Crustal structure around the margins of the eastern Superior craton, Canada, from receiver function analysis

Abstract

The Precambrian domains of eastern Canada preserve a remarkable record of continental crust formation and evolution spanning at least 3 billion years, and thus present an excellent opportunity to investigate the imprints of early tectonic processes on the present-day continental crust. Archean domains in the region include the eastern Superior craton, part of one of the largest cratons on Earth, the western portion of the North Atlantic craton, and a collage of continental fragments. The Paleoproterozoic Trans-Hudson Orogen and its eastern branches played a fundamental role in the assembly of Laurentia. In the southeast, a succession of orogenic events culminated in the Mesoproterozoic Grenville Orogen and assembly of supercontinent Rodinia. To better understand crustal formation and evolution in this complex region, we use teleseismic P-wave receiver functions recorded by a network of broadband seismographs distributed across Precambrian eastern Canada. At each station, back-azimuthal variations in receiver function waveforms indicate significant lateral crustal heterogeneity, leading us to model different representative directions separately. The stations situated on Archean terranes present a relatively simple crustal structure with a well-defined Moho at ∼33–46 km depth. In contrast, those on Proterozoic domains show a more complex structure, higher velocities in the lower crust and a deeper, more diffuse Moho at ∼46–55 km depth. Across the entire region, bulk crustal composition is largely felsic to intermediate (Vp/Vs ∼1.66–1.76), except for a station situated in an area dominated by anorthosite massifs whose composition is significantly more mafic (Vp/Vs ∼1.85). We combine our new models with those from previous natural- and active-source seismic studies of eastern Canada, and compare our results to those from other Precambrian regions. We suggest that the present-day crustal structure of Precambrian eastern Canada is more strongly influenced by the tectonic processes that assembled Laurentia than secular variations in initial crustal formation.