The platform in geography is a large section of the continental crust, characterized by a relatively calm tectonic regime. Platforms arise in areas formed during the closure of geosynclinal systems, through their successive transformation into stable tectonic sections. It is known that platforms in geography are part of lithospheric plates. They consist of lower and upper tiers. Below is the foundation, or plate. According to the time of formation, they are divided into young and ancient.
Platform structure
In geography, the platform is the foundation of the earth’s crust about fifty kilometers thick. These formations are divided into two parts: the lower floor is located below, that is, the foundation of the platform, and at the top is the platform cover, or the upper, young layer. Between these layers there is a border called the intermediate structural layer. In different areas, it has a different thickness. Platforms themselves may not have a platform cover.
Types of platforms
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 floor. This species occupies about six percent of the entire continent. 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 different orders. The first order zones include:
- Shields.
- Plates.
- Lumps.
- Zones of pericraton subsidence.
And what is a platform in second-order geography, what types are referred to them? This group includes:
- Anteclises.
- Syneclises.
- Avlacogens.
Shields are a large area of the platform foundation. This type of formation is characteristic of ancient platforms. Those parts that relatively recently formed from under the foundation cover are called lumps.
Another structural element of the platform is the stove. It represents 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 not platforms, but plates. 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 on the edge of the platforms.
Anteclises and syneclises are structural elements of the second order. The first 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 inside plates or on shields.
Developmental stages
In the formation of platforms there are four stages of development.
- Kratonization is characterized by a predominance of uplifts and a rather strong final base. The stratification of gabbro-anorthosite pluton and rapakivi granite is characteristic of this stage.
- The second stage is aulacogenic. Most clearly manifested on the ancient platforms of the northern regions.
- The third stage is the slab. On ancient platforms, this stage covers the entire Phanerozoic and Jurassic Mesozoic periods. This stage ends with a phase of tectonic-magmatic activation. It is during these periods that magmatites characteristic of the platforms are formed.
- The fourth stage is epiplatform orogens.
First platforms
And what is a platform in geography and 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 were found on large areas.
East European platform
This platform covers the entire European part of Russia, Crimea, the Caucasus, part of Poland, Germany, some countries of the Scandinavian Peninsula. On the East European platform, Ukrainian and Baltic shields are distinguished, between which there is a huge Russian plate.
The Baltic shield 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 rocks of the Kola complex, preserved in a small area.
There are other complexes, but they are less than years old. These are the Nizhnekarelsky, Verkhnekarelsky, Belomorsky and Yatuli complexes. These species are formed by different sedimentary rocks: sandstones, crystals, schists, and siliceous formations. The power of these complexes can be different and reach two thousand meters. Volcanic rocks are rare. All these complexes have different ages - approximately 2500-1600 Ma. Scientists believe that it was during this period of time that the upper cover of the East European platform was formed.