The earth's crust is the upper part of the lithosphere. If you look at it on the scale of our planet, then this part will look like a thin film. But even this thin shell is not well understood. However, scientists were able to establish that the crust has the smallest thickness under the oceans, seas.
The deepest wells drilled in the earth's crust, up to ten kilometers long. Such indicators do not allow scientists to find out a sufficient amount of information about its structure, structure. Information about the composition of the lithosphere was obtained only due to seismic location. Decoding of seismic waves made it possible to assess the density of the earth's layers and their composition.
Earth's crust
The thickness of the earth's crust is different in different parts of the planet. It is more above the continents than under the oceans. The thickness of the mainland is an average of 35 kilometers. Under mountain ranges, it is several times larger - it reaches 80 or more kilometers. But under the deepwater part of the earth's crust has the smallest thickness - up to 15 km.
Bark structure
In addition to differences in thickness, the continental and oceanic crusts have their own peculiarities in the structure. Mainland is represented by the following layers:
- lower basalt (about 15 km);
- medium granite (about 10 km);
- upper sedimentary, formed from the decay products of crystalline rocks (about 5 km).
In total, the thickness of the continental-type crust is 30–40 km.
Oceanic consists of the following layers:
- upper sedimentary depth up to one kilometer;
- medium with a little-known composition;
- lower basalt depth of about five kilometers.
In total, the thickness of the oceanic crust is about 15 kilometers.
Transition zone
There is a transitional zone between the continental and oceanic layers. On it is the displacement of the granite layer. The border is not always clearly defined. In some areas, there is a gradual transition from the earth's crust of the oceanic species to the continental. An example of this is the transition from the Far Eastern seas to the edges of lithospheric plates. At this point, the crust has the smallest thickness, but it does not have a granite layer, although the upper sedimentary is well developed. The total thickness of the crust is about 15 kilometers.
Ranges rise over the oceans for several kilometers, and their length reaches 80 thousand km. The ridges are separated by faults. Seismological activity is high in the ridge zones; volcanism processes are observed. Here, almost constantly, magma breaks out, spreading in different directions by lava underwater flows.
Transitional Areas
Between the places where the crust has the smallest thickness, and where it is thicker, there is a transition zone. There are several types:
- Vityazevsky. This type of transition zone is characterized by the absence of a pronounced island arc, a shallow depth of the trench, and weak seismicity.
- Mariana Transitional Area. It is clearly expressed as an underwater ridge. The depth of the gutter is large. In this transition zone, high seismological activity and volcanism are noted. The sediment layer is thin.
- Kuril type. It has a large isolation of sea basins, a suboceanic type of the earth's crust. This type of transition zone is characterized by areas with sub-continental crust, island arcs, often double. Volcanic processes, seismological activity at maximum. The gutters have great depth. In them, the thickness of the sedimentary layer changes upward.
- Japanese type. It is characterized by the merging together of island arcs of different ages. Areas of the earth's crust are traced that are similar in structure to the mainland type. Volcanism and seismic activity are quite powerful. The bottom of the basins has a powerful sedimentary layer.
The Mediterranean transitional type is distinguished, which is characterized by a strong similarity with the structure of the continental-type crust.
The structural feature of the bark
Within the oceanic one, another species is distinguished - rifting. It is found on the mid-ocean ridges. A distinctive feature of the structure of the earth's crust in these zones is that the sedimentary cover at the bottom is almost completely absent. In these areas, high seismic activity is observed.
Thus, in those places where the crust has the smallest thickness, there is an oceanic crust, where the maximum thickness is continental, and the zone between them is transitional. The riftogenous region is distinguished into a separate category.