Under the auspices of the Great Lakes International Multidisciplinary Program on Crustal Evolution (GLIMPCE), coincident steep-and wide-angle seismic reflection data sets were acquired in Lake Huron. The wide-angle data were recorded at stationary onshore receivers during the shooting and recording of the conventional marine steep-angle survey. To extract information from the wide-angle data, a variety of processing techniques including automatic trace editing, amplitude balancing, F-K filtering, static corrections, and predictive deconvolution were applied to the wide-aperture commonreceiver gather before migration. The application of a slowness-weighted depth migration algorithm, which was first tested on synthetic data and which included a slowness filter, resulted in an image of the Grenville Front tectonic zone (GFTZ) remarkably similar to that observed in the multichannel steep-angle section. The migrated wide-angle data suggest that prominent bands of east dipping seismic reflections observed across the GFTZ extend unattenuated to depths of at least 45 km.
An expanding spread seismic reflection survey has been conducted across the Snake Bay–Kakagi Lake greenstone belt in northwestern Ontario. Receiver and shot arrays with multiple shots per location helped to maintain a high signal to noise ratio in most of the data. Distances between the shots and receivers ranged from 1.04–8.48 km and the total charge per shot location varied from 26–86 kg. After computer processing the data, numerous coherent reflections were observed from near vertical and near horizontal discontinuities.Prominent early reflections were used to map a granite–greenstone contact to the south of the profile and a section of the Long Bay fault zone to the northeast of the profile. A noticeable absence of reflections from the Aulneau granite batholith–greenstone contact suggests that this contact dips westwards, towards the centre of the batholith.From the later reflections a model of the deep crust beneath the Snake Bay–Kakagi Lake greenstone belt was derived. This model, which represents a lateral extension of the Aulneau crustal model, consists of a three-layered crust. The top crustal layer is 19 km thick with Pg and Sg velocities of 6.2 and 3.5 km/s respectively, the middle layer is 3 km thick, and the lower layer extends to the Mohorovicic discontinuity at 38 km depth.
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