Conjectures on the thermal and tectonic evolution of the Earth

Abstract

The tectonic modes operating at any given time in the Earth are intimately related to the thermal evolution, since tectonics is driven by heat removal from the Earth's interior. Conversely, the viability of a proposed tectonic mode depends on its ability to remove heat from the interior as well as on its inferred consistency with geological evidence. On this basis it seems that plate tectonics may have been dominant only in the later part of Earth history, and that proposed earlier modes involving only a subcrustal thermal boundary layer may never have been dominant unless the effects of the basalt-eclogite transition or of latent heat removal were able to enhance their heat transport efficiency. More generally, the tectonic mode driven by the cool thermal boundary layer at the top of the mantle may have depended very sensitively on the effects of composition and latent heat on density. Calculations indicate that plumes could have operated through most of Earth history at about the present level of activity, unless heat conduction from the core into the mantle has been inhibited in later times, in which case they would have been hotter and more active in earlier times. Plumes could not have substituted for plate tectonics because plumes and plates are driven by different thermal boundary layers that operate largely independently.