Velocity structure of the Kapuskasing Uplift, northern Ontario, from seismic refraction studies

Abstract

A crustal scale seismic refraction experiment was conducted over the Kapuskasing structural zone, northern Ontario, in 1984. The zone cuts obliquely across the east‐west structural grain of the Superior Province in the Canadian shield and has been proposed as a cross section of Archean crust exposed by thrust faulting along the Ivanhoe Lake cataclastic zone during early Proterozoic time. Five seismic refraction lines of 360–450 km were shot over the area. There were 18 profile shots and two fan shots with a recorder spacing of 2–5 km. We have modeled the travel times and amplitudes of the data from the profile lines and analyzed reflections from the crust‐mantle boundary on the fan shots. We have imaged a low‐velocity zone under the Abitibi greenstone belt ranging from 4–5 to 9–12 km depth that is underlain by a highly reflective zone. There is a considerable deepening of the Moho from 40–43 km to 50–53 km under and to the west of the southern end of the Kapuskasing structural zone. A high‐velocity anomaly of 6.6–6.7 km/s has been imaged in the upper crust down to 20 km depth beneath the Kapuskasing structure with a suggested dip of 15°±2° to the west. This corresponds well to the proposed location of a granulite zone thrust up from the middle or lower crust in the early Proterozoic.