Using vertical dikes as a new approach to constraining the size of buried craters: An example from Lake Wanapitei, Canada

Abstract

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 fi eld 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 fi eld, up to a maximum diameter of 3 km. Dikes L'Heureux, E., Ugalde, H., Milkereit, B., Boyce, J., Morris, W., Eyles, N., and Artemieva, N., 2005, Using vertical dikes as a new approach to constraining the size of buried craters: An example

3D gravimetric investigation of the Cerro do Jarau structure, Rio Grande do Sul, Brazil

“…This kind of target lithology makes its identification more difficult, because stratified targets provide better evidence of impact. This 7-km structure, however, is also the host of a dike swarm of 1200 Ma, a feature that helps the comprehension of the rocks below the surface based on magnetic studies (L'Heureux et al 2005). Ugalde et al (2006) suggest that the N-S trend observed in the gravity anomaly map is related to a regional fault zone of 2200-1900 Ma that has gone through reactivation over time.…”

“…This 7‐km structure, however, is also the host of a dike swarm of 1200 Ma, a feature that helps the comprehension of the rocks below the surface based on magnetic studies (L'Heureux et al. ). Ugalde et al.…”

Regularized 2D Savitzky–Golay derivative filter in estimating the second vertical derivative of potential field data

“…Careful observation suggests the presence of a characteristic pattern of dyke swarms, that is, those dykes remain parallel to subparallel to each other. The dyke swarm at Lake Wanapitei is assumed to be associated with Precambrian Matachewan and Sudbury dyke swarms (L'Heureux et al ., 2005), and such a swarm is interpreted to be due to the mantle plume effect (Ernst et al ., 1995).…”