Orogeny
The orogeny or orogenesis (composed of the Greek words ὄρος Oros mountain ' and γένεσις génesis, creation, conception, birth ' ) is caused by tectonic processes that are produced in many cases, directly by the shifting of tectonic plates. Special cases of the orogeny related to the formation of fracture Scholl mountains and broken fold mountains, which are not produced directly by the shift of tectonic plates.
A orogeny was formerly known as a time-limited process understood as only the fabric of the affected rocks were considered decisive operations. The investigation of active orogens such as the mountains on the Pacific coast of America shows that it is often temporally extensive and ongoing operations.
Mountain building processes
According to current understanding, the orogeny is due with a few exceptions, plate tectonic processes. The nature of the rock, its internal structure and the water content of the sediments involved influence the process, as external influences such as climatic factors and erosion processes. You alone decide what form a mountain range ( Orogen ), how high it is at a certain elevation rate, and how long its construction or its gradual leveling.
According to earlier notions of orogenesis is preceded by the formation of a so-called geosyncline: a large depression in which powerful layers of deep-sea sediments were deposited and the other before the reduction by large tectonic processes for a uplift area was. These rocks were later converted and partially moved hundreds of kilometers, so that they now find themselves in the mountains. By today's needs are met, the " geosyncline " the ocean or sea border situated in plate tectonic processes between the continental plates involved.
Collision of continental plates
The Earth's surface is made up according to the theory of plate tectonics from seven major and some minor lithospheric plates that move a few centimeters per year against each other. When two plates meet, so come to shear forces, which lead to a folding or stacking of crustal rocks. This results in a mountain range along the plate boundary. The Himalayas arose as by the impact of the Indian plate to the Asian plate. Around the same time, 30-50 million years ago, the folding of the Alps began by the collision of the Eurasian plate with a part of the African plate. These mountains are called collision Mountains.
Subduction of oceanic plates
If one continental plate on an oceanic plate so immerses the oceanic plate because of the higher density mostly in the mantle and becomes melted there again. This is known as subduction. In subduction zones often occur earthquakes and volcanic eruptions. Mountains are caused by heaped lava, but also by rising of lighter rock areas that have arisen during the subduction of the earth's core. The Andes are a result of the encounter of the Nazca plate with the South American plate. Further examples are the North American Cascade Range and the Japanese islands.
Autopsy of oceanic plates
In the collision of oceanic plates with others it does not come to a complete subduction of the oceanic crust in some cases. Parts of the oceanic plate will be abraded from its base camp and pushed onto the top plate ( autopsy ). Such body of rock are found in many mountain ranges, mostly as lenticular and less extensive deposits. The open-minded there are rocks called ophiolites and have a very characteristic form, which is clearly distinguishable from the surrounding rocks. In rare cases, larger parts of the oceanic crust are autopsied, such as in the Ophiolithkomplex of Oman.
The role of ablation in the orogeny
Even during the formation of a mountain range erosive forces are effective once the rock body rises above its surroundings. Here play physical factors (sunshine, thawing and refreezing of the rock ), chemical processes and mechanical factors (mainly by glaciers and running water) the decisive role. Depending on the uplift rate of a mountain range in relation to the removal rate will determine whether a mountain range continues to gain height or is removed faster. The principle is that higher mountains have higher corrosion rates, since the relief energy of a high mountain is higher than that of a low mountain range, and this in turn is higher than in the lowlands. The higher erosive effect of a rushing mountain stream compared to a Wiesenmäander in the plane is easy to imagine. The general rule is that the denudation, the areal ablation for example, by frost, a stronger effect than the line-like erosion of a river.
Simulations of mountain building processes showed that the ablation may can have a controlling influence on the course of mountain building. ,
Isostasy
Mountains are located to the underlying viscoplastic mantle in a kind of swimming equilibrium ( isostasy ). Here, the mountain block dive so deep into the mantle, that the mass of the displaced mantle rock corresponds to its own mass. This is similar to ships that are immersed in accordance with Archimedes' principle, the deeper the water, the heavier they are.
A mountain range extends approximately to the 5 - to 6 times its height above sea level into the mantle. Is removed by erosion at the surface rock, the mountain chain lifts so far are replaced to about 80 % of the removed rock mass. Although the tectonic upward movement has long since come to a standstill, to mountainous regions of years can hold at its peak level before the erosion prevails thus for many millions.
Phases of mountain building in the earth's
On Hans silence the division of geological career of Europe goes back into four main mountain building phases: the fennosarmatische, Caledonian, Variscan and Alpidic phase.
Almost all the "young" fold mountains of the world are in the last 20 to 40 million years ago, originated in the Alpine orogeny, the last of these phases. In this phase emerged, among other things, the High Atlas, the Pyrenees, the Alps and the Carpathians, the Dinarides, the mountain ranges of Turkey, the Zagros Mountains in Persia, the Himalayas and the western mountains of Burma, Thailand and Indonesia. In today's Alpine region the parent rocks were deposited in several marine areas; the marine sediments were then formed up to several kilometers thick and were folded in a complicated process whose main phase began about 70 million years ago, a mountain range. After the strongest uplift phase (before about 25 million years ago) the erosion afraid the spacious upscale area of tectonic zones of weakness through long and short valleys. The lifting of the Alps continues to this day ( with 1-3 mm per year), it will be offset by some equally strong erosion.
For historical reasons, the names of Hans silence are still used today, in part not only in Europe but also in other continents. In addition, there is a multiplicity of names for orogenies, which derive from the mountains of the region. Characteristic names usually more or less large-scale or as much of the earth's classified orogenies are listed in the following table.
Information in mya
Cretaceous, Cenozoic
Eurasia continent and subcontinent India
Mid- Paleozoic
Supercontinent Pangaea
Early Paleozoic
Old Great Continents Laurussia, Laurasia
Supercontinent Gondwana supercontinent Pannotia or
Mesoproterozoikum
Supercontinent Rodinia
Mesoproterozoikum
Merger of the continents Nena and Atlantica
Paleoproterozoic
Continents Nena, Atlantica, at the end supercontinent Columbia
Neoarchaikum, Paleoproterozoic
Small Continents Fennoscandia, Sarmatia, Volgo- URALIA, at the end supercontinent Kenorland? -
Supercontinent "First Earth"?