You cratons they are Earth's geological structures formed hundreds of thousands of years ago and present in areas of tectonic stability. These structures have two classifications, known as crystalline shields and sedimentary basins. They they form through two processes: sedimentation and rock erosion. In Brazil, both structures are found, as it is a geological structure without volcanic activity, that is, with tectonic stability.
Read too: Difference between weathering and erosion
What are cratons?
the cratons are ancient geological structures, that is, they are terrestrial formations formed hundreds of thousands of years ago. They formed in the Pre-Cambrian Era, in the Proterozoic and Archeozoic. In general, these terrestrial structures are quite stable, without strong or intense geological activities, that is, without the occurrence of seismic activities - earthquakes – in addition to presenting rocks igneous/magmatic and metamorphic.
They are formed by two types of geological structures: crystalline shields (antique solids) and the
sedimentary basins (continental platforms). These surfaces have very great geological richness, as there is the presence of metallic minerals, such as:iron;
copper;
tin;
silver;
aluminum, etc.
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You crystal shields or old massifs are internal structures formed by crystalline rocks - fiery and metamorphics. Thus, rock outcropping can occur in the relief, that is, these rocks can be exposed to the naked eye in nature. Crystalline shields characterize the plateau areas.
already the sedimentary basins or continental shelves are more recent rock formations, from the Paleozoic, composed by sedimentary rocks, which, in turn, are formed from the deposition of sediments. These rocks are generally layered and are formed by regions of relative depressions.
Craton formation
The formation of cratons too varies with geological structure. In general, one is linked to erosive processes, formed from the erosion of other rocks, and the other occurs by the deposition of materials or sediments. Thus, it is clear that in cratons there is a greater predominance of action by external erosive agents, or exogenous, such as water and wind, as these agents contribute to the erosive process.
You crystalline shields are formed from erosion of magmatic or igneous rocks, for the most part. They are also constituted by the solidification of terrestrial magma, resulting from areas where volcanic activity occurs.
already the sedimentary basins are structures that form from the accumulation or deposition of sediments.. These sediments originate from ancient mountainous areas that have eroded, were eroded and deposited in areas where cratons occur.
See too: What is historical time and geological time?
Cratons in Brazil
In Brazil, the geological structure is divided into two classes, as we have already seen. They are the crystal shields and the sedimentary basins.
You shieldscrystalline are very old geological formations and comprise a total of approximately 36% of the territory of Brazil. Because they are quite old, they were formed in the Pre-Cambrian geological period, that is, more than 4 to 2.5 billion years ago. It was also during this period that non-metallic minerals such as granite and slate were formed. Then some metallic minerals were formed.
You metallic minerals they are used in our daily lives as raw material for various products, and are also sold. Are they:
iron;
gold;
lead;
copper;
tin;
silver;
bronze;
manganese etc.
In the case of sedimentary basins, they occupy about 64% of the Brazilian territory and were formed in the Paleozoic, that is, from about 570 to 290 million years ago. As they were formed by sediment deposition, it is common in these areas the presence of materials formed from organic matter, so they are found in sedimentary basins or Petroleum, coal and natural gas. These products are also extracted for daily use and as raw material for various products.
Also access: Endogenous relief transformation agents: what are they?
solved exercises
Question 1 - (Uespi) Note the geological structure sketched below.
In this sketch, the arrow is indicating the following structure:
A) sedimentary basin.
B) asymmetric folding.
C) fjord.
D) geological fault.
E) dome.
Resolution
Alternative A. In general, sedimentary basins characterize the depression areas. The block-diagram (image) denotes a geological formation linked to this form of relief.
Question 2 - (UEL) The geological structure of Brazil is composed of:
I. crystalline shields, very old, of rigid and resistant rocks that originated plateaus and some depressions, making up 1/3 of the national territory.
II. sedimentary basins composed of sedimentary rocks that originated the plains, sedimentary plateaus or depressions, occupying about 64% of the country's total.
III. modern folds that originated plateaus and mountainous reliefs, formed in the Tertiary, occupying about 30% of the national territory.
IV. recent crystalline shields, little eroded by erosive processes, which gave rise to the forms of relief in which the mountainous plateaus predominate throughout almost the entire territory national.
Check the correct alternative.
A) Only statements I and II are correct.
B) Only statements I and IV are correct.
C) Only statements III and IV are correct.
D) Only statements I, II and III are correct.
E) Only statements II, III and IV are correct.
Resolution
Alternative A. Both the crystalline shields and the sedimentary basins are ancient structures, linked to erosion and the formation of the Brazilian relief structure: plateaus, plains and depressions.
By Gustavo Henrique Mendonça
Geography teacher
