La tectonique du front appalachien dans la région de St-Dominique, Québec

Abstract

The 'St-Dominique crest' (Quebec) represents one of the best exposed thrust slices in the external domain of the Appalachians (Ordovician). The observation and analysis of the main deformations show in particular that the apparent discontinuity of the stratigraphic units cannot be explained by transversely faulted blocks, and indicate that the 'crest' is not part of a collapsed structure, as suggested by previous authors. On the contrary, the apparently discontinuous formations can be explained by a succession of 'en échelon' folding. The fracturing, which allows small internal imbricated structures, is in harmony with this moderately folded framework and is also compatible with the relative displacements of imbricated compartments on the front and on the monoclinal side of the slice. Succeeding the compression phase, a tension phase induced an additional downward movement along some fault planes.On a small scale, an interesting model of folding and imbricated structures, useful to under-stand the larger imbricated slices of the regional Appalachian frontal domain, is offered by this structure.The lack of transverse faulting along the slice and the fact that the slice is plunging at both extremities suggests that the inference of transverse faulting along the outer Appalachian front in the Quebec area needs reexamination.