Anticosti foreland basin offshore of western Newfoundland: Concealed record of northern Appalachian orogen development

Abstract

The Anticosti Basin, largely hidden beneath the Gulf of St. Lawrence, includes foreland basin successions that record multiple tectonic events associated with the Ordovician to Devonian evolution of the northern Appalachian orogen. Due to the lack of well ties and minimal onshore exposure, geophysical data must be used in mapping the offshore stratigraphy. Outcropping geologic boundaries are tied to magnetic lineaments that parallel stratigraphy. These lineaments are correlated with reflections on seismic profiles in order to interpret the subsurface. Seismic isochron maps for successive basin development episodes display differences in geometry, implying that orogenic loading varied through time. The geometry and subsidence rates recorded by the Middle Ordovician Goose Tickle Group imply that it formed in a pro‐arc setting associated with loading during arc‐continent collision that was most intense in the northern Newfoundland Appalachians. The geometry and subsidence recorded by the overlying Long Point Group imply pro‐arc loading by Taconian allochthons in the Québec segment of the orogen. Diachronous subduction polarity reversal along the margin placed the Long Point Group in a combined retro‐arc and pro‐arc setting, comparable to that experienced by parts of the north Australian margin at the present day. The uppermost Silurian to Lower Devonian Clam Bank Formation and Lower Devonian Red Island Road Formation represent foreland basin successions associated with the later Salinian and Acadian orogenies. Their consistent thickness implies a broad, shallow basin, suggesting that the lithosphere was cooler and stronger than during earlier subsidence, and are consistent with a retro‐arc setting.

Terrane history of the Iapetus Ocean as preserved in the northern Appalachians and western Caledonides

“…Regardless of the source of the ophiolites, an off-margin location is also supported by widespread partial melting of the metasedimentary rocks at ~479 Ma (Gerbi et al, 2006b). At this time, sedimentary successions on the outer margin of the Laurentian platform show pelagic facies with no indication of foreland basin development, suggesting that the Chain Lakes block was deformed well before the main Laurentian margin (White et al, 2020;White and Waldron, 2022) (Fig. 4).…”

“…with a large proportion of zircon in the "Grenvillian" 1.0 -1.2 Ga range) throughout their known history. Many of these terranes show evidence of deformation in an Ordovician Taconian series of deformational events widely interpreted as the result of a somewhat diachronous collision of an island arc with the Laurentian margin at a SE-dipping subduction zone, which was followed by a subduction polarity reversal (or "flip") to NW-dipping subduction (Stanley and Ratcliffe, 1985;van Staal et al, 1998;Waldron and van Staal, 2001;White et al, 2020).…”

“…The northern, carbonate-dominated margin of the Australian continent provides a powerful modern analog for Taconian events along the Laurentian margin (e.g. van Staal et al, 1998;White et al, 2020;White and Waldron, 2022). Subduction polarity reversal is progressing westwards along this margin at the present day, converting the Australian margin from passive to active (Fig.…”

“…Maps showing analogy with SE Asia (topography & bathymetry after Amante and Eakins, 2009). (a) Tectonic map of SE Asia and the northern margin of the Australian plate showing effects of arc-continent collision and subduction polarity reversal, and the distribution of ophiolites (Hall, 2002(Hall, , 2012Zahirovic et al, 2014;White et al, 2020;White and Waldron, 2022). (b) Map of Appalachian orogen at similar scale.…”

Accretion, Soft and Hard Collision: Similarities, Differences and an Application from the Newfoundland Appalachian Orogen

“…Ages of diachronous Taconic-Grampian arc-continent collision are indicated in (C). van Staal 2001) and between 470 and 455 Ma in the Quebec reentrant (Tremblay and Pinet 2016;White et al 2020). The hard Taconic collision preserved in the Dashwoods block occurred shortly after an earlier, Late Cambrian-Tremadocian impingement of the LBOT arc with a sediment-rich microcontinent (Dashwoods of Waldron and van Staal 2001) or isolated continental horst (Fig.…”