Taconian orogenesis, sedimentation and magmatism in the southern Quebec-northern Vermont Appalachians: Stratigraphic and detrital mineral record of Iapetan suturing

Abstract

International audienceCambrian-Ordovician units of the southern Quebec Appalachians oceanic domain include obducted ophiolites and an overlying syncollisional sedimentary basin represented by the Saint-Daniel Mélange and flysch units of the Magog Group. These terrains were thrust onto the Laurentian continental margin during the Taconian orogeny and are unconformably overlain by Silurian-Devonian successor basins. This contribution presents and discusses new stratigraphic data acquired in the oceanic domain, as well as U-Pb and 40Ar/39Ar geochronological data on detrital zircons and muscovites sampled at various stratigraphic levels, from the base of the sedimentary units of the oceanic domain and the Silurian-Devonian units of the Gaspé Belt. This work, combined with the compilation of existing data for southern Quebec and western New England allows a better definition of the tectono-stratigraphic evolution of the area, and are used to propose correlations with different rock units of the northern New England Appalachians, which represents a collage of Laurentian margin and oceanic units. It is shown that Cambrian-Ordovician rocks of southern Quebec and northern Vermont have undergone a similar tectonic evolution. The ophiolites were obducted onto the Laurentian margin as a more or less coherent slab of oceanic lithosphere. Both the ophiolites and continental margin rocks were uplifted, eroded and unconformably overlain by Middle to Late Ordovician units of the Saint-Daniel Mélange and Magog Group in a forearc setting. The presence of mafic and felsic volcanic flows that are interstratified within the Saint-Daniel Mélange can be correlated with an episode of delamination and slab breakoff during the final stages of obduction and exhumation of the orogenic wedge. The Magog Group was deposited during the emplacement of the Taconian nappes, as the outboard volcanic arc was still active but progressively shutting down. The provenances suggested by the age of the dated detrital minerals can be entirely reconciled with the peri-Laurentian context of the studied rock units and testify of the tectonic evolution and sedimentary recycling of the Taconian orogen, from ophiolite obduction onto the Laurentian margin, to the collapse of the orogenic belt and the formation of successor basins

In situ U–Pb analysis of shocked zircon from the Charlevoix impact structure, Québec, Canada

“…With respect to the latter, Whitehead et al (1996) demonstrated via 40 Ar/ 39 Ar geochronology that hornblende, muscovite, and K-feldspar crystals in rocks from the Canadian Appalachians in southeastern Qu ebec show thermal signals around~463 Ma related to the Ordovician Taconic orogeny (c. 480-445 Ma; e.g., St. Julien and Hubert 1975;De Souza et al 2014). Tremblay and Castonguay (2002) also reported 40 Ar/ 39 Ar ages of~469-461 Ma, in addition to 40 Ar/ 39 Ar ages of~430-410 Ma, for the domain south of Qu ebec City, reflecting the Salinian orogeny in the Late Silurian and Early Devonian (e.g., Cawood et al 1995;Van Staal et al 2009).…”

Early subduction dynamics recorded by the metamorphic sole of the Mt. Albert ophiolitic complex (Gaspé, Quebec)

“…This suture zone extends along the Appalachians to western Newfoundland, where the Bay of Islands Complex, a klippe of the Dunnage zone, is the most complete ophiolite of the orogeny (Cawood and Suhr, 1992). The Dunnage zone represents the Ordovician oceanic basin related to the Iapetus ocean and located outboard of the continental passive margin of Laurentia defining the Humber zone (Williams, 1979;De Souza et al, 2014). The Mont Albert ophiolite and its sole overlay unconformably the Schick-Schock volcanic flows and pyroclastics metamorphosed to lower greenschist facies that appear in the internal Humber zone in recent publications (reviewed in Tremblay and Pinet, 2016), although Lux (1986) suggested they are part of the Dunnage zone.…”

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

“…No detrital zircon data are available from pre-accretion deposits in these northern Maine inliers, but numerous data sets from the Connecticut Valley -Gaspé trough to the north, and the Central Maine trough to the south, show predominant Laurentia-derived populations (with large peaks at ~0.95 -1.2 Ga) (De Souza et al, 2014;Perrot et al, 2017Perrot et al, , 2018.…”