Apparent episodic crustal growth arising from a smoothly evolving mantle

Crustal-growth curves are the same as crustal-age distributions only in the absence of crustal recycling into the mantle, and are likely to be very different for Earth. Phanerozoic crust is more elevated, on average, compared to the ancient cratons, and thus may be preferentially eroded and deposited onto the mobile ocean floor. Ultimately, this may lead to the preferential recycling of young crust into the mantle. A simplified crustal-growth model shows that preferential recycling of young crust can lead to an apparent peak in crustal growth at 2 3 Ga. Furthermore, the time dependence and uneven positioning of ocean-continent convergence (sites of contemporaneous crustal growth and removal) with respect to the continents are likely to lead to rather irregular age distributions for each individual continent, with an apparent episodicity on a scale of hundreds of millions of years. Finally, considerations of the physics of convection reveals that rapid changes in mantle temperature are strongly inhibited because of the temperature dependence of silicate rheology. Episodic global magmatism and hence episodic crustal growth are not expected from our understanding of mantle convection.