species occupies about six percent of the total area of ​​the continents. Young formations are located either between ancient lithospheric plates, or along their edge.

Structural elements

In geography, a platform is a formation that has certain structural elements of a different order. The zones of the first order include:

• Shields.
• Plates.
• Lumps.
• Zones of pericratonic subsidence.

And in second-order geography, which species are classified as such? This group includes:

• Anteclise.
• Syneclise.
• Aulacogens.

Shields are a large area of ​​platform foundation. This type of formation is typical for ancient platforms. Those parts that have relatively recently formed from under the foundation cover are called blocks.

Another structural element of the platform is the slab. It is an area of ​​continuous development of the platform (sedimentary) cover. Young platforms are most often covered with a sedimentary cover, which is why they are often called slabs rather than platforms. Examples of these are the Scythian, East Australian plates. Structural objects of the first order are represented by zones of pericratonic subsidence. These are plates, or deflections, the width of which is no more than three hundred kilometers. These elements are located along the edge of the platforms.

Anteclises and syneclises are structural elements of the second order. The former are large gentle uplifts within the plates. In these zones, the foundation lies at a depth of about one and a half kilometers. Syneclises are also large formations, but only depressions are located inside plates or on shields.

Stages of development

There are four stages of development in the formation of platforms.

• Cratonization is characterized by the predominance of uplifts and a rather strong final bottom. This stage is characterized by stratification of gabbro-anorthosite pluton and rapakivi granite.
• The second stage is aulacogenous. Most pronounced on ancient platforms northern regions.
• The third stage is slab. On ancient platforms, this stage covers the entire period of the Phanerozoic and Jurassic. This stage ends with a phase of tectonic-magmatic activation. It is during these periods that the magmatites characteristic of the platforms are formed.
• The fourth stage is epiplatform orogens.

First platforms

And in geography, what types of ancient formations are there? The most studied Precambrian types are East European and North American. Also worth noting are the Canadian and Baltic shields. In these places, ancient platforms have been found on large areas.

East European Platform

This platform covers the entire European part of Russia, the Crimea, the Caucasus, part of Poland, Germany, some countries of the Scandinavian Peninsula. On the East European platform, the Ukrainian and Baltic shields are distinguished, between which there is a huge Russian plate.

It occupies a large northwestern part. Karelia, the Kola Peninsula, Sweden and Finland are located on this territory. The ancient platform in some areas was formed three million years ago: these are the rocks of the Kola complex, preserved in a small area.

There are other complexes, but they less years. These are the Nizhnekarelsky, Verkhnekarelsky, Belomorsky and Yatuli complexes. These species are formed by different sedimentary rocks: sandstones, crystals, shales and siliceous formations. The thickness of these complexes can be different and reach two thousand meters. Occasionally there are volcanic rocks. All these complexes different age- approximately 2500-1600 million years. Scientists believe that it was during this period of time that the upper cover of the East European Platform was formed.