What the mantle sees

Abstract

The effects of continents on mantle heat flow are explored through a synthesis of heat flow data analysis and theoretical modeling. The data employed are from the Canadian Shield and the Canadian Appalachians and consist of both surface heat flow measurements and measurements of crustal heat production. The combined data sets, together with gravity and seismic information, which is used t o help constrain crustal structure and composition, suggest that the mantle component of surface heat flow is low, between 10 and 15 mW/m2, and relatively uniform across a large portion of central t o eastern Canada. Surface heat flow variations across the region covered can be well accounted for by observed variations in crustal heat production, i.e., no mantle heat flow variations need to be invoked. Laboratory experiments and numerical simulations, that explore the coupling between continents and the convecting mantle from a modeling based point of view, show how large, buoyant continents can locally constrain heat flux variations in the mantle below. Relative to what occurs in model oceanic regions, the equilibrium thermal condition imposed on the mantle by model continents is one of low and nearly uniform heat flux. Such a condition is consistent with the inferences drawn from the Canadian heat flow data. Theoretical models also imply that the local thermal constraint imposed on t h e mantle by continents can cause mantle heat flow to be relatively weakly correlated with tectonic age variations, lithospheric thickness variations, and local mantle flow patterns below tectonothermally stable continental regions. Show more