A tectonic window in central Newfoundland? Geological evidence that the Appalachian Dunnage Zone may be allochthonous

Abstract

In the Through Hill area of central Newfoundland, mafic to ultramafic complexes, which preserve varying amounts of ophiolite stratigraphy, mark the trace of a major fault zone that outcrops in a roughly elliptical pattern. The major, northeasttrending axis is about 60 km and the shorter axis is about 30 km in length. The most complete ophiolite stratigraphy is preserved in the Coy Pond and Pipestone Pond complexes, which have steep dips and face east and west, respectively, outwards from the centre of the ellipse.The ophiolitic rocks are bounded on the outside by rocks typical of the Dunnage Zone of central Newfoundland, principally Lower to Middle Ordovician volcanic and volcaniclastic rocks interpreted to be of island-arc affinity (Davidsville, Victoria Lake, and Baie d'Espoir groups, Cold Spring Pond Formation) and Upper Ordovician to Silurian clastic sediments (Botwood Group). The volcano-sedimentary sequences are interpreted to have been deposited on the ophiolite conformably, but the contacts are not exposed. Both ophiolite and volcano-sedimentary sequences have similar structural and metamorphic histories, exhibiting one principal deformation and the formation of folds with subhorizontal axes, local development of secondgeneration folds and associated cleavage, and an intervening period of metamorphism in the greenschist facies.The elliptical area enclosed by the ophiolite belt is referred to as the Mount Cormack Terrane, and is underlain by variably metamorphosed shale, quartz-rich sandstone, quartzo-feldspathic to amphibolitic gneisses, and granite. A limestone occurrence contains shelly fossils of Early to Middle Ordovician age. An early deformation formed folds with steep axes, and subsequent metamorphism resulted in a progression from greenschist facies to upper amphibolite facies, with the production of migmatite and granodiorite.The preferred interpretation of the geology is that the elliptical Mount Cormack Terrane is exposed as a window through an overlying allochthon composed of ophiolitic and volcano-sedimentary rocks of the Dunnage Zone. The emplacement of the allochthon probably postdated deposition of the Silurian Botwood Group. Paleontologic, lithologic, and structural considerations suggest that the sediments of the Mount Cormack Terrane were deposited at the eastern margin of Iapetus and are perhaps correlatives of rocks exposed in the Gander Zone. This implies that the Dunnage Zone has been thrust, probably in an eastwards direction, on a scale comparable with the allochthons mapped in the Scandinavian Caledonides and proposed for the Appalachians of Quebec and the United States. Dans la region de Through Hill du centre de Terre-Neuve, les complexes mafiques et ultramafiques, dans lesquels sont consemees des sequences ophiolitiques en diverses proportions, marquent la trace d'une zone de faible majeure qui affleure avec un motif plus ou moins elliptique. Le grand axe est orient6 nord-est et s'allonge sur 60 km et le petit axe a une longueur d'environ 30 km. La coupe stratigraphique la plu...

Provenance of tectonic history of the Gander Zone in the Caledonian/Appalachian Orogen: Implications for the origin and assembly of Avalon

“…This Exploits cover is everywhere characterized by the Celtic Fauna (Neuman, 1967(Neuman, , 1984Wonderley and Neuman, 1984). Significant is that this same Exploits cover also unconformably overlies the Early Ordovician ophiolitic rocks of the Exploits Subzone in Newfoundland (Kennedy and McGonigal, 1972;Colman-Sadd and Swinden, 1984) and probably also the Avalon Zone rocks of the Hermitage Flexure in southern Newfoundland (Chorlton, 1978;Dunning and O'Brien, 1989). Hence, the Middle Ordovician Exploits cover was interpreted as an overstep sequence (Williams and Piasecki, 1990; van Staal and Williams, 1991) deposited after early Arenig (Penobscot) obduction of the ophiolites on the Gander clastics, an interpretation confirmed through dating a stitching pluton (Partridgeberry Hills Granite: 474 +6/-3 Ma) by .…”

“…1) lies in northeastern Newfoundland near the town of Gander (Kennedy and McGonigal, 1972;Kennedy, 1976). Regional mapping subsequently showed that the distinct clastic rocks of the Gander area could be extrapolated into southern and southwestern Newfoundland (Brown and Colman-Sadd, 1976;Williams, 1979;Colman-Sadd, 1980) and into structural basement windows in the Exploits Subzone of the Dunnage Zone of central Newfoundland (Colman-Sadd and Swinden, 1984;Williams et al, 1988). Detrital titanite and intrusive granites show that the Gander rocks are younger than ca.…”

Tectonic implications of early silurian thrust imbrication of the northern exploits subzone, Central Newfoundland

“…Post-Middle Ordovician thrust faults were also reported from the Exploits Subzone by Kay and Williams (1963), Jacobi and Schweickert (1976) Kidd (1977) Blackwood (1979Blackwood ( , 1982, Pajari er al. (1979), Colman-Sadd (1980), Thurlow (1981), Colman-Sadd and Swinden (1984), van der Pluijm, (1984van der Pluijm, ( , 1986van der Pluijm, ( ,1987. van der Pluijm and van Staal(1988) Kusky (1985) Kusky and Kidd (1985), Elliott (1985a); and Elliott and Williams (1988).…”

A new species of stalked crinoid (Echinodermata) of possible Late Silurian age from central Newfoundland

“…Trilobite, brachiopod and graptolite localities have received most attention, and precise stratigraphic data generally in dicating Early and Middle Ordovician ages have been ob tained (e.g., Colman-Sadd and Swinden, 1984;Boyce, 1987;Boyce eta l., 1988Boyce eta l., , 1993aWilliams, 1991Williams, , 1993Williams et al, 1992). Localities containing mainly cririoids, bryozoa, and corals and a few brachiopods have only rarely been ex amined in detail.…”