Abstract

The Charlevoix semi-circular structure, located 100 km northeast of Quebec City, possesses a rim 54 km in diameter, a ring-shaped graben with outcrops of Ordovician limestone, and an inner part flat or slightly undulating with a diameter of 32 km, in the middle of which rises Mont des Eboulements.This inner part is very fractured, and contains shatter cones and red and green breccias with aphanitic components. In the central part of the structure the rocks contain small veinlets and irregular masses of pseudotachylite, and the minerals display deformation features typical of rocks subjected to a violent shock. Quartz and feldspar alteration have produced an amorphous white substance. Heterogeneous breccias and fused rocks are visible in one outcrop and in blocks left by glacial erosion.This structure resembles other circular structures in Quebec, particularly those of West Clearwater Lake and Lakes Manicouagan and Mouchalagan. A volcanic origin is suggested by its location on the margin of the St. Lawrence Valley tectonic system, but the rapidity of the event and the violence of the shock reminds one rather of a meteorite origin.

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