Breccia Outcrop in Manicouagan Impact Structure

January 12, 2007


Provided by: Charles O'Dale
Summary authors & editors: Charles O'Dale

This photo illustrates a typical breccia outcrop found within the central peak area of the Manicouagan Impact Structure located in Quebec, Canada. Approximately 214 million years ago, an estimated 10 kilometre (6.2 mile) wide bolide impacted here at a velocity of between 12 and 30 kilometres (7.4 and 18.6 miles) per second. The resultant 100 kilometre (62 mile) diameter crater is one of the largest impact craters still preserved on the surface of the Earth. The water filled circular annular moat that is prominent in space images is only one third of the size of the original crater. This moat fills a ring where impact-brecciated rock was eroded away by glaciation.

At the point of impact, the rocks were instantaneously evaporated/melted/shattered by the energy released. The shattered white "country" rocks shown on the image were imbedded in what is interpreted to be a fine grained matrix impact melt. It's possible that the extremely small size of the grains within the matrix were formed by the very high pressure of the gas generated when the bolide impacted. The heat released was so intense that it's believed it took 1,600 to 5,000 years before the melted rocks cooled. This breccia outcrop is found in an inlet, cut into the central peak of the impact structure, known as Memory Bay.

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