THE SUDBURY STRUCTURE - CONSTRAINTS ON ITS GENESIS FROM LITHOPROBE RESULTS

Results of the LITHOPROBE transect provide additional corroboration of the impact model for the origin of the Sudbury Structure. High resolu tion seismic reflection data indicate that the Sudbury Igneous Complex (SIC) is indeed continuous under the Sudbury Basin. There is no indic ation of a feeder dike system or a previously assumed ''hidden mafic m ass''. All these observations strongly support the interpretation of t he SIC as a coherent impact melt sheet. In addition, the seismic, and to a lesser extent magnetic and gravity, results point to a highly ass ymmetric structure to the SIC at depth, with significant tectonic disr uption in the South Range. The present non-circularity of the SIC is c aused by post-impact ductile deformation and thrusting due to northwes t directed compression. Decompressing this strain pattern leads to an original diameter of the SIC between 60 and 80 km, which, in consequen ce, would extend the original diameter of the final crater up to a max imum of 280 km.