PALEO HEAT-FLOW OF EASTERN CANADA PASSIVE MARGINS

Tectonic subsidence rates, derived from several wells in the Labrador Sea and offshore Nova Scotia and Newfoundland, were used to estimate the paleo heat flow along the margins of eastern Canada. If tectonic subsidence is caused by the cooling of the lithosphere only, the transient component of the heat flow (i.e., the heat flow in excess of background heat flow) can be estimated directly from subsidence data. For the Nova Scotia and the Labrador Sea margins, the analysis shows that the transient component of the heat flow decreased markedly from 28-56 mW . m-2, immediately after rifting, to a present value between 7 and 14 MW . M-2 depending on boundary conditions. The analysis shows a distinctive difference between the evolution of the Labrador Sea and that of the northeastern Newfoundland margin where it is estimated that the transient component of the heat flow exceeded 100 MW . m-2 after rifting and dropped rapidly to very low values. The study suggests that the subsidence of the Newfoundland margin was not caused by cooling only but required an additional mechanism such as lower-crustal phase transformations or continuing extension after continental breakup with ductile deformation in the lower crust and upper mantle. The estimated transient heat flow was used to calculate the average present surface heat flow in eastern Canada's margins, which is the sum of heat flow from the mantle, crustal heat production, and the transient cooling of the lithosphere. The calculated heat flow compares well with heat flow density data obtained from bottom hole temperature measurements.