Crustal structure of the Grenville Province in southeastern Labrador from refraction seismic data; evidence for a high-velocity lower crustal wedge

• Published in: Canadian journal of earth sciences Vol. 38; no. 10; pp. 1463 - 1478
• Main Authors: Funck, Thomas, Louden, Keith E, Reid, Ian D
• Format: Journal Article
• Language: English
• Published: Ottawa, Canada National Research Council of Canada 01.10.2001; NRC Research Press; Canadian Science Publishing NRC Research Press
• Subjects: applied (geophysical surveys & methods); Atlantic Ocean; body waves; Canada; Canadian Shield; continental margin; crust; crustal thickening; dikes; Eastern Canada; Eastern Canadian Shield Onshore-Offshore Transect; ECSOOT; elastic waves; Geology; geophysical methods; geophysical profiles; geophysical surveys; Geophysics; Grenville Front; Grenville Province; high-velocity zones; intrusions; Labrador; Lithoprobe; lower crust; Makkovik Province; Newfoundland; Newfoundland and Labrador; North America; North Atlantic; Northwest Atlantic; P-waves; refraction methods; seismic methods; seismic profiles; seismic waves; Seismology; solid Earth (tectonophysics); southeastern Labrador; surveys; underplating; velocity structure; Wave velocity; Canada; Grenville Ontario Canada; Labrador Newfoundland & Labrador Canada; Newfoundland & Labrador Canada; Canada, Canadian Shield, Grenville Province
• ISSN: 0008-4077; 1480-3313
• DOI: 10.1139/e01-026

The crustal structure of the eastern Grenville and Makkovik provinces was determined using two onshore-offshore refraction seismic lines of the Lithoprobe Eastern Canadian Shield Onshore-Offshore Transect (ECSOOT). A gravity high in the Hawke River terrane correlates with increased P-wave velocities in the upper 30 km of the crust (6.2-6.7 km/s in the upper and middle crust and 6.9-7.1 km/s below) which we interpret as structure inherited from the Labradorian orogen. Velocities in the adjacent Groswater Bay terrane are 6.0-6.55 km/s in the upper and middle crust and 6.6-6.95 km/s in the lower crust. The entire Grenville crust is underlain by a 15-20 km thick high-velocity lower crustal (HVLC) wedge consisting of an upper layer (7.1-7.4 km/s) and a lower layer (7.6-7.8 km/s). The HVLC wedge is interpreted as an underplated layer formed during Iapetan rifting. This interpretation is based on the correlation with the 615 Ma Long Range dykes onshore and the eastward termination of the wedge at the Cartwright Arch. Similar HVLC layers are found offshore western Newfoundland, suggesting that the underplating may be a continuous feature along the passive Grenvillian margin. The Cartwright Arch is characterized by velocities of 6.4 km/s and 4 km thick sediment sequences (4.3-5.7 km/s) in the surrounding basin, interpreted as an extensional basin with basaltic magmatism within the arch. The Grenville front is clearly marked by a decrease of velocities in the Makkovik Province (5.8-6.4 km/s in the upper and middle crust, 6.65-6.85 km/s in the lower crust) and a gradual thickening of the crust (not including the HVLC layer) from 30 km in the Grenville Province to 35 km in the Makkovik Province.