Geography: shields are ... Aldan shield. The Ukrainian Shield

The Earth's crust is heterogeneous and consists of different structural elements. The study of the structure of the lithosphere (the hard shell of the Earth) is among the tasks that geography science sets itself. Shields are one of such elements. They will be discussed in this article.

Earth's crust and its structure

The main structural elements of the earth's crust are lithospheric plates, which can be continental or oceanic. These two types differ in structure (cross section): in plates of the continental type, there is a granite layer.

The most stable (in the tectonic plan) parts of the Earth's lithospheric plates are called the platforms. At the same time, they are the nuclei (base) for the continents. In addition to them, orogenic (folded) belts are also distinguished within the lithospheric plates - epiplatform and epigeosynclinal belts.

The platform is the most stable structure of the earth's crust, which formed where hundreds of millions of years ago there were powerful mountain systems. Over time, they collapsed, and the surface at this place leveled off. So a powerful and stable structure is formed - the foundation. Subsequently, sedimentary rocks begin to accumulate on it, gradually creating a thick layer (cover).

All existing platforms on the Earth are divided into ancient (in the English-language literature they are often called cratons) and young. Below, the map shows the main (ancient) platforms of our planet. They are marked by a reddish tinge.

The structure of the earth's crust is studied by the science of geography (grade 7). Next, we will take a closer look at the structure of the platform.

The structural elements of the platform (geography, Grade 7)

The platform consists of two layers: a crystalline basement (lies below) and a sedimentary cover (covers the foundation).

In geological science, structures of four orders are distinguished, of which any platform consists. Shield, plate, anteclise and syneclise are the main ones. Next we will consider them. Acquaintance with these structures is quite enough for a full-fledged development of the school course "Geography".

Shields are the exits to the earth's surface of the crystalline basement of the platform. Dimensions of such outlets can reach 1000 or more kilometers in length. As a rule, shields are typical for ancient platform structures.

Plates are extensive sections of the platform, which are completely covered with a sedimentary cover. Very often young in age, the platform is covered with such a cover entirely. Therefore, they are also called slabs.

Anteclise and syneclise are already structures of the second order. Antekzeliy called gently raised sections of plates. The syneclise is a hollow cavity on the slab or, which is less common, within the crystalline shield.

In this article we will consider the shields of the ancient platforms of Eurasia - Siberian and East European. However, before this, we will dwell in more detail on the question "what is a shield".

Geography: shields are ...

The concept of "shield" is widely used in geological science. For the first time this term was used in Germany by Eduard Süss (in 1903).

The shield is an outcrop of the crystalline basement within the ancient platform. Thus, Precambrian rocks appear on the surface of the Earth, whose age can reach 3.5-4 billion years. They, as a rule, are represented by granites, quartzites, gneisses, which are exposed in fairly wide areas.

Features of the structure of shields

Shields are the main and most stable structures of the continents. As a rule, they are surrounded by belts, composed of rocks of the Cambrian age. In the relief, the shields are most often expressed by slightly convex plains or small elevations.

The shields are surrounded by more mobile and mobile zones, the processes of mountain building in which were recorded relatively recently (by geological standards - 100-200 million years ago).

The most famous examples of shields on our planet: Canadian, Ukrainian, Aldan, Baltic. These areas are confined to large deposits of ore minerals (iron ore, copper, manganese, gold, nickel, etc.). Thus, within the Aldan Shield, massive deposits of copper ores and apatites have been discovered. The largest in the world reserves of ferruginous quartzites (Krivoy Rog basin) are found on the Ukrainian Shield.

History of the formation and structure of the Siberian platform

The Siberian platform is a large geological area, occupying a huge area in the northeastern part of Eurasia. This is one of the oldest platforms on the planet, the foundation of which was formed in the archaean. After that, it was not once covered by the waters of the seas, as a result of which a powerful cover of sedimentary rocks was formed.

The Siberian platform has clear boundaries on the surface of the Earth: the northern one is the southern slopes of the Byrranga Mountains, the western slope is the Yenisei Valley, the southern boundary runs along the Stanovy Ridge, and the eastern boundary runs along the lower reaches of the Lena River.

The foundation of the Siberian platform is composed of rocks of the Archaean and Proterozoic ages, which are strongly crumpled. These are gneisses, amphibolites, slates, marble and others. Their age is quite solid: from 2.3 to 3.7 billion years. Sedimentary platform cover is composed of rocks of different ages. The northeastern extremity of the platform is characterized by intrusive rocks that form diamond tubes.

The Siberian platform is unusually rich in various mineral resources. There are large deposits of iron ore, mica, apatite, graphite. The sedimentary cover is associated with significant reserves of gas and oil, as well as coal, diamonds, copper, nickel ores and gold.

Geological structure of the Aldan Shield

The Aldan Shield is the protrusion of the crystalline basement within the Siberian Platform. It is localized in its southeastern part and coincides in the relief with the Aldan upland and the Stanovoi Ridge. In the south and west, the shield borders on the region of mountain building through a system of deep faults. In the northeast, it is covered by a thick cover of sedimentary deposits of Cambrian age.

On the sediments (floors) of the ancient foundation of the Aldan Shield, one can follow the evolution of the earth's crust as a whole. Thus, in the lowest tier there are gneisses, shales, marble and granulite quartzites. The next floor is filled with sedimentary-volcanogenic rocks, zoned metamorphosed. The upper floor is represented by powerful sediments of detrital and volcanogenic rocks, as well as large intrusions.

In different geological epochs, tectonic processes in the Aldan Shield have been intensified many times. This happened in the Paleozoic, Middle Mesozoic and Cenozoic. This is one of the distinguishing features of this crystal shield.

Deposits of many minerals are associated with the territory of the Aldan Shield. Thus, considerable reserves of iron and copper ores, mica, apatite, kimberlite, coal, gold, as well as various semi-precious stones have been discovered and explored here.

History of the formation and structure of the East European Platform

The Eastern European platform is one of the largest and most stable platforms of the modern earth's crust. It extends from the Scandinavian Peninsula to the Ural Mountains, occupying almost the whole of Northern and Eastern Europe.

In its structure there are two powerful outcrops of the crystalline basement - the Ukrainian and Baltic shields. Here on the surface in many places are the ancient rocks - mostly granites and quartzites. In places they form high cliffs, outcrops and very picturesque canyons. In the space between these shields, the Belorussian and Voronezh anteclises are located.

The basement of the platform is composed of magmatic and metamorphic rocks of Precambrian age, which are densely indented by deep tectonic faults. The Eastern European platform formed its foundation in the late Proterozoic. The platform cover consists of slightly deformed sedimentary and volcanic rocks of different geological ages.

The minerals of the East European Platform

Within the East-European platform, the richest deposits of various minerals have been explored. Some of them are associated with the foundation of this geological structure, others - with its sedimentary cover.

Large areas of iron ore (Kryvbas, Kursk Magnetic Anomaly, Kremenchug Basin and others), copper, titanium, nickel ores and apatites are confined to places of access to the basement of the platform. The sedimentary cover of the platform is associated with natural gas deposits (the Volgouralsk oil and gas province, the Dnieper-Donets basin and others), coal and brown coal (Donbass, Moscow region), phosphorites, bauxites and various building materials (limestone, marble, dolomites, etc.). .

Geological structure of the Ukrainian Shield

The Ukrainian crystal shield is the protrusion of the foundation of the East European platform on its southwestern outskirts. It stretches for a thousand kilometers (within Ukraine and partly from Belarus) from the Goryn River in the north to the shores of the Azov Sea in the south. On the map below it is marked in yellow.

The maximum width of the Ukrainian shield is 250 kilometers. The total area of its surface is about 135 thousand square kilometers.

The Ukrainian shield is composed mainly of magmatic and metamorphic rocks of the Archean age (gneisses, granites, amphibolites, migmatites and others). In many places these crystalline rocks are exposed, forming the most beautiful rocks, rapids and cascades on flat rivers.

Minerals of the Ukrainian Shield

To the protuberances of the foundations of ancient platforms, as is known, ore minerals are confined. And the Ukrainian shield here is no exception.

Within this geological structure, large deposits of iron ore (Krivoy Rog basin), uranium ores (Zheltovodskoye and Ternovskoye deposits), zirconium ores (Volnogorskoye deposit), precious and semiprecious stones, building materials (in particular in Zhytomyr and other regions of Ukraine, granite are mined Of the highest quality). In terms of the total mineral and resource potential, the Ukrainian Shield is practically unrivaled both in Europe and in the world.

There are also sedimentary-type minerals on this shield. Their deposits are confined to insignificant (no more than 50 meters) sections of the cover. First of all, it is the brown coal of the Dnieper basin, as well as the manganese ore of the Nikopol basin.

Conclusion

The study of the structure of the Earth's crust is part of the tasks that geography science sets itself. Shields are the structural elements of the ancient platforms of the Earth. As a rule, they are associated with powerful deposits of ore minerals and semiprecious stones.

The Aldan Shield, as well as the Ukrainian one, are the largest crystalline projections of the foundations on the continent of Eurasia. The first of them is located in Russia, within the Siberian platform, and the second - in Ukraine, on the East European platform.