A LINK BETWEEN DEFORMATION HISTORY AND THE ORIENTATION OF REFLECTIVE STRUCTURES IN THE 2.68-2.83-GA OPATICA BELT OF THE CANADIAN SUPERIOR PROVINCE

True three-dimensional reflector orientations can be derived from pres tack seismic reflection data where a seismic profile is particularly c rooked. This is accomplished by estimating a measure of coherency alon g travel time trajectories defined by the azimuth, dip, and depth of a reflector and the medium velocity. Results from Lithoprobe line 48, l ocated in the Opatica belt of the Archean Superior Province, different iate reflectors with two distinct orientations, which coincide with th e attitudes of two deformational fabrics mapped at surface. Assuming a connection between reflectivity and strain induced by tectonic proces ses, the reflectors with NNE strikes and shallow dips toward the east are correlated with surface evidence for early west vergent thrusting in the Opatica belt. Other reflectors, which strike ENE-WSW and dip sh allowly to the north and to the south, indicate that most of the refle ctors in the southern Opatica and beneath the Abitibi greenstone belt at middle and lower crustal levels formed during a later, approximatel y N-S shortening event. Mantle reflections previously interpreted as a relict suture of an Archean subduction zone dip to tl-le north at aro und 30 degrees-45 degrees and are also associated with this N-S event. The distribution of reflector orientations estimated at the crooked p arts of line 48 indicates that much of the Opatica crust was reworked during the N-S shortening event, although a region of the middle and l ower crust, characterized by the earlier D-1 reflectors, is preserved in the central part of the belt.