In the molten mantle of our planet, various geochemical processes, called endogenous, are constantly taking place. Such processes are caused by the thermal energy of the mantle and the earth's crust. Energy sources are the decay of radioactive elements and the gravitational differentiation of mantle rocks. These processes cause phenomena such as earthquakes, the appearance and development of islands, ocean depressions and mountain ranges, volcanic eruptions, rock metamorphism, deformation and tectonic movements of the earth's crust in the vertical and lateral planes.
Earth's crust tectonics
The tectonic movements of the earth's crust are characterized by great complexity and have various forms. In the course of geological history, the layers of the earth's crust were compressed into folds, pushed against each other, lowered, broken apart under the influence of tensile, compression, or friction forces.
In geology, the process of lifting the earth's crust is called diastrophism and is divided into orogenesis - mountain building, and epeirogenesis - the formation of continents.
Epheirogenic movements are characterized by slow secular movements with a small (on a geological scale) amplitude, do not lead to the formation of folds, discharges, and other disturbances. On the scale of the geological history of the planet, they can be called oscillatory.
Orogenic movements lead to the formation of mountain ranges. Compression of the continental crust during the collision of lithospheric plates forms folded mountains.
Forms of folded bedding of rocks
A fold is a wave-like bend of a rock formation while maintaining its integrity. The elementary forms of folds are synclinal (concave) and anticlinal (convex) forms of folds. In undisturbed geological structures, they are usually located nearby and are called full folds.
Syncline
The synclinal is a fold in which parallel strata of previously horizontally occurring rocks sink to the center. The youngest rocks, which at the beginning of the deformation were the upper layer of sedimentary rocks, are located along the axis of the fold, and the oldest - on its wings.
In severely deformed rocks, when it is impossible to determine the roof and the bottom of the formation, this term - “synclinal” - is not used, it is replaced with the word “synform”.
A bowl is a syncline, the length of which is almost equal to the width, has a rounded shape.
Mulda is a syncline, which has a horizontal projection of an oval shape.
Anticlinal fold
In the anticline, the layers horizontally lying before the formation of folding rise in the center of the fold. The rocks, which at the beginning of the deformation were the uppermost layer of sedimentary rocks, are located on the wings of the fold, and the oldest - along its axis.
By analogy with the syncline, if it is impossible to determine the age of the rocks that make up the fold, the name "anticline" is not used. In this case, the fold of the rocks, convex upward, is called the antiform.
An anticlinal fold with comparable length and width is called a dome.
Monocline
Unlike the syncline and anticline, the monocline is not a folded structure, despite the similar sound. Monoclinal bedding of layers is formed when one plate of the earth's crust creeps onto another along the fault line and is characterized by the same, very close to the horizon line, slope of the rock formations. Sometimes it is considered as a very large fold with one wing.
In monoclines, knee-like bends of the beds in the vertical plane are often found without violating their integrity, but with stretching of the layers. Such bends are called flexures.