A paleomagnetic investigation of the sudbury basin offsets, Ontario, Canada

The Sudbury offsets are a series of dike-like structures that appear either to radiate out from, or parallel the main Sudbury irruptive. In an attempt to establish the tectonic and magmatic relationship of these offsets to the main irruptive over 50 sites from 8 offsets were sampled for a paleomagnetic survey. From the over 10,000 measurements it is possible to derive a number of conclusions. First, the offsets are the end product of at least four separate intrusive pulses exactly the same as the main irruptive. The initial formation of the offsets coincides with the intrusion of the norite in the main irruptive. Second, the oldest remanence direction from the offsets exhibits the same directional differences between the north and south ranges as is seen in the norite component of the main irruptive. The offsets must therefore have suffered the same magnitude and sense of tectonic rotations as the immediately adjacent sector of the main irruptive. Three remanence components appear to be intimately associated with the distribution of sulfide rich zones. Of these three, one undoubtedly records a period of magmatic sulphide deposition. The other two appear to be recording mineralization events which require longer periods of remanence blocking and possible models include remobilization and redeposition of pre-existing deposits, and secondary hydrothermal introduction of a new generation of sulphides.