Heat flow data from a number of continental shield regions shows a trend of relatively low to high values from Archean cratons to Proterozoic mobile belts. Of the two end-member explanations for this trend, low heat production in Archean crust or a relatively thick cratonic lithosphere, the latter has come to be generally preferred. Such an explanation assumes a strong, one-to-one correspondence between the mantle component of surface heat flow and local lithospheric thickness. This assumption has been well validated below oceans and its applicability to continental lithosphere has gone largely unchallenged. It is, however, not fully valid. This is demonstrated through numerical models that allow continents to form over a convecting mantle. Model continents consist of a core region of thickened crust and mantle residuum and a peripheral region of thick crust; analogs to a craton and a mobile belt, respectively. Despite a thicker thermal lithosphere in the core relative to the periphery, the equilibrium surface heat flux across a continent shows little variation. The finite thermal conductivity of buoyant continental material is at the heart of this behavior as it allows continents to enforce a spatially near constant heat flux condition on the mantle below. Such a condition is associated with a weak correspondence between mantle heat flow and lithospheric thickness, defined thermally or mechanically. This general result, together with specific modeling results applied to heat flow data, suggests that variable lithospheric thickness is most likely not the primary cause of heat flow variations near Archean cratons, leaving differing degrees of crustal heat production as the more likely candidate.
AGU Index Terms: 8120 Dynamics of the lithosphere and mantle; 8130 Heat generation and transport; 8121 Dynamics, convection currents and mantle plumes; 8110 Continental tectonics-general
Keywords/Free Terms: Continental heat flow, cratons, mantle convection.
JGR-Solid Earth 96JB02849
Vol. 102
, No. B1
, p. 709