Abstract

Gravity traverses were made along the Rivière aux Pékans and along the Mushalagan River in west-central Québec in 1964 and 1966 in order to make a closer investigation of the large, negative Bouguer anomaly discovered near the Grenville Front in west-central Québec by field parties of the Dominion Observatory in 1956. Detailed elevations were available on both of these traverses from hydrological studies carried out earlier by the Department of Natural Resources of the Province of Québec and by Hydro-Québec.Both gravity profiles traversed the main negative feature plus a large positive rise in the Bouguer anomaly immediately south of the Grenville Front. There are very few clues from the surface geology as to what might be the causes of these effects. The combined analysis of gravitational and aeromagnetic data suggests that one possible interpretation is that the negative anomaly is caused by a deep infold of lighter, non-magnetic (possibly metasedimentary) material quite near the surface, and that the positive rise is due to a slight increase in the average density within the intermediate zone of the Grenville crust.

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