- Aulacogen
In
geology , an aulacogen is a failed arm of atriple junction of aplate tectonics rift system. A triple junction beneath a continental plate initiates a three way breakup of the continental plate. As the continental break-up develops one of the three spreading ridges typically fails or stops spreading. The resulting failed rift is called an aulacogen and becomes a filledgraben within the continent. However, the crust in an aulacogen region remains weakened by previous rifting activity and thus seismic activity and, occasionally, volcanic activity may re-occur subsequently from time to time.The
Mississippi embayment with the associatedNew Madrid Seismic Zone is an example of an ancient aulacogen that dates back to the breakup of the ancient continentRodinia . This ancient rift was the site of extreme earthquakes in the early 19th century in what is now the central U.S. TheRio Grande Rift is another example. On the Southwestern European margin (offshorePortugal ) is located another abandoned rift basin (Lusitanian Basin ) that evolved at the same time as the CanadianGrand Banks region, where theHibernia oil field is located. 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.As aulacogens remain places of weakness, given the appropriate conditions, they can reactivate into active rift valleys again, as had happened to the
Ottawa-Bonnechere Graben inOntario andQuebec ,Canada , an ancient aulacogen that reactivated during the breakup ofPangaea .The term "aulacogen" is derived from the Greek "aulax" (
furrow ) and was first applied as a geologic term by the Soviet geologistNicholas Shatski in 1946. [ [http://arjournals.annualreviews.org/doi/abs/10.1146/annurev.ea.05.050177.002103 Aulacogens and Continental Breakup] ]References
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