Elastic strength of the Slave craton at 1.9 Gyr and implications for the thermal evolution of the continents

Abstract

THE secular cooling of the Earth since its formation, together with the law of radioactive decay, imply that the Earth's internal heat generation and heat loss must have been two to three times higher in Archaean and Proterozoic times than today, but this inference is difficult to test directly. Here we present a flexural analysis of the Proterozoic Kilohigok basin, in the Archaean Slave craton of Canada, which shows that 1.9 Gyr ago the craton had an effective elastic thickness of only 12 ±4 km. Because the present effective elastic thickness of the region is ∼ 100 ±25 km, these results imply a two- to fourfold decrease in the thermal gradient beneath the Slave craton since 1.9 Gyr, and indicate that at 1.9 Gyr—700 Myr after the accretion of the continental lithosphere forming the craton—the thick continental root beneath this part of the Canadian shield had not yet formed.