Impact modeling and post-impact cooling studies predict a unique fracture and post-impact temperature distribution within the crater floor of large meteorite impact structures. The integration of numerical modeling results and their application to the observed geophysical and current topographic data provides new insights into the early evolution of the deeply eroded Sudbury Structure. The modeling shows a maximum depth of melting of 30–40 km (depending on impact angle and impact velocity). However, melt from upper target layers (< 10 km) is mainly ejected during the excavation stage of crater formation, and the remaining melt is strongly biased to melt derived from lower crustal material. Two-dimensional thermal evolution modeling with various granophyre/norite thickness ratios shows that irrespective of the granophyre/norite thickness ratio, the hottest part of the Sudbury Igneous Complex (SIC) was near the crater center at the melt-pool bottom and within the crater floor, which supports precipitation of sulfides toward the crater floor. The 2D cooling models give compelling evidence for longevity of melt at the bottom of the SIC and partial remelting of the crater floor. The numerical model results are compared with observed topographic, seismic and magnetic data and provide important constraints on their interpretation. A unique slow cooling history is manifested in the broad magnetic signature of the SIC and the adjacent crater floor, and its pronounced remanent magnetization. The vast damage zone and the complex fracture pattern predicted for the crater floor is well preserved in the new high-resolution topographic data for the Sudbury Structure. These regional topographic data allow the distinction between inside-basin fabric (radial topographic lineaments) and crater-floor topographic fabric (radial and contact parallel lineaments), which corroborates the numerical modeling results of radial and concentric faults propagating up to tens of kilometers from the crater center.

Lake Wanapitei, located within the Southern Province of Ontario, Canada, provides the setting for a unique study of an impact crater situated within a shield environment. Evidence for the 7.5-km-diameter Wanapitei impact includes a circular Bouguer gravity low centered over the central area of the lake and features of shock metamorphism in samples of glacial drift found on the southern shores. Geophysical studies of craters in hard-rock environments are often limited by the lack of markers used for exploration; this may be overcome with the use of the large igneous dike swarms that characterize Archean terrains. The 1.2 Ga Sudbury dike swarm predates the impact that is suggested to have generated Lake Wanapitei and provides the setting for a study to constrain the size and location of the impact crater. The swarm is clearly visible on aeromagnetic maps as high amplitude, linear features, suggesting they could be used as vertical markers indicative of structural changes having an effect on target rock susceptibilities. To fully establish the size of the crater, a total field magnetic map was produced to trace the Sudbury dikes through the proposed crater center. A gap in their signature, expressed as a 100 nT low, 2–3 km in width, constrains the size of the crater to <5 km. Numerical modeling suggests that a crater of this size will demagnetize target rocks, producing a low in the total magnetic field, up to a maximum diameter of 3 km. Dikes