Geosyncline

As a geosyncline or Geosynkline a large bowl or a reduction in area of ​​the earth's crust is called. The term is part of the Geosynklinaltheorie, which is considered obsolete today. He was coined in the spelling Geosynclinale, 1873 by the U.S. geologist James Dwight Dana.

• 3.2.1 formation of geosynclines
• 3.2.2 convolution
• 3.2.3 uplift and erosion

Geosyncline

The term geosyncline is derived from the Greek συγκλίνειν ( synklinein ), which can be translated " tend to each other " with. The idea is that the two sides of a geosyncline have trough- shaped fold or another. In contrast to the syncline which refers to a portion of a geologic fold was Geosynklinale the entire deposition area of the later folded sediments.

The geosyncline was assumed to be elongated, stationary over long periods of subsidence zone of the earth's crust, which had at least the spatial extent of later arising from their mountains, served over a longer period than sedimentary basins and was later folded and lifted out.

The term geosyncline 'includes a word many of the geological structure and the rocks of mountains derivable contexts. It is therefore used partly for historical reasons and because of its brevity today, although the underlying Geosynklinaltheorie is considered outdated.

Differences are several types of geosynclines:

• Orthogeosynklinale: geosyncline with a strong reduction, usually several 100 km and 1000 km long, is folded into a Orogen Eugeosynklinale: core area of ​​a Orthogeosynklinale, deep marine, strong initial magmatism affected in the folding first, later in the interior of the resulting Mountains ( Interniden )
• Miogeosynklinale: exterior of a geosyncline, shallow marine, magmatism hardly present or absent, affiliated to the orogen after Eugeosynklinale, later on the front ( rarely also on the back ) of the resulting Mountains ( Externiden )

Other names of geosynclines were less common:

• Monogeosynkline: long and narrow, and over a long period of sinking marine space, separated from the ocean by a threshold
• Polygeosynkline: wide, articulated into several Teilgeosynklinalen, over a long period of sinking marine space, separated from the ocean by a threshold
• Mesogeosynkline: abyssal sea space between two continental blocks
• Parageosynkline: in contrast to Parageosynklinale a deep sea area at the edge of a continent, from the open ocean separated by chains of islands

Geoantiklinale

The counterpart of the geosyncline (also called Geantiklinale ) the Geoantiklinale, called the wide stretch of flat elevation areas. Since both were explained by bending of the earth's crust, they are interdependent. The Geoantiklinalen be changing frequently removed from exogenous ( external ) forces such as erosion, but the elevation seems so successful, however, is that the amount of stock remains. The detritus is poured into the geosyncline. A structure as in the geosyncline is not common here.

As Alpine geosyncline one called the Sea trough, in which the accumulated material that has been unfolded later to the Alps.

The Geosynklinaltheorie

The Geosynklinaltheorie was up to the paradigm shift in the geology in the 1960s, the significant tectonic model to explain the formation of mountains. In contrast to earlier orogeny theories they could without contradiction both the geological and geophysical knowledge of the era together and provide a timing of mountain building, so that they received wide recognition.

Based on the Hans Geosynklinaltheorie silence built around 1920 on his theory of Silence cycle, the categorized different mountain building phases. Only since the 1960s, sat down with new findings in the field of geology of the ocean floor, the currently prevailing theory of plate tectonics by. It explains the orogeny as a result of the collision of tectonic plates.

Basic assumptions

Geophysical assumptions

The Geosynklinaltheorie based on geophysical assumptions that corresponded to the level of knowledge of the 1870s and are now considered obsolete:

• The position of the continents and thus the oceans is unchangeable according to the Permanenztheorie. This was the first time in 1915 by Alfred Wegener doubted theory of continental drift, but was up in the 1960s as a reliable knowledge.
• After Beaumont's contraction theory, the earth's crust should pull together by slow cooling as the schrumpelnde surface of a dried apple and wrinkle. This mountain and ocean basins should arise. This theory had but after the discovery of radioactivity as an energy source inside the earth again be abandoned.

Geological observations

In addition, the theory were a number of geological observations based are still valid today:

• In mountainous rocks occur which have been formed on the seabed.
• Sediment pile reach a thickness of several kilometers. This is more than the usual depth of seas near continents.
• The rocks are folded and pushed over one another.
• Flysch and molasses were deposited over time by marine sediments and not fully involved in the folding.

The Geosynklinaltheorie was able to explain these observations in accordance with the geophysical assumptions. The necessary drive for the formation of geosynclines, the folding of the rocks and the elevation of the mountain was first explained by the contraction theory, after their elimination by Epirogenese. These are long -term and large-scale Erdkrustenverbiegungen, in which the storage conditions of the rocks are not significantly disturbed. The Geosynklinaltheorie remained consistent, were added to new knowledge of the geology of the ocean floor.

Orogeny after Geosynklinaltheorie

Formation of geosynclines

As the first stage of the orogeny the formation of a geosyncline was considered. Since the displacement of the tectonic plates and the possibility of formation and subduction of ocean floor were still unknown, the reduction in length of the earth's crust has been massively underestimated by the orogeny. The geosyncline was therefore assumed to be a relatively narrow, often elongated (up to well over 1000 miles), over long geological periods (more than 100 million years ) depth reduction zone. In it, the weathering and erosion debris adjacent mainlands ( uplifted Geoantiklinalen ) should accumulate by sedimentation. The flooding of the reduction zone by the sea could explain the occurrence of the ocean floor in the mountains, their steady lowering the thickness of marine sediments. Also intruding volcanic rocks could contribute to the replenishment of the geosyncline.

Convolution

Next stage of the orogeny, the folding of the sediments even in the depth and the formation of thrust faults was considered. The convolution was explained by that of the Geoantiklinalen in the geosynclines skidding material should not cause compressions, which could also explain the observed horizontal movements of plaice at least to a limited extent. In addition, the folding is first explained by the theory of the cooling of the earth. Simultaneously with the folding found the bed of flysch place in the geosyncline. The mountains should not or possibly peaking at this time in the form of some islands from the sea.

Uplift and erosion

Only after completion of the main phase of folding the uplift of the mountain range should be. Thus, a high land that is subject to erosion from the geosyncline. The detritus was deposited at the edge of the mountains as molasses, still partially folded and uplifted. This was later supplemented by silence as meaning that after raising the ablation continued until the formation of a craton. From a geomorphological point of view it created a peneplain.