Sudbury Basin

The Sudbury Basin, also known as Sudbury Structure or the Sudbury Nickel Irruptive, is the second largest known impact crater or astrobleme on Earth, and a major geologic structure in Ontario, Canada.

The basin is located on the Canadian Shield in the city of Greater Sudbury, Ontario. The former municipalities of Rayside-Balfour and Valley East lie within the Sudbury Basin, which is referred to locally as "The Valley". The urban core of the former city of Sudbury lies on the southern outskirts of the Basin.

The Sudbury Basin is located near a number of other geological structures, including the Temagami Magnetic Anomaly, the Lake Wanapitei impact crater and the western end of the Ottawa-Bonnechere Graben, although none of the structures are directly related to each other in the sense of resulting from the same geophysical processes.

Formation and structure

The Sudbury Basin is 62 km long, 30 km wide and 15 km deep. It was created as the result of a 10 km meteorite impact that occurred 1.85 billion years ago in the Paleoproterozoic era. Debris was scattered over an area of 1.6 million square kilometers and travelled over 800 kilometers away. [Associated Press: " [http://www.startribune.com/462/story/1304335.html Ontario crater debris found in Minn.] ", "Star Tribune", July 15, 2007] Its present size is believed to be a smaller portion of a 250 km round crater that the bolide originally created. Subsequent geological processes have deformed the crater into the current smaller oval shape. Sudbury Basin would then be the second largest crater on Earth, after the 300 km Vredefort crater in South Africa, and larger than the 170 km Chicxulub crater in Yucatán, Mexico.

The main units characterizing the Sudbury Structure can be subdivided into threegroups: the Sudbury Igneous Complex (SIC), the Whitewater Group, and footwallbrecciated country rocks that include offset dikes and the Sublayer. TheSIC is believed to be a stratified impact melt sheet composed from the base up of Sublayernorite, mafic norite, felsic norite, quartz gabbro, and granophyre. The Whitewater Group consists of a suevite and sedimentary package composed ofthe Onaping (fallback breccias), Onwatin, and Chelmsford Formations in stratigraphicsuccession. Footwall rocks, associated with the impact event, consist of Sudbury Breccia(pseudotachylite), footwall breccia, radial and concentric quartz dioritic breccia dikes(polymict impact melt breccias), and the discontinuous Sublayer. Because considerable erosion has occurred since the Sudburyevent, an estimated 6 km in the North Range, it is difficult todirectly constrain the actual size of the Sudbury crater, whether it being the diameter of theoriginal transient cavity, or the final rim diameter.

The deformation of the Sudbury structure occurred in four main deformation events (by age):

# the Penokean orogeny (1900 Ma)
# intrusion of the Sudbury Igneous Complex (1844 Ma)
# the Grenville orogeny (1400 - 1000 Ma)
# the Lake Wanapitei impact (37 Ma)

Modern uses

The large impact crater filled with magma containing nickel, copper, platinum, palladium, gold, and other metals. As a result of these metal deposits, the Greater Sudbury area is one of the world's major mining communities. The region is one of the world's largest suppliers of nickel and copper ores. Most of these mineral deposits are found on the outer rim of the Basin.

Due to the high mineral content of its soil, the floor of the Basin is among the best agricultural land in Northern Ontario, with numerous vegetable, berry, and dairy farms located in the Valley. However, due to its northern latitude, it is not as fertile as agricultural lands in the southern portion of the province. Accordingly, the region primarily supplies products for consumption within Northern Ontario, and is not a major food exporter.

References

Pye, E.G., Naldrett, A.J. & Giblin, P.E. (1984) The Geology and Ore Deposits of the Sudbury Structure, Ontario Geological Survey, Special Volume 1, Ontario Ministry of Resources

External links

* [http://www.unb.ca/passc/ImpactDatabase/ Earth Impact Database]
* [http://www.ottawa.rasc.ca/articles/odale_chuck/earth_craters/sudbury/index.html Aerial Exploration of the Sudbury Crater]
* [http://fgms.home.att.net/sudbury.htm Fallbrook Gem and Mineral Society - Sudbury Structure page]