The St Lawrence Platform and Appalachian deformation front in the St Lawrence Estuary and adjacent areas (Quebec, Canada): structural complexity revealed by magnetic and seismic imaging

Abstract

New magnetic and seismic datasets offer a unique opportunity to document the geometry of the Appalachian front in a poorly studied segment of the orogen. Interpretation of high-resolution magnetic data allows, for the first time, the documentation of the contact between the autochthonous St Lawrence Platform and the Appalachians and highlights the regional significance of previously poorly documented ENE faults that experienced post-Ordovician strike-slip motion. Seismic data reveal tectonic slices in the foreland domain underlying the Appalachians and show that the depth of the décollement at the base of the Appalachian tectonic wedge varies significantly. Taken together, geological, magnetic and seismic data suggest that the geometry of the Appalachian front exhibits significant variations in map and cross-section views and recorded a polyphased structural history.

Upper crustal investigation of the Gulf of Saint Lawrence region, eastern Canada using ambient noise tomography

“…The Humber margin is bounded by a narrow zone of ophiolitic‐ and arc‐related rocks of the NDA [ van Staal et al , ] southeast of the BVBL [ Williams and Julien , ]. The Appalachian Structural Front (ASF) (Figure a) marks the contact between undeformed rocks of the St. Lawrence Platform (SLP) (Figure a) and rocks folded and imbricated during the various orogenic phases that created the Appalachian mountain belt, including the Appalachian structural wedge situated northwest of the BVBL [ Pinet et al , ]. In western Newfoundland, the ASF coincides with the boundary (Logan's Line) between the allochthonous Humber margin and the SLP (Figure ).…”

“…Our tomographic cross sections show that the RIL appears to be steeper in the west (e.g., along A‐A′) than in the east (e.g., along E‐E′). The basement‐cover structure beneath the Humber margin and SLP is more listric on the eastern profiles with the width of the autochthonous SLP, which still overlies its original Grenville basement, varying along strike [ Pinet et al , ]. The relatively lower V s observed at both shallow and midcrustal depths within the Grenville Province (Figures a and e) coincide with prominent low‐gravity anomalies and a characteristic magnetic signature (Figure ) typically associated with known anorthosite suites [ Murthy and Rao , ; Haworth , ; Hayward et al , ].…”

“…In this region, the northern extent of the allochthonous Humber margin and the ASF do not appear to coincide. Rather, the ASF lies further to the north because part of the SLP strata is also involved in the Appalachian structural wedge [ Pinet et al , ]. The Humber margin is bounded by the BVBL to the southeast.…”

“…Further southwest, the ASF is located within a strip of SLP involved in Appalachian deformation [Pinet et al, 2014]. Locally in the GSL, the ASF is truncated at surface by younger sedimentary rocks of the CanMB (Figure 1b), which unconformably overlie the Appalachian structural wedge [Haworth, 1978;Jackson et al, 1998;Pinet et al, 2014]. The middle Paleozoic Gaspé Belt (Figure 1b), found mostly in eastern Quebec and northern New Brunswick, consists of shallow to deep marine clastic sedimentary rocks, volcanic flows, and volcaniclastic rocks [Wilson et al, 2004].…”

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

“…The Île aux Coudres in the Saint Lawrence River, which is part of the Appalachian Humber zone (e.g., Williams ; Lavoie ; Pinet et al. ) and located within the radial limits of the impact structure, is composed of entirely unshocked Neoproterozoic to Cambrian siliciclastic rocks (e.g., Robertson ; Grieve ; Hibbard et al. ).…”