Shatter cones at Sudbury, Ontario, Canada (46°36'N, 81°11'W)

The photograph illustrates a series of shatter cones exposed at Sudbury. The Sudbury area has the dubious record of being the target area of two major impacts. The first caused the ca. 200-km-wide Paleoproterozoic impact (ca. 1850 my ± 3 my) that created the Sudbury Irruptive, and the second formed the nearby Wanapitei impact structure just 37 million years ago.

Shatter cones are conical fractures present in rocks. The shatter cones at Sudbury are clearly seen in the Huronian quartzites. These were first correctly identified by an American geologist, Robert Dietz, in 1964. He pointed out that they likely originated by intense shocking of the rock from a meteorite or asteroid impact. The Sudbury features range in size from several metres to a few centimetres. The one in the centre of the picture is about 1m. The impact hypothesis for Sudbury is supported by melt breccias and shocked mineral grains.

Sudbury is not the only place in the world that you can see such features and we point you to several web sites that you can investigate to find out more about these enigmatic structures.

Vredefort Shatter Cones (Africa)

http://www.lpl.arizona.edu/~rlorenz/vredshat.html

Beaverhead structure, Montana

http://htmlscript.duc.auburn.edu/academic/science_math/geology/docs/wetumpka /shatter.htm

For a more technical definition look at:
 http://www.geology.iastate.edu/new_100/shatter.html                                     
http://www.lpi.usra.edu/ (the Lunar and Planetary Institute) 
http://miac.uqac.uquebec.ca (the Meteorites and Impacts Advisory Committee to the Canadian Space Agency, alias MIAC)