Structural analysis of the central and southwestern Sudbury Structure, Southern Province, Canadian Shield

Abstract

The Sudbury Structure (SS) is an unusual crater structure which acquired its present oval surface shape during northwest-directed ductile thrusting. Lower amphibolite-facies metamorphism accompanied the thrusting which generated a major reverse shear zone. At least 50 km long, the South Range shear zone (SRSZ) transects the South Range of the Sudbury Structure and exhumes a low level of the Sudbury Igneous Complex (SIC). Assuming heterogeneous simple shear in the northwest–southeast vertical plane on northeasterly striking glide surfaces, minimal estimates of net displacement across the SRSZ exceed 8 km. This displacement magnitude and the map pattern of the SIC require the southwest closure of the SS to be steeply plunging, in accord with a hypothetical funnel shape of the SIC. The rocks of the metasedimentary core of the SS are deformed into a family of second-order buckle folds, the tangent surface of which forms an upright open flexure within the first-order structure of the Sudbury synclinorium. The original orientation and bulk rotation of contacts in the SIC are unknown, so its participation in large-scale folding remains uncertain.