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

Abstract

True three‐dimensional reflector orientations can be derived from prestack seismic reflection data where a seismic profile is particularly crooked. This is accomplished by estimating a measure of coherency along travel time trajectories defined by the azimuth, dip, and depth of a reflector and the medium velocity. Results from Lithoprobe line 48, located in the Opatica belt of the Archean Superior Province, differentiate reflectors with two distinct orientations, which coincide with the attitudes of two deformational fabrics mapped at surface. Assuming a connection between reflectivity and strain induced by tectonic processes, 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 shallowly to the north and to the south, indicate that most of the reflectors in the southern Opatica and beneath the Abitibi greenstone belt at middle and lower crustal levels formed during a later, approximately N‐S shortening event. Mantle reflections previously interpreted as a relict suture of an Archean subduction zone dip to the north at around 30°–45° and are also associated with this N‐S event. The distribution of reflector orientations estimated at the crooked parts 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 lower crust, characterized by the earlier D1 reflectors, is preserved in the central part of the belt.