Timing and spatial distribution of deformation in the Newfoundland Appalachians: a “multi-stage collision” history

Abstract

The Newfoundland Appalachians have been interpreted as an area where Lower Paleozoic plate convergence culminated in collision between an Ordovician volcanic chain and the North American craton in Middle Ordovician times. Closure of the intervening proto-Atlantic (Iapetus) ocean was considered incomplete. Subsequent deformation gave rise to regional folding and faulting. Recent studies in the Newfoundland Dunnage zone have revealed that the deformation history is far more complex than previously recognized. Large-scale thrusting, folding and faulting occurred in Silurian-Devonian times. Furthermore, it has been suggested that the Dunnage zone is an allochthonous terrane underlain by dominantly continental crust rather than representing remnants of a "rooted" ocean basin. In view of these results a revision of tectonic scenarios and zonal subdivision is warranted and a "multi-stage collision" history will be discussed, with emphasis on the spatial distribution and significance of Silurian-Devonian deformation in central Newfoundland. Subduction in Lower Paleozoic times gave rise to the formation of a volcanic terrane; concurrently, to the southeast a marginal sea was formed (Mariana-type subduction). In Middle Ordovician times the volcanic terrane collided with the North American craton ("first-stage collision") and back-arc spreading terminated. Continued crustal shortening resulted in the formation of a Silurian accretionary terrane (telescoped marginal sea), and its subsequent deformation ("second-stage collision"). Devonian (Carboniferous?) strike-slip faulting represents the third stage in the collision history. The model is applicable to large tracts of the Caledonian-Appalachian chain. Its main characteristics are: (a) the revised zonal subdivision of the area is based on characteristics of Silurian and older rocks, rather than Middle Ordovician and older rocks only; (b) the central part of the orogen represents a telescoped marginal sea that formed to the southeast of the Ordovician volcanic chain, rather than a remnant of the incompletely closed Iapetus ocean; (c) the earliest deformation is progressively younger toward the southeast; (d) the Appalachian collision history is a result of the activity of a single deformation regime over a long period of at least 75 Ma.

Paleogeography, accretionary history, and tectonic scenario: A working hypothesis for the Ordovician and Silurian evolution of the northern Appalachians

“…Silurian ages were obtained for regional deformation (e.g., Karlstrom and others, 1982;Colman-Sadd and Swinden, 1984;Chorlton and Dallmeyer, 1986;van der Pluijm, 1986;Currie and Piasecki, 1989;Keppie, 1989;Lafrance, 1989;Elliott and others, 1991;Waldron and Milne, 1991) as well as metamorphic/plutonic activity (Coyle and Strong, 1987;Whalen and others, 1987;Whalen, 1989;Bevier and Whalen, 1990;Dunning and others, 1990). Paleomagnetic and tectonostratigraphic results from north-central Newfoundland that are presented in this paper further demonstrate the significance of Silurian tectonic activity.…”

“…Characteristic tectonic elements in the northern CMB include Lower Paleozoic magmatic arcs, ocean islands, ophiolites, and deep-marine sedimentary sequences as well as early Middle Paleozoic subaerial deposits. The present distribution of these elements and their relationships favor elimination of the previously used Dunnage and Gander two-fold subdivision of the CMB (compare Williams, 1979, with van der Pluijm, 1987, and Williams and others, 1988. The surface boundary between the CMB and the Humber zone is marked by ophiolite assemblages (the Baie Verte-Brompton Line; Williams and St-Julien, 1982).…”

“…2) has received considerable attention, largely because of its excellent coastal exposure. A wealth of stratigraphic (e.g., Kay, 1967;Hibbard and Williams, 1979;Cocks, 1978,1981;Dean, 1978;Kean and others, 1981;Arnott and others, 1985;van der Pluijm and others, 1987), sedimentologie (e.g., Helwig and Sarpi, 1969;Home, 1970;Watson, 1981;Arnott, 1983;Pickering, 1987), geochemical (e.g., Strong, 1977;Strong and Dickson, 1978;Jacobi and Wasowski, 1985;Wasowski and Jacobi, 1985;Swinden and others, 1989;Fyffe and Swinden, 1991), and structural studies (e.g., Helwig, 1967Helwig, , 1970Home, 1969;Kennedy, 1975;Nelson, 1981;Karlstrom and others, 1982;van der Pluijm, 1986;Kusky and others, 1987;Blewett and Pickering, 1988;Elliott and others, 1989;Lafrance, 1989;Williams and Piasecki, 1990) have been carried out in this region. The results presented in this chapter are largely derived from this part of the northern Appalachians.…”

“…Along the orogen, the northern Appalachian segment between Massachusetts and Newfoundland is one of the more interesting examples of collision and terrane accretion processes and consequently has received much attention (e.g., Rast and Skehan, 1983;Zen, 1983;Neuman, 1984;Dunning and Krogh, 1985;Jacobi and Wasowski, 1985;O'Hara and Gromet, 1985;Ludman, 1986;Ayuso, 1986;van der Pluijm, 1987;van Staal, 1987;Williams and Hiscott, 1987;Chandler and others, 1987;Pickering and others, 1988;van der Pluijm and van Staal, 1988;Williams and others, 1988;Zartman, 1988;Boone and Boudette, 1989;Marillier and others, 1989;Stockmal and others, 1990;van Staal and others, 1990;Ayuso and Bevier, 1991). The picture that emerges is one of continent-continent collision between the Laurentian craton and the Avalon terrane, with the latter forming the coastal strip that ranges from eastern Massachusetts (the Boston Basin) to the type area in eastern Newfoundland.…”

“…The Grenvillian basement that underlies the Humber zone outcrops in several places in western Newfoundland, and off-shore deepseismic data indicate that the basement extends a considerable distance under the neighboring Central Mobile Belt (Keen and others, 1986;Marillier and others, 1989). The Central Mobile Belt (CMB) preserves the main remnants of the Iapetus Ocean, and based on structural as well as geophysical grounds the CMB appears to be largely allochthonous (Karlstrom and others, 1982;Karlstrom, 1983;Colman-Sadd and Swinden, 1984;Stockmal and others, 1987;van der Pluijm, 1987;Marillier and others, 1989). Characteristic tectonic elements in the northern CMB include Lower Paleozoic magmatic arcs, ocean islands, ophiolites, and deep-marine sedimentary sequences as well as early Middle Paleozoic subaerial deposits.…”