Thinned and subsided continental crust on the rifted margin of Eastern Canada: crustal structure, thermal evolution and subsidence history

• Published in: Geophysical Journal International
• Main Authors: Keen, C. E., Barrett, D. L.
• Format: Text
• Language: English
• Published: Oxford University Press 1981
• Subjects: Articles; Canada; Orphan Knoll; Newfoundland
• Online Access: http://gji.oxfordjournals.org/cgi/content/short/65/2/443; https://doi.org/10.1111/j.1365-246X.1981.tb02721.x

Seismic refraction measurements were carried out using ocean bottom seismometers over foundered continental crust in Orphan Basin and Flemish Pass, on the continental margin north-east of Newfoundland. Tau- p travel time inversion, synthetic seismogram analysis and conventional layered model calculations were applied to the data. The results show that these outer regions of the margin are underlain by thinned continental crust, with a total depth to the M discontinuity of about 22 km. There are two main crustal layers with P -velocities of about 6.1 and 7.0 km s‐1 which appear to be homogenous, and separated by sharp interfaces. These are overlain by a layer in which P -velocities are about 5.5 km s‐1; this is interpreted to be Precambrian or Palaeozoic basement. Mesozoic and Cenozoic sediments cover the basement rocks, and are over 4 km thick. The results imply that crustal thinning to about 50 per cent of the original crustal thickness occurred. The gravity anomaly data show that the thin crust has a maximum horizontal extent of about 450 km, from the ocean—continent boundary near Orphan Knoll landward to the outer continental shelf. The subsidence history and thermal evolution of the region was computed, assuming that the observed thinning is produced by horizontal extension of the lithosphere. It is suggested that extension can only satisfy the observed crustal structure and elevation of the margin during the rift phase if more extension took place in the lower lithosphere than in the upper lithosphere. The computed subsidence is compared to the observed subsidence and the total amounts of subsidence are similar. However, the shape of the observed subsidence curves measured in deep exploratory wells differs significantly from the predicted subsidence, assuming cooling began when final continental breakup occurred in the Late Cretaceous. The temperature distribution within the lithosphere due to extension may be related to the flexural rigidity of the plate as a function of both time and position across the ...