Structural fabric of the Central Metasedimentary Belt of southern Ontario, Canada, from deep seismic profiling |
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| Authors: | CR O'Dowd D Eaton D Forsyth HW Asmis |
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| Institution: | aDepartment of Earth Sciences, University of Western Ontario, London, Ontario, Canada N6A 5B7;bContinental Geoscience Division, Geological Survey of Canada, 615 Booth St., Ottawa, Ontario, Canada K1A 0E9;cOntario Power Generation, 700 University Ave., Toronto, Ontario, Canada M5G 1X6 |
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| Abstract: | The Central Metasedimentary Belt boundary tectonic zone (CMBbtz) is a 10–20-km-wide zone of intense structural deformation within the 1.3–1.0 Ga Grenville orogen of southeastern Canada. The crustal structure of the exposed CMBbtz has been well studied, but its sub-Phanerozoic location and geometry beneath the urban development and nuclear stations of the Toronto region are not well known. A new 75-km Lithoprobe reflection profile acquired close to Toronto provides a clear image of the CMBbtz as a panel of southeast-dipping reflections that extends with moderate dip (<25°) to mid-crustal depth (25 km). These dipping reflections truncate and (or) overprint a subhorizontal band of reflectivity at 21 km depth. The seismic line is oblique to the major structural trends; cross-dip analysis shows that the southeast-dipping reflections have a strike and dip of N13°E and 25°, whereas the “subhorizontal” reflections strike and dip at N65°E and 20°, respectively. Both of these bands of reflectivity can be correlated to magnetic anomalies in the CMBbtz or its immediate footwall. Magnetic anomalies with similar strike directions are well expressed within a distinct rhomboid-shaped region (106×109 km) in the subsurface of western Lake Ontario, herein named Mississauga domain. Taken together, the seismic and magnetic data are inconsistent with existing models, in which the CMBbtz is extrapolated beneath Lake Ontario along a linear magnetic anomaly. We propose a revised subsurface trace of the CMBbtz along the western edge of the Mississauga domain. Small earthquakes in western Lake Ontario appear to cluster along trends co-linear with ENE magnetic anomalies, suggesting a possible degree of basement tectonic control on local intraplate seismicity. |
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| Keywords: | Grenville orogen Crustal structure Seismic-reflection profile Seismic processing Central Metasedimentary Belt |
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