Detailed study of the Moho boundary in the Superior province of Quebec.

English Abstract:

Our project focuses on the description of the Moho discontinuity beneath the Superior Province in Quebec. We determine the depth to the Moho, its sharpness, and investigate such attributes as inclination, and relationships with the other discontinuities within the crust.

Our highly descriptive observations are facilitated by a large amount of clear data collected over a decade from long-operating seismic stations in Quebec. Also, we include data gathered by a temporary seismic array placed between Charlevoix and James Bay. We use teleseismic P wave data and carry out receiver function analysis to identify P to S converted waves.

To investigate the sharpness of the Moho we examine the shape of the P-to-S converted phase associated with it at different frequencies, from 0.25Hz to 2-3 Hz. To determine whether there is a systematic dip in the Moho we use directional changes in the timing of this pulse.

In the northern part of the Superior Province the Moho is very sharp. Converted waves with frequencies up to 2Hz are observed, suggesting a vertical change in seismic properties over a few hundred meters. This is not the case close to the Grenville Front, where a complex signature at high frequencies suggests a more diffuse crust-mantle boundary.

A very clear signature of the regional dip in the Moho is found at a site close to James Bay, while sites further south show a relatively flat Moho boundary. The finding of a dipping Moho in the oldest part of the Canadian Shield is surprising, and documents long preservation of the signature of past tectonic events.

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