Abstract

Cambro-Ordovician greenschists and phyllites in the Shickshock Mountain area are characterized by a foliation S1 almost completely parallel to layering S0, and a mineral lineation apparently axial to obscure tight folds F1. Absence of these structures from Lower to Middle Ordovician argillites immediately to the north of the Shickshocks suggests that F1 folding and metamorphism occurred earlier than at least part of the Early Ordovician Epoch.The dominant folds F2, which affect all Lower and Middle Paleozoic rocks, trend northeast and include the Gaspé synclinorium with a Siluro-Devonian axial zone. F2 are upright to inclined, and an axial-surface fracture cleavage S2 forms a major fan divergent upward across the synclinorium. F2 hinges are generally low plunging; but some are curved as much as 90°, perhaps because of variable dip-slip on S2.Discontinuous folds F3 exposed only in Ordovician rocks on the north coast, have steep axial surfaces striking eastward oblique to northeast-trending S2 cleavage. Small kinks, F4, virtually restricted to the Shickshock schists with S1, form conjugate sets with steep to vertical northwest-trending kink planes. Later (?) low-dipping kink bands in Devonian argillites displace steep S2 sub-horizontally.The strain during F1 folding is not clear. F2, F3, and F4 possibly formed while near horizontal compression across axial surfaces progressively changed azimuth clockwise. The low-dipping kink bands may reflect late lateral expansion associated with uplift.

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