Stagnant lid convection and the thermal subsidence of sedimentary basins with reference to Michigan

Abstract

[1] The thermal subsidence of basins formed above thick continental lithosphere differs from that of young passive margin basins and of young oceanic crust in that stagnant lid convection supplies significant heat flow from the asthenosphere. The lithosphere eventually approaches thermal equilibrium where the convective heat added to its base balances the heat lost by conduction to the surface. This paper presents a simple parameterization that quantifies these effects for modeling basin subsidence. The convective heat flow scales with the current lithosphere thickness squared while the conductive heat flow scales inversely to current lithospheric thickness. The predicted thermal subsidence rate scales to the difference between the conductive and convective heat flows and wanes gradually over hundreds of millions of years. The formalism can be modified to represent thermal subsidence where plume material has ponded within a catchment of locally thinned lithosphere. The base of the plume material forms a stable stratification that suppresses convective heat flow from below while heat continues to conduct to the surface by conduction. The predicted initial thermal subsidence rate scales with the large difference between conductive and zero convective heat flow. It is thus much greater than beneath lithosphere underlain by ordinary asthenosphere for a given amount of total eventual thermal subsidence. The paper compares thermal subsidence predictions from the models with and without plumes with sedimentation data from the Michigan basin. Observed initial Late Cambrian through Lower Devonian sedimentation in the Michigan basin is rapid as expected from the plume model, but the Ordovician sedimentation rate is slower than before and after. It is conceivable that this irregularity in the sedimentation curve is associated with low eustatic sea level and sediment-starved conditions at the basin center in the Ordovician and Early Silurian periods, as opposed to irregular tectonics. Sedimentation poorly resolves a long tail of gradual subsidence that may extend to the present.

Speculations on the formation of cratons and cratonic basins

“…1) or twice that of the oceanic lithosphere, their thermal time constant should be about four times that of extension basins. This difference can account for the long time scale over which subsidence occurs in cratonic basins, and has for this reason been appealed to by a number of authors for many years (see Sleep et al 1980, Sleep 2009, Allen and Armitage 2012. But it is difficult to understand how the necessary thermal perturbation is produced.…”

Small-scale convection beneath oceans and continents

“…Equating the conductive heat flow through the rigid lithosphere with convective heat flow into the bottom of the lithosphere from (17) and (21) gives…”

“…These equations hold when the predicted heat flow is significantly less than the steady state value. Sleep [17,52] discussed the final approach to steady state. Equation (32) has a simple calibrated form for linear rheology n=1:…”

“…Small-scale convection and mantle plumes are obvious candidates. The net heat flow added by plumes is small because ponded plume material has a stably stratified base that suppresses subsequent stagnant-lid convection [17,20]. Drag from the lateral movement of plates [60].…”

“…It is modestly thinner than cratonal lithosphere. Modern continental basin models involve ~200 km thick platform lithosphere [17,18].…”