Orogenesis

Etymology

The orogenesis term derives from the word “orogeny” (which is always a Synonyme), employed for the first time by Emile Littré in 1868. The contemporary terminology speaking about orogenesis appears in 1907 with Emile Haug. In Greek, oros indicates the Montagne: orogenesis thus studies the birth of the mountains . Actually, it includes also the study of the erosion and the disappearance of the reliefs, but it is true that the key question remained that of the formation of the mountains a long time, more than that of their origins or to become to them.

Historical elements

The first people having carried a glance Scientifique on the mountains were born at the 19th century. At that time, the study of planet is organized around systems as various as incompatible; but as regards its structure, the majority of the scholars integrate their work from the point of view of the “terrestrial revolutions” advanced by Georges Cuvier: taking into account the evolution alive, it is a question of discovering which necessary transformations caused upheavals likely to change gives it ecological on a total scale. One thus tries to connect knowledge in Zoologie and Botanique with the first observations purely Géologique S, like the layers and rock line of demarcation. Leonce Élie de Beaumont thus describes - without however indicating them by their modern name - the angular unconformities, i.e. the zones of contact between two layers of different nature and age and according to two also different geometrical plans.

If some people advance theories as for a Ground digs, the majority of the geologists of the 19th century are followers of the general theory of the Ground in cooling: the internal masses of planet losing their heat, they contract, which must cause the depression of the surface layers of what is already described like the terrestrial coat. However, everyone does not agree with this sight. Thus, Léopold de Buch is interested in another type of orogenesis, like successive and multiple risings. Some imagine, by observing the Volcan S, that the mountains are formed by craters of rising. All in all, the studies concentrate on the question of the movement, and forsake that of the age (for lack of means for of dating visible layers). This is why he is commonly admitted, and this since Rene Descartes, that the mountains of the same age are directed all in the same direction, i.e. there is unicity of the movement of depression or rising at a given time. Thus, the mountains are seen either as the frame of the Earth (De Beaumont proposes a geometrical system of orogeneses in redundant systems according to the geographical location), or like the result of a chaotic contraction.

The discordances described by Beaumont are explained better by James Hutton, which proposes a modern system in four phases (transformation into rock of the sediments; formation of in-depth molten masses; intrusion of these castings on the surface, therefore rising and swings; erosion, therefore updated of folds of different ages).

One can note the synthesis undertaken by Eduard Suess at the beginning of the 20th century, in his work Face of the ground . By noticing the prevalence of the alpine arcs, it gives up the idea of plain-direction and centres its study on the tensions animating the coat. The horizontal movements of the rocks were already studied by its predecessors, but never really put in relation to the radial movement (thus vertical in a given point of the coat) of the magma. In addition, the theory of the Plate tectonics progresses quickly, bringing its batch of questionings and new questions, but also of answers. While being based on this various work, Marcel Bertrand introduces in particular the decisive idea of Overthrust fold. Modern orogenesis is set up thus and benefits from technological advances of the beginning XXe, in the fields of the Datation, the Forage, the study of the seismic waves…

See too

orogenetic Cycle
Structure of the Earth
Geology

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