The Grenville Front Tectonic Zone: Results from the 1986 Great Lakes Onshore Seismic Wide‐Angle Reflection and Refraction Experiment

Abstract

The Grenville Front, which marks the orogenic boundary between the Archean Superior Structural Province and the much younger Grenville Province to the southeast, is one of the major tectonic features of the Canadian Shield. Within Canada, it is approximately 1900 km in length extending from the north shore of Lake Huron across Ontario and Quebec to Labrador. In 1986, a major coincident onship near‐vertical reflection and onshore wide‐angle reflection/refraction experiment (GLIMPCE–Great Lakes International Multidisciplinary Program on Crustal Evolution) was conducted along a series of lines across the Great lakes. One of the lines, line J, ran across Georgian Bay and Lake Huron for a distance of 350 km and crossed the Grenville Front Tectonic Zone (GFTZ). The seismic signals from the air gun array source were well recorded by the onshore stations up to distances of 250 km with a seismic trace spacing of 50–62.5 m. The GFTZ had a profound effect on the nature of the reflector patterns observed on the onshore seismic sections. Data recorded by the stations on the east end of the line indicate that the crustal P phases are very complex and form a “shinglelike” pattern of reflected waves. Data recorded by stations at the center and at the western end of the line show that the Pg phases are normal and lack the shinglelike appearance. This character of arrivals was also observed on the corresponding S wave sections. A combined P and S wave forward modeling analysis shows that the GFTZ is composed of bands of reflectors dipping at angles of 20°–35° extending to the lower crust. These reflectors were also well imaged on the coincident near‐vertical reflection data. Reflectors under the Britt domain to the east of the GFTZ have a shallower dip than those along the zone. The structure of the crust under the Manitoulin terrane to the west of the GFTZ is laterally homogeneous with a major intracrustal reflector at a depth of 17–20 km below the surface. Poisson's ratio is slightly higher to the east of the Grenville Front compared to the region to the west. The travel times of the PmP signals indicate that the Moho may be deeper under the GFTZ than under the surrounding regions. Our results give added support to tectonic theories that the Grenville Front owes its origin to a continental collision process.

Crustal velocity structure associated with the eastern Tennessee seismic zone: Vp and Vs images based upon local earthquake tomography

“…A pre‐Grenville age is usually associated with this intrusion and other intrusions forming the ECGH based upon geophysical and geological similarities with the 1.1 Ga U‐Pb age‐dated MCR [ Van Schmus and Hinze , ]. The location of the Front, the westernmost location of deformation and high‐grade metamorphism associated with the Grenville orogeny, is enigmatic south of exposures in Canada and below Lake Huron [ Epill and Mereu , ]. What is probably the Grenville Front is imaged in COCORP line OH‐1 located in west central Ohio [ Pratt et al ., ; Culotta et al ., ].…”

Modeling wide‐angle seismic data for crustal structure: Southeastern Grenville Province

“…Epili and Mereu [1991] imaged steeply dipping reflectors with wide-angle data and associated positive velocity discontinues with each. A single linear reflecting horizon was assigned to each Pr branch and its spatial orientation determined through travel time inversion after the velocity structure had been obtained by modeling the primary refracted and reflected phases.…”

Regional study of the Archean to Proterozoic crust at the Sudbury Neutrino Observatory (SNO+), Ontario: Predicting the geoneutrino flux

“…We use the published 1:5,000,000 scale Geological Map of North America [ Reed et al ., ] to describe the surface geological characteristics in the six 2°× 2° crustal tiles centered at SNO+ (outlined in Figure ), including lithologies, boundaries between different geological terranes/provinces, and their relative proportions. Refraction seismic surveys carried out in this region provide information on the crustal velocity structure and thickness [ Mereu et al ., ; Epili and Mereu , ; Percival and West , ; Musacchio et al ., ; Winardhi and Mereu , ], whereas reflection seismic surveys and receiver function analysis provide additional constraints on the Moho depth (Figure b) [ Brown et al ., ; Eaton et al ., ; Spence et al ., ]. All of the above information is integrated into a 3‐D regional crust model.…”