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

Abstract

We studied the 3‐D shear wave velocity (Vs) structure in the Gulf of St. Lawrence (GSL) and adjacent onshore areas to 20 km depth by inverting Rayleigh wave dispersion extracted from the vertical components of continuous ambient seismic noise waveforms. The region is divided into three broad zones based on their Vs characteristics. In the northwest, the Grenville Province (i.e., the exposed edge of predominantly Middle‐Proterozoic Laurentian crust) is dominated by high Vs, except for well‐known anorthosite sites, which are characterized by relatively lower Vs. In contrast, the central segment of the GSL region corresponds to a belt with generally low Vs at upper crustal levels. In the southeastern part of the GSL, prominent low Vs in the uppermost crust are found to coincide with locations of subsidiary basins of the Canadian Maritime Basin, while higher Vs characterize the accreted Appalachian terranes where they are exposed on land. The Grenville Province is wedged out at depth by the Red Indian Line, which is the suture between composite Laurentia and peri‐Godwanan Ganderia in the Canadian Appalachians. The geometry and Vs characteristics of the south‐easternmost peri‐Gondwanan terranes of Avalonia and Meguma suggest that they may be fully or partially structurally overlying a basement with distinct seismic characteristics, which could be a vestige of the West African craton that was underthrust beneath composite Laurentia during the terminal Alleghenian continent‐continent collision. In the middle of the GSL, the 3‐D geometry of the Canadian Maritimes sedimentary basins overlying the Appalachian terranes shows that the depth to the top of basement is in excess of 8 km.

Crustal Structure Beneath the Northern Appalachians and the Eastern Grenville Province

“…This sedimentary basin has a U‐shaped geometry with the maximum thickness located beneath PEI. Our interpretations are consistent with the previous ANT study carried out over the GSL (Kuponiyi et al., 2017). The next thickest sedimentary layer is located under the NE St. Lawrence River and beneath the Humber margin with a thickness of ∼5–6 km.…”

“…The Gulf of St. Lawrence at depths $$< $$20 km is dominated by slow anomalies (Kao et al., 2013). A regional‐scale study carried out over this area suggests a maximum sedimentary thickness of ∼8 km beneath this region (Kuponiyi et al., 2017). It is also suggested that the Grenvillian basement beneath the northern Appalachians is wedged out at depth by the Red Indian Line (Kuponiyi et al., 2017).…”

“…A regional‐scale study carried out over this area suggests a maximum sedimentary thickness of ∼8 km beneath this region (Kuponiyi et al., 2017). It is also suggested that the Grenvillian basement beneath the northern Appalachians is wedged out at depth by the Red Indian Line (Kuponiyi et al., 2017). Adopting a probabilistic joint‐inversion scheme, Shen and Ritzwoller (2016) used receiver functions, group, and phase velocities from ambient noise and earthquakes, and Rayleigh wave ellipticity measurements, and obtained high resolution shear velocity models at crustal and uppermost mantle depths across the entire USA.…”

“…To this end, seismic tomography models are extremely valuable as they can provide us with a detailed look at the velocity structure at different scales. With the aim of obtaining high resolution tomographic images of the crust and sub‐Moho structure beneath southeastern Canada and the NE United States, we used recent records of broadband seismic data in a passive seismic technique, namely Ambient Noise Tomography (ANT; Shapiro & Campillo, 2004; Shapiro et al., 2005), that has been successful in recovering detailed crustal and uppermost mantle velocity structure in regional‐scale (e.g., Green et al., 2017; Kuponiyi et al., 2017; Lin et al., 2008; McLellan et al., 2018; Pawlak et al., 2012; Y. Yang et al., 2008) and continental scale (e.g., Bensen et al., 2008; Kao et al., 2013; Y. Yang et al., 2007) studies. Recently added data coverage in our study area, in the years from 2013 to 2015, provides us with an unprecedented opportunity to recover the highest resolution anisotropic velocity structure of the crust and sub‐Moho depths to date.…”

Lithospheric Structure and Flat‐Slab Subduction in the Northern Appalachians: Evidence From Rayleigh Wave Tomography

“…A northwest‐dipping fabric at lower crust to mantle depths is imaged in central Newfoundland that likely indicates a relict subduction zone (e.g., van der Velden et al., 2004). Further west, upper‐ to mid‐crustal depths beneath the Gulf of Saint Lawrence were studied using a surface wave tomography method, and westward dipping of Avalonia beneath Ganderia was interpreted (Kuponiyi et al., 2017). Continental‐scale seismic tomography models at crustal depths show an overall decrease of seismic velocities from the eastern Grenville to the northern Appalachians but lack enough resolution to provide more detailed tectonic interpretations (e.g., Kao et al., 2013).…”