FURTHER DEBATE ON THE ORIGIN OF THE SUDBURY STRUCTURE - IS IT RELEVANT TO THE VREDEFORT DOME AND THE BUSHVELD COMPLEX

The Sudbury Structure in Ontario is well-known for its unique nickel-c opper sulphide deposits. This formation - like the Vredefort Dome and, to a lesser extent, the Bushveld Complex in South Africa - has been t he subject of vigorous debate over its origin by either endogenous or exogenous (asteroid impact) processes. Extensive field and laboratory studies on the formation and evolution of the Sudbury Structure have r ecently been completed, and in 1992 an international conference was co nvened to review progress on the issue. This conference showed clearly that the majority of workers now believe that the new data support an impact origin. This article reviews the main arguments in the debate on the origin of the Sudbury Structure and summarizes remaining proble m areas. In addition, similarities and differences between the Sudbury Structure, on the one hand, and the Vredefort Dome and the Bushveld C omplex, on the other, are highlighted. It is the author's opinion that asteroid impact is the most likely cause of the Sudbury Structure. Fu rthermore, the possibility of an impact origin of the Vredefort Dome c annot be excluded, but more information is needed for confirmation. Ev idence for an impact origin of the Bushveld Complex is very limited, a nd further geological study of the margins around the Complex is neede d to provide support for or against this provocative hypothesis.