Alleghanian deformation in the eastern Gaspe Peninsula of Quebec, Canada Pierre Jutras² Department of Geology, Saint Mary's University, Halifax, Nova Scotia B3H 3C3, Canada Gilbert Prichonnet GEOTERAP, DeÂpartement des Sciences de la Terre et de l'AtmospheÁre, Universite du Quebec aÁ MontreÂal, C.P. 8888, Succursale Centre-Ville, MontreÂal, Quebec H3C 3P8, Canada Steven McCutcheon New Brunswick Department of Natural Resources and Energy, P.O. Box 50, Bathurst, New Brunswick E2A 3Z1, Canada ABSTRACT sin, Cannes-de-Roches Basin, Carbonifer- rocks of the Gaspe Peninsula. We argue herein ous, strike-slip faults. that these structures are related to the Allegh- Juxtaposition of the Mississippian Risti- anian orogeny and were responsible for the INTRODUCTION gouche and Cannes-de-Roches Basins, postsedimentary juxtaposition of two Missis- sippian depocenters, namely, the Ristigouche which are subbasins of the composite late Transpressive deformations associated with (van de Poll, 1995) and Cannes-de-Roches Paleozoic Maritimes Basin, occurred peripheral effects of the Carboniferous to (Jutras et al., 2001) Basins (Fig. 1). These de- through dextral movement along the north- Permian Alleghanian orogeny are well docu- pocenters are subbasins of the large late Pa- west-striking Perce Fault system in the east- mented in Atlantic Canada (Fralick and leozoic Maritimes Basin, which extends ern Gaspe Peninsula of Quebec. The north- Schenk, 1981; PiqueÂ, 1981; Bradley, 1982; throughout most of Atlantic Canada (Fig. 1A). west-striking faults are truncated by small Keppie, 1982; Ruitenberg and McCutcheon, Identi®cation of post-Acadian transpressive north-northwest±striking dextral strike-slip 1982; Nance and Warner, 1986; Gibling et al., faults, which probably developed as region- 1987, 2002; McCutcheon and Robinson, structures in the Gaspe Peninsula indicates al stress gradually rotated clockwise from 1987; Nance, 1987; Yeo and Ruixiang, 1987; that the tectonic impact of the Alleghanian north-northwest±south-southeast to north- Reed et al., 1993; Murphy et al., 1995; Pas- orogeny affected rocks much farther north east-southwest. This study provides the ®rst cucci et al., 2000). However, until now, it was than previously thought, thus adding signi®- evidence in eastern Quebec for signi®cant thought that the Alleghanian fault system that cantly to our understanding of late Paleozoic post-Acadian block displacement other affects Carboniferous rocks of the Maritime tectonics in the northern Appalachians. The than normal faulting and indicates that Al- Provinces did not extend as far north as the identi®cation also underlines a need to re- leghanian deformation extended much far- Gaspe Peninsula of Quebec (Fig. 1), a large evaluate the age attribution of all brittle strike- ther north than previously thought. Iden- segment of the Canadian Appalachians. Prior slip faults in the Gaspe Peninsula, which were ti®cation of these structures formed during to a study by Faure et al. (1996a), post-Acadian previously attributed to late stages of the Aca- the Alleghanian orogeny but more than deformation in the rocks of the Gaspe Penin- dian orogeny (Kirkwood et al., 1995; Malo 1000 km away from areas of peak Allegh- sula was thought to be limited to Carbonifer- and Kirkwood, 1995). anian metamorphism in the southeastern ous synsedimentary dip-slip faulting (Rust et United States underlines the far-reaching al., 1989) and to minor postsedimentary nor- POST-ACADIAN TECTONIC HISTORY effects of continental collisions. It also casts mal-fault readjustments (Alcock, 1935; St- OF SOUTHEASTERN CANADA doubt on the age attribution of brittle Julien and Hubert, 1975; Bernard and St- strike-slip faults elsewhere in the Gaspe Julien, 1986; Kirkwood, 1989; Bourque et al., The Middle Devonian Acadian orogeny Peninsula, away from Mississippian expo- 1993; Peulvast et al., 1996). Faure et al. brought together Laurentia, Baltica, and sures. Such brittle faults were previously (1996a) documented evidence for post- Gondwana, and during Late Devonian and associated with late stages of the Acadian Acadian compressive paleostresses from slick- Mississippian time, southeastern Canada orogeny but could in fact be considerably en®bers on mesoscopic brittle fault planes in mainly was subjected to extension and graben younger. southern Quebec, including the Gaspe Penin- formation (Howie and Barss, 1975; Arthaud sula, but no signi®cant displacement was and MatteÂ, 1977; Fralick and Schenk, 1981; noted. Bradley, 1982; Keppie, 1982, 1993; Ruiten- Keywords: Alleghanian orogeny, structural Described here are large transcurrent faults berg and McCutcheon, 1982; Fyffe and Barr, geology, Gaspe Peninsula, Ristigouche Ba- and associated compressive features, such as 1986; Gibling et al., 1987, 2002; McCutcheon reverse faults and drag folds, which were rec- and Robinson, 1987; Rust et al., 1989; Pe-Piper ²E-mail: [email protected]. ognized for the ®rst time in Mississippian et al., 1991; Durling and Marillier, 1993; Reed GSA Bulletin; December 2003; v. 115; no. 12; p. 000±000; 13 ®gures; Data Repository item 2003xxx. For permission to copy, contact [email protected] q 2003 Geological Society of America ALLEGHANIAN DEFORMATION IN EASTERN GASP&a PENINSULA, QUEBEC Figure 1. (A) Location of the study area within the late Paleozoic Maritimes Basin (light shading where its deposits are currently below sea level and dark shading where they are on land; modi®ed from Gibling et al., 1992). (B) Simpli®ed geology of the eastern Gaspe Peninsula (modi®ed from Brisebois et al., 1992), showing only post-Acadian (Middle Devonian) relationships. Box in the vicinity of Mal Bay shows map area of Figure 3. et al., 1993; Murphy et al., 1995; Pascucci et al., 2000). Onset of this extension was coeval with orogenic uplift in New England, source area of the uppermost Devonian Catskill clas- tic wedge (Rust et al., 1989). Within the Low- er to Middle Devonian clastic wedge of the eastern Gaspe Peninsula, observation of a gradual displacement of source areas from the southeast to the southwest led Rust et al. (1989) to propose a model that correlates this succession with the Upper Devonian Catskill clastic wedge within one continuous wrench tectonic event. This Devonian migration of stress and foreland-basin development toward the southwest was accommodated by the grad- ual closing of the Theic (or ``Rheic'', for some authors) Ocean (Fig. 2A), which culminated with the Pennsylvanian to Early Permian Al- leghanian orogeny and the formation of Pan- Figure 2. Tectonic model for the formation and deformation of the Maritimes Basin in gea (Fig. 2B) (Arthaud and MatteÂ, 1977; Pi- the context of Theic Ocean closure. Dotted line represents the contour of the Precambrian queÂ, 1981; Lefort and van der Voo, 1981; West African craton within Gondwana. Light wavy lines represent areas affected by pen- Russell and Smythe, 1983; Haszeldine, 1984; etrative early to middle Paleozoic (pre±Late Devonian) deformation. Thick wavy lines Kent and Opdyke, 1985; Lefort et al., 1988; represent areas that were then affected by penetrative deformation. Dark gray shading Kent and Keppie, 1988; Rodgers, 1988; Sacks represents areas of active continental clastic sedimentation; white arrows represent in- and Secor, 1990; Pique and Skehan, 1992; ferred paleocurrent trends. Keppie, 1993; Faure et al., 1996a). As the West African craton converged with southern North America (Lefort and van der have accommodated much of these plate re- Roches Basins of eastern Quebec are among Voo, 1981; Sacks and Secor, 1990; Pique and adjustments, generating pull-apart extension the grabens that developed in southeastern Skehan, 1992), Gondwana rotated counter- in most of southeastern Canada as the main Canada during the Late Devonian and the clockwise with respect to the assembled Eur- stress vectors migrated toward New England Mississippian; altogether the grabens formed american landmass (Laurussia), causing dex- (Fig. 2A). In favor of the pull-apart model, the composite Maritimes Basin (Fig. 2A). tral shear from central Europe to northeastern Late Devonian and Mississippian magmatism The Reguibat uplift, a well-de®ned prom- North America (Kent and Keppie, 1988) (Fig. along the Cobequid-Chedabucto Fault evolved ontory on the West African craton margin, act- 2A). Within this general context, the Cobequid- under a transpressive regime (Koukouvelas et ed as a rigid indenter when Gondwana and Chedabucto Fault, which separates a Gond- al., 2002), while the rest of southeastern Can- southeastern North America started colliding wanan terrane (Meguma) from Iapetan ter- ada was undergoing general extension. The in Pennsylvanian time, and much of the com- ranes in Nova Scotia (Keppie, 1982), may Mississippian Ristigouche and Cannes-de- pression concentrated around it (Lefort and Geological Society of America Bulletin, December 2003 JUTRAS et al. van der Voo, 1981; Sacks and Secor, 1990; Gaspe Peninsula, whether ductile or brittle, (Rust, 1981). These units are now absent from Pique and Skehan, 1992; Faure et al., 1996a) were assigned to late stages of the Acadian the inferred source area for the Bonaventure (Fig. 2B). Peripheral areas, such as the Mari- orogeny (Malo and BeÂland, 1989; Malo et al., Formation detritus in the Cannes-de-Roches times Basin, mainly were subjected to tran- 1992, 1995; Kirkwood et al., 1995; Malo and Cove section, which is to the southwest ac- spressive accommodation of this indentation, Kirkwood, 1995) and had not been