Earth\'s crust

The earth's crust is the surface and solid part material whose the Ground is made. It is the upper part of the Lithosphère (which constitutes the tectonic plates).

The limit between the earth's crust and the higher coat is the Discontinuité of Mohorovicic, or Moho .

Composition of the earth's crust

The majority of the Roche S constituting the earth's crust are Oxyde S; the Chlorine, the Sulfur and the Fluor are the only important exceptions and their total quantity in any rock seldom exceeds the 1%. F.W. Clarke calculated that 47% of the earth's crust are made of Oxygène present mainly in the form of oxides, whose principal ones are the oxides of Silicium, Aluminum, Fer, Calcium, Magnésium, Potassium and Sodium. The Silice is the constituent major one of the crust in the form of Pyroxénoïde S, the most common minerals of the magmatic rocks and metamorphic. After a synthesis based on the analysis of 1672 types of rocks, Clarke obtained the following percentages of composition in mass:

All the other components are present in very small quantity (total < 1%).

Structure

One distinguishes the continental Croûte (30% of terrestrial surface) from the oceanic Croûte (70% of terrestrial surface):

the continental crust form primarily the Continent S. Certaines parts can however be immersed under Mer S or Océan S, such as for example the continental shelf. The continental crust is thick from 15 to 80 km, with an average of 30 km. It has an average composition of granitic rock with dioritic (known as intermediary), of Densité 2,7 to 2,8. The major part probably makes up of Gneiss. The base of the crust presents platings of Gabbro, resulting from fusion partial and old of the higher coat.

the oceanic crust form primarily the bottom of the Océan S. It is much finer (5 to 7 km in general). Made of basaltic rocks and Gabbro, it is also denser (3g/cm ³).

One thought that the earth's crust was primarily granitic, and one thus named it " Sial " (Silicon - Aluminum), in opposition to the coat which one named " sima" (Silicon - Magnesium). Now, it is known that the crust of the ground does not have a homogeneous composition since the oceanic crust is originally different from the continental crust, and these names are obsolete.

It also should be known that the oldest rocks found coming from the continental crust go back to 3700 million years. In parallel, oldest coming from the oceanic crust go back to 220 million years.

Movements

The Plate tectonics makes it possible to understand that the crust is created on the level of the oceanic dorsals. This crust is resulting from a fusion partial of the higher coat under the oceanic wrinkles.

The lithospheric movements of the plates are the main cause of the great structural modifications affecting the earth's crust. The seisms and the volcanicity are the markers of this activity of the planet Ground. to see Plate tectonics, Not hot

See too

Be-X-old: Зямнаякара Map-bms: Kerak bumi Simple: Crust (geology) Zh-yue: 地殼

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