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翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク Southern Oklahoma Aulacogen ： ウィキペディア英語版 Southern Oklahoma Aulacogen The Southern Oklahoma Aulacogen is a failed rift, or failed rift arm (aulacogen), of the triple junction that became the Iapetus Ocean spreading ridges. It is a significant geological feature in the Western and Southern United States. It formed sometime in the early to mid Cambrian Period and spans the Wichita Mountains, Anadarko Basin, and Hardeman Basin. The Southern Oklahoma Aulacogen is primarily composed of basaltic dikes, gabbros, and units of granitic rock.〔 ==Description== The Southern Oklahoma Aulacogen extends roughly 500 miles long (805 km) by ~80–90 miles wide (129–145 km). The two remaining continental plate boundary arms of the triple junction from which the Southern Oklahoma aulacogen formed became spreading zones for the spreading of the Iapetus Ocean during the breakup of the supercontinent, Rodinia, estimated to have occurred in the Cryogenian Period, approximately 750 million years ago.〔 These arms closed in the Pennsylvanian Period (~323.2–298.9 Ma) and formed part of the Ouachita orogenic belt. The Southern Oklahoma Aulacogen is estimated to contain over 250,000 km3 of igneous rock. The aulacogen is inverted: rather than extending across the surface it penetrates into the North American craton, and is aligned with the northern edge of a deeply buried Proterozoic basin of uncertain origin which may have formed through igneous layering or deposition.〔 The aulacogen terminates on contact with the Ouachita orogenic belt. The Southern Oklahoma Aulacogen is associated with a widespread anomalous area in which seismic waves travel more slowly. A common comparison is drawn from this aulacogen to the Dniepr-Donets Aulacogen in Baltica because both are significant intracratonic rifts. The Southern Oklahoma Aulacogen contains numerous igneous rocks. Among these rocks are a multitude of gabbros, including anorthosite, titanium-rich, iron-rich, phosphorus-rich, and biotite gabbros.〔 Also included are rhyolites and granites. This assemblage is very similar to the mid-Proterozoic age anorthosite-mangerite-charnockite-granite (AMCG) complexes of North America, but for the lack of coarse massif anorthosites. This is significant in that AMCG complexes tend to form at huge depths in the Earth's crust and thus cool more slowly, allowing the massif anorthosites to form coarse-grained. The similar igneous assemblage suggests that the magmas that formed the igneous rocks of the Southern Oklahoma Aulacogen quickly cooled to at or near their crystallization point, much more quickly than the magmas of AMCG complexes, thus resulting in finer-grained anorthosites. More recently, different interpretations of seismic and outcrop data, as well as stratigraphy in the area have led some studies to postulate that this formation may not be an aulacogen after all, but a system of transform faults. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Southern Oklahoma Aulacogen」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.