Abstract

The Gaspé Belt is the largest middle Paleozoic belt in the Canadian Appalachians. The most complete stratigraphic record of Upper Ordovician to Middle Devonian rocks of this belt occurs in the Gaspé Peninsula, in the northeastern part of the Québec re-entrant. Rocks of the Gaspé Belt rest unconformably on Cambrian to Ordovician rocks of the Humber and Dunnage zones, and are unconformably overlain by Carboniferous rocks. The regional metamorphic grade of the Gaspé Belt rocks is very low, and some units are still in the oil window.

The deformation history of the Gaspé Belt rocks comprises multi-stage deformation events represented by two phases. A Late Silurian to Early Devonian phase, the Salinic disturbance, manifested by an unconformity, NW-trending folding, synsedimentary faulting, and intra-plate volcanism. The late Early to Middle Devonian Acadian phase is recorded by NE-trending folding, cleavage development and both reverse and strike-slip faulting within a transpressive setting during the oblique continental collision between Laurentia and Avalon (a peri-Gondwanan terrane), which took place farther southeast. The tectonic setting during the Salinic disturbance is consistent with continuous plate convergence (without subduction) after the Taconian Orogeny and before the Acadian continental collision.

The paleogeographic maps of the Gaspé Belt during Pridolian, Pragian and Emsian times reflect the tectonic activity south of the Gaspé Peninsula. The switch from sinistral to dextral relative motion between Laurentia and Avalon terranes on the St. Lawrence promontory (Newfoundland) created a transtensional rift in the Québec re-entrant (Gaspé Peninsula). During the Pridolian, normal block-faulting occurred particularly along the NW-trending eastern margin of the basin where reefs developed on the footwall of the faults. Intra-plate volcanism also occurred from Wenlockian to Emsian along the crustal weakness developed parallel to the NW-trending eastern margin of the basin. Pragian paleogeography shows a deep shelf, carbonate-rich, distal foreland basin in the north, and a siliciclastic turbidite proximal foreland basin developed in front of, and adjacent to, a southern land area. This paleogeographic distribution is compatible with the development of a peripheral foreland basin in front of the Acadian orogenic wedge caused by loading of the Laurentian margin during the convergence of the Avalon terrane within the Québec re-entrant. During the Emsian, the northern deep-shelf carbonates were replaced by littoral and continental sands and gravels reflecting the growing Acadian orogenic wedge to the south and its deep erosion.

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