| 翻訳と辞書 |
| Manicouagan crater ： ウィキペディア英語版 |
Manicouagan crater
The Manicouagan Crater is one of the oldest known impact craters and is the largest 'visible' impact crater on Earth, located primarily in Manicouagan Regional County Municipality in the Côte-Nord region of Québec, Canada,〔 about north of the city of Baie-Comeau. At roughly 213-215 million years old, Manicouagan is one of the oldest large astroblemes still visible on the surface. Its northernmost part is located in Caniapiscau Regional County Municipality. It is thought to have been caused by the impact of a diameter asteroid about 215.5 million years ago (Triassic Period).〔Ramezani, J., S. A. Bowring, M. S. Pringle, F. D. Winslow, III, and E. T. Rasbury (2005). "The Manicouagan impact melt rock: a proposed standard for intercalibration of U-Pb and 40Ar/39Ar isotopic systems". 15th V.M. Goldsmidt Conference Abstract Volume, p. A321.〕 It was once thought to be associated with the end-Carnian extinction event.
The crater is a multiple-ring structure about across, with its diameter inner ring its most prominent feature; it contains a diameter annular lake, the Manicouagan Reservoir, surrounding an inner island plateau, René-Levasseur Island. It is the earth's sixth-largest confirmed impact crater according to rim-to-rim diameter.〔(【引用サイトリンク】url=http://www.passc.net/EarthImpactDatabase/Diametersort.html )〕
==Hypothetical multiple impact event==
It has been suggested that the Manicouagan crater may have been part of a multiple impact event which also formed the Rochechouart crater in France, Saint Martin crater in Manitoba, Obolon' crater in Ukraine, and Red Wing crater in North Dakota. Geophysicist David Rowley of the University of Chicago, working with John Spray of the University of New Brunswick and Simon Kelley of the Open University, discovered that the five craters formed a chain, indicating the breakup and subsequent impact of an asteroid or comet,〔Spray, J.G., Kelley, S.P. and Rowley, D.B. (1998). "Evidence for a late Triassic multiple impact event on Earth". ''Nature'', v. 392, pp. 171-173. (Abstract )〕 similar to the well observed string of impacts of Comet Shoemaker-Levy 9 on Jupiter in 1994.
Kelley had developed a technique to precisely date impact craters, using laser argon-argon dating of the glass formed by the impacts, and cited stratigraphic evidence to support an older age of 215 million years (Late Triassic). He and Kelley sought Rowley's help to determine how the craters were aligned when the impacts occurred, since—due to plate tectonics—the locations have moved large distances in the intervening 214 million years. Three of the craters—Rochechouart, Manicouagan and Saint Martin—formed a chain at latitude 22.8° N, while Obolon' and Red Wing lay on identical declination paths with Rochechouart and Saint Martin respectively. All of the craters had previously been known and studied, but their paleoalignment had never before been demonstrated. Rowley has said that the probability that these craters could be aligned like this due to chance is nearly zero.
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「Manicouagan crater」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.
|
|