Geosyncline originally called a geosynclinal is an obsolete geological concept to explain orogens which was developed in the late 19th and early 20th centuries before the theory of plate tectonics was envisaged. A geosyncline was described as a giant downward fold in Earth's crust with associated upward folds (geanticlines, geanticlinals) that preceded the climax phase of orogenic deformation. The theory served as a means to explain the formation of mountains.
The geosyncline concept was first developed by the American geologists James Hall and James Dwight Dana in the mid-19th century during the classic studies of the Appalachian Mountains. Émile Haug actualized the geosyncline concept and "reintroduced" it to Europe with a 1900 publication. Eduard Suess, a leading geologist of his time, disapproved the concept of geosyncline and argued in 1909 against its use due to its associated theories. This did not stop further development of the concept by Leopold Kober and Hans Stille in the first half of the 20th century, both of whom worked on a contracting Earth framework. Stille and Kober had rather similar views.
The development of the geosycline concept in the aftermath of Eduard Suess' book Das Antlitz der Erde (1883–1909) by Stille and Kober was not unchallenged as another school of thought was led by Alfred Wegener and Émile Argand. This competing view rejected Earth contraction and argued for continental drift. These two views can be called fixist in the case of geosyncline theory and mobilist for the support of continental drift.
Marshall Kay adapted the geosyncline concept to plate tectonics in 1951 as did John F.Dewey and John M.Bird in 1970. The term continued to have usage within a plate tectonics framework in the 1980s, albeit Celâl Şengör argued in 1982 against its use considering its association to pre-plate tectonics ideas.
Most modern geologists regard the concept as obsolete and largely explain the development of linear troughs in terms of plate tectonics; the term geosyncline, however, remains in use.
As a geosyncline depression originated uplifted geanticlines were eroded providing sediments that filled the basin. According to Stille geosynclines formed as depressions without any faulting and if faults were found these were the product of later processes like the final collapse of the geosyncline. Collapse of geosynclines into orogens were thought by Dana and Stille to be the result of Earth's contraction over time. In Stille's and Kober views geosynclines were together with orogens the unstable parts of Earth's crust in stark contrast with the very stable Kratogens. In Stille's held geosynclines developed as result of contractional forces that also formed epeirogenic uplifts resulting in a pattern of undulation of Earth's crust. While this was according to him the common state of Earth episodic worldwide revolutions collapsed geosynclines into orogens.
Steinmann interpreted ophiolites using the geosyncline concept. He theorized that the apparent lack of ophiolites in the Peruvian Andes was either indebted to the Andes being preceded by a shallow geosyncline or the Andes representing just the margin of a geosyncline. Thus, Steinmann added this to a distinction between Cordilleran-type and Alpine-type mountains. According to Stille a type of geosyncline called eugesynclines were characterized by producing an "initial magmatism" that in some cases corresponded to ophiolitic magmatism.
Regarding oceans Kober held them to be strictly different to geosynclines. Kober further held that mid-ocean ridges were orogens, while Stille disagreed showing that they, as seen in Iceland, were places of extensional tectonics. Argand on the other side argued that geosynclines that stretched enough could turn into oceans basins as a material called sima surfaced.
|Geosyncline type||Geosyncline subtype||Initial magmatism||Resulting mountain type|
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The major mountain-building idea that was supported from the 19th century and into the 20th is the geosynclinal theory.
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- Şengör, A.M.C.; Natal'in, B.A. (2004). "Phanerozoic Analogues of Archean Oceanic Basement Fragments". In Kusky, T.M. (ed.). Precambrian Ophiolites and Related Rocks. Developments in Precambrian Geology. 13. ISBN 0-444-50923-2.