Crustal Structure Beneath the Northern Appalachians and the Eastern
Grenville Province
Abstract
Southeastern Canada and the northeastern USA include terranes that were
tectonized since the Archean, making this region an excellent place to
investigate the evolution of continental crust. Our study area covers
the Archean southeastern Superior Province, the Proterozoic eastern
Grenville, and the Phanerozoic northern Appalachians comprising terranes
with either Peri-Laurentian or Peri-Gondwanan heritage. Adopting a
Rayleigh wave ambient noise tomography method, we used noise data
recorded between 2013 and 2015, and obtained high resolution anisotropic
tomographic images of the crust enabling us to discuss tectonic
implications. The azimuthal anisotropy orientations follow a dominant
NE-SW trend across the study area, but some localized changes of
anisotropy direction in the Bay of Fundy and across the Appalachian
front are observed. The crust beneath the older Superior and Grenville
provinces is generally fast, whereas the Appalachians include strong
slow anomalies, especially at upper crustal depths, where they represent
thick sedimentary basins beneath the St. Lawrence valley, the Gulf of
St. Lawrence and the Bay of Fundy. We suggest that the boundary between
the Peri-Laurentian and the Peri-Gondwanan terranes at depth is marked
by a Moho-offset feature observable in our models. A generally similar
crustal seismic signature for the youngest two easternmost tectonic
domains suggest that they were never separated by a wide ocean basin.
Our results provide important evidence for evolution of the continental
crust during and after accretionary/collisional episodes in the study
area.