A ⁴⁰Ar/³⁹Ar study of oceanic and continental deformation processes during an oblique collision: Taconian orogeny in the Quebec reentrant of the Canadian Appalachians

Abstract

Two phases of penetrative deformation are documented in the Taconian hinterland of the Appalachian orogen in the Gaspé Peninsula. D1 is associated with the obduction of the Mont‐Albert ophiolite onto the Paleozoic Laurentian margin, whereas D2 corresponds to later transport of allochthons across the margin. In the metamorphic sole, S1 is a SE‐dipping mylonitic fabric with a downdip lineation. In underlying metabasalts, D1 is characterized by NW‐overturned and recumbent folds, and a subhorizontal S1 schistosity with an ENE‐trending orogen‐parallel lineation. D2 is characterized by a S2 steeply dipping penetrative axial‐planar crenulation cleavage and NE‐trending F2 folds. The intraoceanic thrusting of ophiolite is dated at 465 Ma (early D1) whereas emplacement of ophiolite and subsequent deformation of the margin was recorded by isotopic signatures between 459 and 456 Ma (late D1). D2 is dated at 448 Ma throughout the hinterland. Taconian transpressive deformation is related to an oblique collision within the Quebec reentrant of the Canadian Appalachians during the Ordovician.

Hinterland-directed transtensional faulting at an orogen structural front: The example of the Cap-Chat melange, Quebec Appalachians

“…9). As noted by Malo et al (2008), D 1 deformation in the external Humber zone is in part contemporaneous with geochronologically constrained late deformation and metamorphism in the internal Humber zone (Fig. 9).…”

“…The Shickshock Group is structurally overlain by the Mont-Albert ophiolitic complex, which forms part of the Dunnage zone of Williams (1979). Geochronologic data (Pincivy et al, 2003;Malo et al, 2008) bracket ophiolite accretion on the margin as well as the metamorphism of underlying rocks to Late Ordovician time (454)(455)(456)(457)(458)(459). To the SE, the Humber and Dunnage zones either are unconformably overlain by, or are in fault contact with Upper Ordovician to Middle Devonian rocks that form the Gaspé belt ( Fig.…”

“…The Taconian stage (Late Ordovician) involved obduction of ophiolitic material onto the Laurentian continental margin (Malo et al, 2008) and the associated stacking of NWdirected thrust nappes. In the Cap-Chat mélange, F 1 folds are characterized by tighter hinge zones than are usual in the external Humber zone.…”

Structure, geochemistry, and tectonic evolution of trench-distal backarc oceanic crust in the western Norwegian Caledonides, Solund-Stavfjord ophiolite (Norway)

“…This time span is largely consistent with the formation and the subsequent tectonic accretion of ophiolites and arc-backarc complexes (5-10 m.y.) in the Canadian Appalachians during the Taconic orogeny (Lissenberg et al, 2005;Malo et al, 2008), as well as with the inferred time brackets of the Tethyan marginal basins (Dilek et al, 1999;Dilek and Moores, 1990;Dilek et al, 2007Dilek et al, , 2008.…”

Revisiting the Appalachian structural front and offshore Anticosti Basin (northern Gulf of St. Lawrence, Canada) by integrating old and new geophysical datasets

“…This interpretation is based on radiochronologic data in the metamorphic internal domain (Pincivy et al, 2003;Malo et al, 2008), on the age of syn-tectonic flysch sedimentation (Hiscott, 1984(Hiscott, , 1995 and on structural observations attesting to significant pre-Silurian deformation (St-Julien and Hubert, 1975). Major structural features in the area bounding the St. Lawrence River were interpreted to belong to a typical north-directed foreland fold-and-thrust belt (St-Julien and Hubert, 1975).…”