Geochemistry of Mount Orford ophiolite complex, Northern Appalachians, Canada

Constructional features of the Troodos ophiolite and implications for the distribution of orebodies and the generation of oceanic crust: Discussion

“…The similarity, particularly in rare-earth-element pat-I terns, of the very low-Ti rocks in low-Ti ophiolites to arc boninites would, however, support the suggestion by Pearce et al (1984) that such ophiolites were generated at pre-arc spreading centres located above embryonic subduction zones. As a variation on this theme it has also been suggested (Church 1987) that low-Ti ophiolites (e.g., Harnois and Morency 1988) may have formed in spreading centres originating as transpressive basins in the frontal parts of developing arcs during oblique subduction. In this context the Arakapas fault would represent a transpressive shear along which a locus of spreading had begun to develop involving the intrusion and extrusion of magmas typically showing the crystallization sequence olivine-orthopyroxene-clinopyroxene-plagioclase found in primitive spreading centre ophiolites of the Appalachians (Betts CoveThetford -Mount Orford).…”

Structural evolution of the Thetford Mines Ophiolite Complex, Canada: Implications for the southern Québec ophiolitic belt

“…On the basis of our stratigraphical and structural analysis of the southern Québec ophiolitic belt, complemented by published petrological data [ Laurent , 1975; Laurent et al , 1979; Hébert , 1980, 1983; Beulac , 1982; Oshin and Crocket , 1986; Laurent and Hébert , 1989; Harnois and Morency , 1989; Olive et al , 1997; Hébert and Bédard , 2000; Huot et al , 2002], we present a schematic palinspastic reconstruction of the obducted oceanic terranes in Figure 13. As proposed by Pinet and Tremblay [1995a, 1995b], the southern Québec ophiolites are represented as segments of oceanic crust and mantle formed in a broadly suprasubduction zone setting.…”

Correction to “Structural evolution of the Thetford Mines Ophiolite Complex, Canada: Implications for the southern Quebec ophiolitic belt”

“…The coeval TMOC and AOC, with U/Pb zircon ages of 479 ± 3 Ma and 478-480 +3/À2 Ma, respectively [Dunning et al, 1986;Dunning and Pedersen, 1988;Whitehead et al, 2000], preserve both mantle and crustal rocks, and are dominated by boninitic magmatism (with subordinate tholeiites), a feature which has been attributed to their genesis either in a forearc environment [Laurent and Hébert, 1989;Hébert and Bédard, 2000], and/or in a back arc setting [Oshin and Crocket, 1986;Olive et al, 1997]. In contrast, only the crustal section is present in the MOOC, which contains a greater diversity of magma types, interpreted in terms of arc -back arc [Harnois and Morency, 1989;Laurent and Hébert, 1989;Hébert and Laurent, 1989] or arc-forearc to back arc environments [Huot et al, 2002]. The MOOC has a maximum age of (504 ± 3 Ma [David and Marquis, 1994]).…”

“…Several features make this region an ideal natural laboratory for the elucidation of the complex structural history of a continental margin during oceanic terrane accretion. Specifically: (1) the numerous southern Québec ophiolites are well preserved because they occupy a continental reentrant where the effects of synaccretion tectonism were minimized [e.g., Harris, 1992]; (2) the Devonian (Acadian), postaccretion structural and metamorphic overprint is less severe in southern Québec than in New England [e.g., Tremblay et al, 2000] where critical relations between ophiolites and surrounding rock units are obscured by severe deformation and pervasive, greenschist-to amphibolite-grade metamorphism; (3) most of the southern Québec ophiolites have a near-complete internal stratigraphy (sole, mantle, plutonic rocks, hypabyssal complex, lavas, sediments) and their crystallization ages have been established by U-Pb zircon dating [e.g., Dunning et al, 1986;David and Marquis, 1994;Whitehead et al, 2000]; (4) numerous geochemical studies, including paleotectonic discrimination analyses, are available [Church, 1977[Church, , 1978[Church, , 1987Oshin and Crocket, 1986;Harnois and Morency, 1989;Hébert and Laurent, 1989;Laurent and Hébert, 1989;Olive et al, 1997;Hébert and Bédard, 2000;Huot et al, 2002;Bédard and Kim, 2002]; and finally (5) in southern Québec, the metamorphic and structural evolution of the continental margin is well established [Tremblay and Pinet, 1994;Castonguay and Tremblay, 2003] and constrained by 40 Ar/ 39 Ar isotopic dating [Whitehead et al, 1995;Castonguay et al, 2001;Tremblay and Castonguay, 2002], providing a regional framework for structural analysis of the accreted ophiolites.…”