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A lost arc–back-arc terrane of the Dunnage oceanic tract recorded in clasts from the Garin Formation and McCrea mélange in the Gaspé Appalachians of Québec

Céline Dupuis^1,, Michel Malo^1,*, Jean Bédard^2,, Bill Davis³ and Mike Villeneuve³

¹ Institut National de la Recherche Scientifique, Eau, Terre et Environnement, 490 de la Couronne, Québec, Québec G1K 9A9, Canada
² Geological Survey of Canada–Québec, Earth Science Sector, 490 de la Couronne, Québec, Québec G1K 9A9, Canada
³ Geological Survey of Canada–Ottawa, Earth Science Sector, 601 Booth Street, Ottawa, Ontario K1A 0E8, Canada

View larger version (38K): [in this window] [in a new window]   Figure 1. Location map showing the Gaspé Peninsula of southern Quebec, New Brunswick, northern Maine and adjacent areas (after Winchester and van Staal, 1994). BBL—Baie Verte–Brompton Line; RIL—Red Indian Line.

View larger version (77K): [in this window] [in a new window]   Figure 2. Generalized geology of Gaspé and northern central New Brunswick (modified after Malo, 2004; Gosselin, 1988 [inset]; van Staal et al., 2003; Wilson et al., 2004). Xs on inset map indicate sampling locations. BBL—Baie Verte–Brompton Line; LSC—Lady Step Complex; McG—Mictaw Group; MqG—Maquereau Group; NOM—Nadeau ophiolitic mélange; RPDM—Rivière Port-Daniel mélange. Numbers 1–5 and letters A–D correspond to locations of stratigraphic sections of Figure 3.

View larger version (45K): [in this window] [in a new window]   Figure 3. Biostratigraphical position and correlation of the rock units (modified from Malo, 2004; Wilson et al., 2004; van Staal et al., 2003). CB+MC—Corner of the Beach and Murphy Creek Formations; F—felsic rocks; Fm—Formation; Gr—Group; Ll—Llanvirnian; M—mafic rocks. Numbers and letters in column headings correspond to locations shown in Figure 2. Radiometric ages are from Webby et al. (2004).

View larger version (34K): [in this window] [in a new window]   Figure 4. Geological map of the McCrea inlier south of the Grand Pabos fault (modified from Malo et al., 1992b). PS—Pabos Suite; sp—serpentinite; v + g—volcanic and granitic rocks.

View larger version (16K): [in this window] [in a new window]   Figure 5. Zr/Ti versus Nb/Y classification diagram of Winchester and Floyd (1977).

View larger version (36K): [in this window] [in a new window]   Figure 6. Nb-Y discrimination diagram for intermediat-felsic rocks (after Pearce et al., 1984). Gray fields represent rocks of the Exploits subzone from different regions of New Brunswick and northern Maine, as well as rocks of the Notre Dame subzone in the Gaspé Peninsula (Québec) and Newfoundland: (A) Pabos Suite and McCrea mélange, the Gaspé Peninsula, Québec (Malo et al., 1992b); (B) Tetagouche and California Lake Groups, in the northern Miramichi Highlands (light gray; van Staal et al., 1991; Rogers et al., 2003b), and Goulette Brook Formation in the Popelogan inlier (dark gray; Wilson, 2003), northern New Brunswick; (C) Meductic Group in the southern Miramichi Highlands, southern New Brunswick (Dostal, 1989; Fyffe, 2001); (D) Winterville Formation and Stacyville volcanics in the Winterville, Munsungun, Castle Hill, and Weeksboro-Lunksoos (W-L) inliers, northern Maine (Winchester and van Staal, 1994; Schulz and Ayuso, 2003); and (E) Red Indian Lake Group (RIL Gr.) (light gray) and Otter Pond complex intrusions (dark gray) in the Annieopsquotch accretionary tract, Newfoundland (Lissenberg et al., 2005b; Zagorevski et al., 2006).

View larger version (27K): [in this window] [in a new window]   Figure 7. Classification of mafic-intermediate and tholeiitic-to-alkaline suite cobbles in the La-Y-Nb discrimination diagram of Cabanis and Lecolle (1989). Gray fields represent mafic to intermediate rocks of the Exploits subzone from different regions of New Brunswick and northern Maine, as well as rocks of the Notre Dame subzone in the Gaspé Peninsula (Quebec) and Newfoundland: (A) Pabos Suite (dark gray) and McCrea mélange (light gray), Gaspé Peninsula, Quebec (Bédard, 1986; Malo et al., 1992b); (B) Fournier, Tetagouche, and California Lake Groups in the northern Miramichi Highlands (van Staal et al., 1991; Winchester et al., 1992; Rogers et al., 2003b), northern New Brunswick; (C) Meductic Group in the southern Miramichi Highlands, southern New Brunswick (Dostal, 1989; Fyffe, 2001); (D) Winterville Formation and Stacyville volcanics in the Winterville, Munsungun, Castle Hill, and Weeksboro-Lunksoos (W-L) inliers, northern Maine (Winchester and van Staal, 1994; Schulz and Ayuso, 2003); and (E) Red Indian Lake Group (Harbour Round Formation [HR]) (light gray) and Otter Pond complex intrusions (dark gray) in the Annieopsquotch accretionary tract, Newfoundland (Lissenberg et al., 2005b; Zagorevski et al., 2006). Key: BABB—back-arc basin basalt; CAB—calc-alkaline basalt; CB—continental arc basalt; IAT—island-arc tholeiite; MORB—mid-ocean-ridge basalt (N-MORB—normal MORB, E-MORB—enriched MORB); OIB—ocean-island basalt.

View larger version (43K): [in this window] [in a new window]   Figure 8. Multi-element patterns normalized to primitive mantle (PM) for the three Garin rock suites. Normalizing values in this and subsequent figures are from Sun and McDonough (1989). CAIF—calc-alkaline intermediat-felsic, TA—tholeiitic-to-alkaline suite, MI—mafic-intermediate.

View larger version (17K): [in this window] [in a new window]   Figure 9. 39Ar-40Ar age data for hornblende from the gabbronorite of the Pabos Suite. (A) 39Ar-40Ar gas release plot. Steps included in plateau age are marked by dashed line terminated by arrowheads. (B) Inverse isochron plot indicating presence of excess 40Ar. Steps containing less than 1% of 39Ar released are grayed and not included in regression.

View larger version (20K): [in this window] [in a new window]   Figure 10. U-Pb zircon concordia diagrams for new age determinations from igneous clasts of the Garin Formation: (A) monzonite RJ-27, and (B) porphyritic rhyodacite/dacite RLH-87.

View larger version (30K): [in this window] [in a new window]   Figure 11. (A–B) Middle Ordovician tectonic evolution of the Dunnage oceanic tract (Exploits subzone) in Gaspé, New Brunswick, and northern Maine (modified after van Staal et al., 2003): (A) calc-alkaline magmatism of the Popelogan arc; and (B) rifting and opening of the Tetagouch-exploits back-arc basin. (C) Middle Ordovician tectonic evolution of the Annieopsquotch accretionary tract (Notre Dame subzone) (modified after Zagorevski et al., 2006): rifting of the remnant Buchans arc and formation of the new active Red Indian Lake arc. Annieopsquotch ophiolite belt (AOB) and Lloyds River ophiolite complex (LROC) are already accreted on the Dashwoods microcontinent.

View larger version (47K): [in this window] [in a new window]   Figure 12. Multi-element patterns normalized to primitive mantle (PM) for heavy rare earth element (HREE)–poor rocks of the calc-alkaline intermediat-felsic (CAIF) suite. Gray fields outline compositional range of intermediate to felsic rocks of the Dunnage zone from different regions of New Brunswick, northern Maine, and Newfoundland (complete references are given in the caption of Fig. 6).

View larger version (54K): [in this window] [in a new window]   Figure 13. Multi-element patterns normalized to primitive mantle (PM) for heavy rare earth element (HREE)–rich rocks of the calc-alkaline intermediat-felsic (CAIF) suite. Gray fields outline compositional range of intermediate to felsic rocks of the Dunnage zone from different regions of the Gaspé Peninsula (Quebec), New Brunswick, and northern Maine (complete references are given in the caption of Fig. 6).

View larger version (54K): [in this window] [in a new window]   Figure 14. Multi-element patterns normalized to primitive mantle (PM) for the volcanic rocks of the Miguasha-Est no. 1 well. Gray fields outline the same compositional range as that of Figure 13.

View larger version (31K): [in this window] [in a new window]   Figure 15. Multi-element patterns normalized to primitive mantle (PM) for the tholeiitic-to-alkaline suite (TA). Normalizing values are from Sun and McDonough (1989). Gray fields outline compositional range of mafic rocks of the Dunnage zone from different regions in New Brunswick and northern Maine (complete references are given in the caption of Fig. 7).

View larger version (50K): [in this window] [in a new window]   Figure 16. Multi-element patterns normalized to primitive mantle (PM) for basalts of the mafic-intermediate (MI) suite. Gray fields outline compositional range of mafic rocks of the Dunnage zone from different regions of the Gaspé Peninsula (Quebec), New Brunswick, northern Maine, and Newfoundland (complete references are given in the caption of Fig. 7).

View larger version (50K): [in this window] [in a new window]   Figure 17. Multi-element patterns normalized to primitive mantle (PM) for basaltic to andesitic rocks of the mafic-intermediate (MI) suite. Gray fields outline compositional range of mafic to intermediate rocks of the Dunnage zone from different regions of the Gaspé Peninsula (Quebec), New Brunswick, northern Maine, and Newfoundland (complete references are given in the caption of Fig. 7).