Heat-blanketed convection and its implications for the continental lithosphere

TL;DR

This study investigates how a heat-enriched continental crust influences mantle convection, revealing that the distribution and thickness of heat-producing elements significantly affect heat transfer and mantle dynamics.

Contribution

It introduces a simplified convective model to systematically analyze the impact of a heat-blanketed layer on mantle convection, a novel approach in this context.

Findings

Thinner heated layers enhance surface heat flux and convective vigor.

Effects depend on the ratio of heated layer thickness to boundary layer thickness.

Continental presence likely does not significantly alter Earth's overall cooling rate.

Abstract

Earth's continents are characterized by a strong enrichment in long-lived radioactive isotopes. Recent estimates suggest that they contribute to 33\% of the heat released at the surface of the Earth, while occupying less than 1\% of the mantle. This distinctive feature has profound implications for the underlying mantle by impacting its thermal structure and heat transfer. However, the effects of a continental crust enriched in heat-producing elements on the underlying mantle have not yet been systematically investigated. Here, we conduct a preliminary investigation by considering a simplified convective system consisting in a mixed heated fluid where all the internal heating is concentrated in a top layer of thickness $d_{HL}$ (referred to as "heat-blanketed convection"). We perform 24 numerical simulations in 3D Cartesian geometry for four specific set-ups and various values of $d_{HL}$. Our results suggest that the effects of the heated layer strongly depend on its thickness relative to the thickness of the thermal boundary layer ($\delta_{TBL}$) in the homogeneous heating case ($d_{HL} = 1.0$). More specifically, for $d_{HL} > \delta_{TBL}$, the effects induced by the heated layer are quite modest, while, for $d_{HL} < \delta_{TBL}$, the properties of the convective system are strongly altered as $d_{HL}$ decreases. In particular, the surface heat flux and convective vigour are significantly enhanced for very thin heated layers compared to the case $d_{HL} = 1.0$. The vertical distribution of heat producing elements may therefore play a key role on mantle dynamics. For Earth, the presence of continents should however not affect significantly the surface heat flux, and thus the Earth's cooling rate.