SALVAGE GEOLOGY: AN EXAMPLE FROM SUDBURY, ONTARIO

This paper presents an example of salvage geology, in which critical field evidence from a recently-formed exposure bearing on a major geologic problem has been found. The problem is the size and shape of the Sudbury Structure of northern Ontario, a 60 b y 30 km feature generally accepted as a Proterozoic impact basin formed 1845 m.y. ago. The original diameter of the Structure is widely believed to have been over 200 km. One line of evidence is the distribution of "Sudbury Breccia," proposed as having been formed directly or indirectly, as pseudotachylite, by the impact that produced the Structure. A new exposure of Sudbury Breccia on the South Range was created when Highway 144 was widened in the late 1990s. The breccia here is part of a Sudbury Swarm diabase dike, cross-cutting the Sudbury Igneous Complex and well-dated at 1238 m.y.. It cannot possibly be related to the impact that formed the Structure. It resembles many other dike-related "Sudbury Breccia" occurrences north of the Structure. This exposure should be given intensive study, since further road widening may destroy it.