Thermal history and subsidence of rifted continental margins—evidence from wells on the Nova Scotian and Labrador Shelves

• Published in: Canadian Journal of Earth Sciences
• Main Author: Keen, C. E.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 1979
• Subjects: General Earth and Planetary Sciences; Newfoundland; Labrador Shelf; Orphan Knoll
• Online Access: http://dx.doi.org/10.1139/e79-046; http://www.nrcresearchpress.com/doi/pdf/10.1139/e79-046

The subsidence histories of the Labrador and Nova Scotian rifted continental margins have been determined from biostratigraphic data for 11 deep exploratory wells off Nova Scotia, for five wells off Labrador, for three wells northeast of Newfoundland, and for one well off the northeast coast of the United States of America. The components of subsidence, due to sediment loading, and when possible due to loading by changes in eustatic sea level, were removed, leaving that part of the subsidence, the tectonic subsidence, caused by cooling of the lithosphere or by other deep seated processes. The thermal cooling model theoretically predicts a linear relationship between tectonic subsidence and t½, where t is the time since subsidence began. This relationship should be obeyed during the first tens of Ma of subsidence. The slope of this curve depends upon the temperature to which the crust and upper mantle were heated during the initial rifting stage and can be used to derive the temperature–time history within the sediments, the present temperature distribution, and geothermal gradient. The data show that the observed subsidence curves behave in accordance with the thermal cooling model, at least during the first 80 Ma after subsidence began and obey the equation y = 300(± 80)t 1/2 m, where y is the tectonic subsidence. The slopes of the subsidence curves are similar for the Labrador Shelf, the Nova Scotian Shelf, and the shelf off the northeastern U.S.A. More rapid and variable subsidence occurs northeast of Newfoundland and this may be associated, in a way yet to be established, with the anomalous foundered continental crust near the Orphan Knoll and Flemish Cap micro-continents which lie close to this area. After about 80 Ma, the subsidence appears to depart from the linear t 1/2 law in a manner similar to the subsidence curves for oceanic crust, but this is not well established by the data. The present temperatures and temperature gradients computed using the slope of the subsidence curves show good agreement ...