Proterozoic orogens of the northeastern Canadian Shield: new information from the Lithoprobe ECSOOT crustal reflection seismic survey

Abstract

As part of the Eastern Canadian Shield Onshore–Offshore Transect (ECSOOT), Lithoprobe acquired 1250 km of deep seismic reflection data along the coast of Labrador and across Ungava Bay, to image evidence of Proterozoic crustal accretion to the Archean nuclei of the Nain and Superior provinces of the Canadian Shield. The relatively pristine Archean crust of the Nain Province has low reflectivity and generally lacks systematic reflector orientations. Reworking of Archean crust on the margins of the Makkovik Province has little effect on this weak signature. In contrast, the Archean crust in the Eastern Churchill (Rae) Province appears to have been overprinted by a strongly developed, whole-crustal, easterly dipping reflection fabric, interpreted to result from Proterozoic collision of the Nain and Superior provinces in the paired New Quebec and Torngat orogens. Juvenile Proterozoic crust in the Makkovik and Grenville provinces also shows strong whole-crustal dipping reflection fabrics, interpretable as outwardly verging structures associated with collisional mobile belts. Crustal thickness varies from 35 to 45 km in Proterozoic provinces, except where thinner in areas probably affected by Mesozoic extension associated with rifting of the Labrador Sea. Dipping reflectors in the mantle are commonly associated with strong lower-crustal dipping reflections in a manner similar to that observed in some modern orogens. The ECSOOT data show that Proterozoic crust in this area has structural forms comparable with those of modern orogens and, inferentially, its tectonic development was controlled by very similar collisional processes.

Crustal structure and gravity field anomalies in Eastern Canada /

“…Northern ECSOOT seismic line across Ungava Bay (Hall et al, 1995) 129 Martignole and Pouget (1993; and location of Lithoprobe seismic line 52. The gravity data were projected on the profile represented by the discontinuous line.…”

“…The gravity data were projected on the profile represented by the discontinuous line. BSZ is the Baskatong shear zone 33 Wardle et al (1990) and Hall et al (1995) . b) Profile P2 running from 290°E to 295°E at 58.5°N.…”

“…Elles permettent de corréler les structures géologiques identifiées sur le continent avec les images de la croûte fournies le long du profil de sismique marine à travers la baie d'Ungava (Hall et al, 1995). Il n'y a pas eu de mesures de gravité dans la baie d'Ungava.…”

“…1). The seismic transects image structures related to the formation of Archean crust and the successive accretion of Proterozoic terranes (Hall et al, 1995).…”

Evolution of migmatitic granulite complexes: Implications from Lapland Granulite Belt, Part I: Metamorphic geology

“…The geological history of the LGB also has a key role in the interplate correlation of ca. 1.8−2.0 Ga orogenic events between the Canadian and Fennoscandian Shields (Gaál & Gorbatschev, 1987;Hoffman, 1988Hoffman, , 1989Bridgwater et al, 1990;Hall et al, 1995).…”