Sudbury
A giant impact that left one of the world's richest metal deposits.
Key facts
- When
- about 1.85 billion years ago
- Where
- Ontario, Canada
- What hit
- an asteroid or comet perhaps 10 to 15 km across
- Era
- Deep time
- Location
- 46.60° N, 81.20° W
Of the order of a hundred million megatons of TNT, comparable to Chicxulub.
Similar to the impact that ended the age of the dinosaurs.
What happened
The Sudbury Basin in Ontario is the deformed remains of an impact crater that may originally have been about 200 km across. Folding of the crust since then has squeezed it into an oval about 60 km long.
The impact melted a huge volume of crust. As that sheet of melt, more than 2 km thick, cooled and separated, heavy metal-rich liquid sank to its base and formed rich deposits of nickel, copper and platinum-group metals. The mines of Sudbury have produced metal for more than a century.
Whether the impactor was an asteroid or a comet is still discussed; some chemical traces have been read as pointing to a comet.
Effects
Ejecta from Sudbury has been found in layers in Minnesota and around Lake Superior, as far as about 800 km from the crater, showing how far the blast threw debris.
The evidence
Shatter cones in the surrounding rocks, shocked quartz, breccias and the vast impact melt sheet itself, known as the Sudbury Igneous Complex.
Did you know?
Apollo astronauts visited Sudbury in 1971 to learn to recognise impact rocks before going to the Moon.
For a long time geologists thought Sudbury was a volcanic structure; the discovery of shatter cones in the 1960s showed it was an impact.
Related pages
How is impact energy measured? See energy explained, or try the impact calculator.