Sudbury Basin instance of impact crater
The Sudbury Basin (), also known as Sudbury Structure or the Sudbury Nickel Irruptive, is a major geological structure in Ontario, Canada. It is the third-largest known impact crater or astrobleme on Earth, as well as one of the oldest. The crater was formed 1.849 billion years ago in the Paleoproterozoic era.The basin is located on the Canadian Shield in the city of Greater Sudbury, Ontario. The former municipalities of Rayside-Balfour, Valley East and Capreol 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.
An Ontario Historical Plaque was erected by the province to commemorate the discovery of the Sudbury Basin.Formation
The Sudbury basin formed as a result of an impact into the Nuna supercontinent from a meteor approximately 10–15 km (6.2–9.3 mi) in diameter that occurred 1.849 billion years ago in the Paleoproterozoic era.
Debris from the impact was scattered over an area of 1,600,000 km2 (620,000 sq mi) thrown more than 800 km (500 mi); and ejecta — rock fragments ejected by the impact — have been found as far away as Minnesota.Models suggest that for such a large impact, debris was most likely scattered globally, but has since been eroded. Its present size is believed to be a smaller portion of a 130 km (81 mi) round crater that the meteor originally created. Subsequent geological processes have deformed the crater into the current smaller oval shape. Sudbury Basin is the third-largest crater on Earth, after the 300 km (190 mi) Vredefort impact structure in South Africa, and  the 180 km (110 mi) Chicxulub crater under Yucatán, Mexico.
Geochemical evidence suggests that the impactor was likely a chondrite asteroid or a comet with a chondritic component.Structure
The full extent of the Sudbury Basin is 62 km (39 mi) long, 30 km (19 mi) wide and 15 km (9.3 mi) deep, although the modern ground surface is much shallower.The main units characterizing the Sudbury Structure can be subdivided into three groups: the Sudbury Igneous Complex (SIC), the Whitewater Group, and footwall brecciated country rocks that include offset dikes and the Sub layer. The SIC is believed to be a stratified impact melt sheet composed from the base up of sub layer norite, mafic norite, felsic norite, quartz gabbro, and granophyre.The Whitewater Group consists of a suevite and sedimentary package composed of the Onaping (fallback breccias), Onwatin, and Chelmsford Formations in stratigraphic succession. 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 sub layer.Because considerable erosion has occurred since the Sudbury event, an estimated 6 km (3.7 mi) in the North Range, it is difficult to directly constrain the actual size of the diameter of the original transient cavity, or the final rim diameter.The deformation of the Sudbury structure occurred in five main deformation events (by age in Mega years):
type of example of manifestation of representation of