Date of Award
Doctor of Philosophy
The 1986 GLIMPCE (Great Lakes International Multidisciplinary Program on Crustal Evolution) seismic experiment was conducted by a number of research groups both from the USA and Canada in order to determine the structure of the crust beneath the Great Lakes region. The main tectonic targets were the Midcontinent Rift System (MRS), the Grenville Front Tectonic Zone (GFTZ), the Michipicoten Greenstone Belt, and the Penokean and Huronian Fold Belts. The University of Western Ontario participated in this experiment and acquired approximately 25,000 records over a 200 hour continuous recording period by operating its portable vertical component refraction instruments at five separate land stations: one at Michipicoten Island, one at Bruce Peninsula, and three at Parry Sound. In this research, I present the data processing techniques and interpretation of the onshore wide-angle reflection/refraction data and compare the results with the images which had previously been obtained in the coincident near-vertical reflection experiment.;A combined P and S wave forward modeling analysis applying ray theory to laterally heterogeneous models as well as a wide-angle migration analysis show that the GFTZ is composed of bands of mylonitized reflectors dipping at angles of 20 to 30 degrees right down to the lower crust. The 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 front is laterally homogeneous with a major intra-crustal reflector at a depth of 17-20 km below the surface. This reflector was detected by stations on both sides of Lake Huron and was also well imaged on the near-vertical reflection sections. Evidence from the PmP signals shows that the Moho may be thicker 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 model.;The analysis of the data for the N-S fan line which crossed the axis of the Lake Superior synclinal basin indicates that the P* is not a simple arrival but forms a rather complex pattern of irregular multiple arrivals. The wide-angle PmP reflection signals from the Moho are strong and well observed only for the shots fired near the ends of the lines. These results indicate that the Moho in that area is probably greatly disrupted. The N-S inline profiles showed the presence of a set of reflectors which was also mapped in the near-vertical reflection data. The observations support the results of earlier crustal studies in Lake Superior which showed that the crust under the eastern part of the lake was exceedingly thick and gives added support to the rift theory for the structure under the lakes.
Epili, Duryodhan, "Crustal Structure Beneath The Great Lakes: Results From The Glimpce Onshore Seismic Data" (1991). Digitized Theses. 1949.