A triple junction is the point where threetectonic plates meet; the boundaries of these plates are characterized bydivergence, causing arift zone orspreading center; atransform fault; orconvergence causingsubduction oruplift of crust and forming mountains. The failed arm of a triple junction can be either a transform fault that has been flooded withmagma, or more commonly, an inactive rift zone.[2] Aulacogen formation starts with the termination of an active rift zone, which leaves behind agraben-like formation. Over time, this formation starts tosubside and eventually minorvolcanism starts to take place. The final inversion stage takes place whentectonic stress on the aulacogen changes fromtensional tocompressional forminghorsts.[1] The inversion of ancient, buried aulacogens can exert a dramatic effect on crustal deformation.[5]
Aulacogens can become a filled graben, orsedimentary basin surrounded by a series ofnormal faults. These can later become the pathway for large river systems such as theMississippi River.[6] The rock forming an aulacogen is brittle and weak from when the rift zone was active, causing occasional volcanic orseismic 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 theEast African Rift or theOttawa-Bonnechere Graben inOntario andQuebec,Canada, an ancient aulacogen that reactivated during the breakup ofPangaea. Abandoned rift basins that have been uplifted and exposed onshore, like theLusitanian Basin, are important analogues of deep-sea basins located on conjugated margins of ancient rift axes.
TheSouthern Oklahoma Aulacogen is anEocambrian rift system formed as a product of intracontinental rifting during the breakup ofPannotia. The Southern Oklahoma Aulacogen is located in southwesternOklahoma and extends into northeasternTexas. The Southern Oklahoma Aulacogen is a failed rift zone that was active during theEarly Cambrian during the breakup of thesupercontinentRodinia and the opening of theIapetus Ocean. Volcanism and later faulting associated with the aulacogen created theWichita andArbuckle mountains. The rocks that were formed during active rifting of the aulacogen are now exposed in the Wichita and Arbuckle mountains through the processes ofuplift anderosion. The majority of these rocks are made up ofbasalts and othermafic andintermediate lavas, which are typically associated with rift zones. An estimated 250,000 km3 of lava was erupted during active rifting.[11]
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 theMississippi embayment and theSouthern Oklahoma Aulacogen were formed between 500 and 600 million years ago.[6][12]
^abRobert, 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. Vol. 3. Elsevier. pp. 239–248.doi:10.1016/s1572-5480(08)00207-8.ISBN9780444518170.
^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.
^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.
^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.Bibcode:2013Litho.174...57H.doi:10.1016/j.lithos.2012.06.003.
