ARE OUTLIERS OF THE HURONIAN SUPERGROUP PRESERVED IN STRUCTURES ASSOCIATED WITH THE COLLAPSE OF THE SUDBURY IMPACT CRATER

Several outliers of the Paleoproterozoic Huronian Supergroup are prese rved in a 20 km wide arcuate belt northwest of the Sudbury Igneous Com plex. Forty years ago it was suggested that these outliers represented the remnants of a discontinuous rim syncline developed around a domal structure. Thirteen years later it was proposed that they were preser ved in grabens formed as a result of collapse of the central uplift of a multi-ring impact crater and the simultaneous emplacement of the Su dbury Igneous Complex. This interpretation has been accepted by most i nvestigators without question, to the extent that the position of the outliers has been used to estimate the size of the supposed crater. Ou r observations indicate that Huronian strata in the outliers were depo sited in a series of paleo-valleys on a terrane with considerable topo graphic relief. The asymmetric nature of the fill in some of the outli ers suggests deposition may have taken place in half-grabens. The outl iers are preserved in synclines developed by orogenic activity prior t o the 1850 Ma impact event. They are cut by later transverse and longi tudinal faults. The geometry of the outliers, combined with the charac ter and directional attributes of the sedimentary fill, indicates that the outliers are not related to the Sudbury Event.