The term aulacogen is derived from 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.
The
Southern Oklahoma Aulacogen is an
Eocambrian rift system formed as a product of intracontinental rifting during the breakup of
Pannotia. The Southern Oklahoma Aulacogen is located in southwestern
Oklahoma and extends into northeastern
Texas. The Southern Oklahoma Aulacogen is a failed rift zone that was active during the
Early Cambrian during the breakup of the
supercontinentRodinia and the opening of the
Iapetus Ocean. Volcanism and later faulting associated with the aulacogen created the
Wichita and
Arbuckle mountains. The rocks that were formed during active rifting of the aulacogen are now exposed in the Wichita and Arbuckle mountains through the processes of
uplift and
erosion. The majority of these rocks are made up of
basalts and other
mafic and
intermediate 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 the
Mississippi embayment and the
Southern Oklahoma Aulacogen were formed between 500-600 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.