Aulacogen

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An aulacogen is a failed arm of a triple junction. [1] Aulacogens are a part of plate tectonics where oceanic and continental crust is continuously being created, destroyed, and rearranged on the Earth’s surface. Specifically, aulacogens are a rift zone, where new crust is formed, that is no longer active. [2]

Contents

Origin of term

The term "aulacogen" is derived from the Greek aulax (furrow) and was suggested by the Soviet geologist Nikolay Shatsky in 1946. [3] [4]

Formation

A triple junction is the point where three tectonic plates meet; the boundaries of these plates are characterized by divergence, causing a rift zone or spreading center; a transform fault; or convergence causing subduction or uplift of crust and forming mountains. The failed arm of a triple junction can be either a transform fault that has been flooded with magma, or more commonly, an inactive rift zone. [2] Aulacogen formation starts with the termination of an active rift zone, which leaves behind a graben-like formation. Over time, this formation starts to subside and eventually minor volcanism starts to take place. The final inversion stage takes place when tectonic stress on the aulacogen changes from tensional to compressional forming horsts. [1] The inversion of ancient, buried aulacogens can exert a dramatic effect on crustal deformation. [5]

Characteristics

Aulacogens can become a filled graben, or sedimentary basin surrounded by a series of normal faults. These can later become the pathway for large river systems such as the Mississippi River. [6] The rock forming an aulacogen is brittle and weak from when the rift zone was active, causing occasional volcanic or seismic activity. Because this is an area of weakness in the crust, aulacogens can become reactivated into a rift zone. [1] An example of a reactivated aulacogen is the East African Rift or the Ottawa-Bonnechere Graben in Ontario and Quebec, Canada, an ancient aulacogen that reactivated during the breakup of Pangaea. Abandoned rift basins that have been uplifted and exposed onshore, like the Lusitanian Basin, are important analogues of deep-sea basins located on conjugated margins of ancient rift axes.

Examples

Africa

Asia

Europe

North America


The Midwestern United States can attribute many of its features to failed rift zones. Rifting in this part of the continent took place in three stages: 1.1 billion years ago, 600 million years ago, and 200 million years ago. Both the aulacogen associated with the Mississippi embayment and the Southern Oklahoma Aulacogen were formed between 500-600 million years ago. [6] [12]

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References

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  2. 1 2 Robert, Christian M. (2008-01-01). "Chapter Seven Aulacogens". In Robert, Christian M. (ed.). Developments in Marine Geology. Global Sedimentology of the Ocean: An Interplay between Geodynamics and Paleoenvironment. 3. Elsevier. pp. 239–248. doi:10.1016/s1572-5480(08)00207-8. ISBN   9780444518170.
  3. Shatski, Nicholas S (1946). The Great Donets basin and the Wichita System; comparative tectonics of ancient platforms. Geology Series, No. 6. Akademiia Nauk SSSR Doklady. pp. 57–90.
  4. Burke, K (May 1977). "Aulacogens and Continental Breakup". Annual Review of Earth and Planetary Sciences. 5: 371–396. doi:10.1146/annurev.ea.05.050177.002103.
  5. Martins-Ferreira, M. A. C. (2019). Effects of initial rift inversion over fold-and-thrust development in a cratonic far-foreland setting. Tectonophysics, 757, 88-107.
  6. 1 2 Keller, G.R.; Lidiak, E.G.; Hinze, W.J.; Braile, L.W. (1983). The Role of Rifting in the Tectonic Development of the Midcontinent, U.S.A. Developments in Geotectonics. 19. pp. 391–412. doi:10.1016/B978-0-444-42198-2.50028-6. ISBN   9780444421982.
  7. 1 2 Biswas, S.K. (1999). "A Review on the Evolution of Rift Basins in India during Gondwana with special reference to Western Indian Basins and their Hydrocarbon Prospects" (PDF). PINSA. 65 (3): 261–283.
  8. Soares, D.M.; Alves, T.M.; Terrinha, P. (2012). "The breakup sequence and associated lithospheric breakup surface: Their significance in the context of rifted continental margins (West Iberia and Newfoundland margins, North Atlantic)". Earth and Planetary Science Letters. 355–356: 311–326. doi:10.1016/j.epsl.2012.08.036.
  9. 1 2 3 4 5 Park, R.G. (1988). Geological Structures and Moving Plates. Glasgow: Blackie. pp. 192–193. ISBN   978-0-216-92250-1.
  10. 1 2 3 4 5 Bally, A. W.; Bender, P. L.; McGetchin, T. R.; Walcott, R. I., eds. (1980). Dynamics of Plate Interiors (Geodynamics Series Volume 1). Washington, D.C.: American Geophysical Union. p. 56. ISBN   0-87590-508-0.
  11. Hanson, Richard E.; Puckett Jr., Robert E.; Keller, G. Randy; Brueseke, Matthew E.; Bulen, Casey L.; Mertzman, Stanley A.; Finegan, Shane A.; McCleery, David A. (2013-08-01). "Intraplate magmatism related to opening of the southern Iapetus Ocean: Cambrian Wichita igneous province in the Southern Oklahoma rift zone". Lithos. Large Igneous Provinces (LIPs) and Supercontinents. 174: 57–70. doi:10.1016/j.lithos.2012.06.003.
  12. Brueseke, Matthew E.; Hobbs, Jasper M.; Bulen, Casey L.; Mertzman, Stanley A.; Puckett, Robert E.; Walker, J. Douglas; Feldman, Josh (2016-09-01). "Cambrian intermediate-mafic magmatism along the Laurentian margin: Evidence for flood basalt volcanism from well cuttings in the Southern Oklahoma Aulacogen (U.S.A.)". Lithos . 260: 164–177. doi: 10.1016/j.lithos.2016.05.016 .