Heat‐Blanketed Convection and its Implications for the Continental Lithosphere

Abstract

AbstractEarth's continental crust is characterized by a strong enrichment in long‐lived radioactive isotopes. Recent estimates suggest that the continental crust contributes 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 dHL (referred to as “heat‐blanketed convection”). We perform 24 numerical simulations in three dimensional Cartesian geometry for four specific set‐ups and various values of dHL. Our results suggest that the effects of the heated layer strongly depend on its thickness relative to the thickness of the thermal boundary layer (δTBL) in the homogeneous heating case (dHL = 1.0). More specifically, for dHL > δTBL, the effects induced by the heated layer are quite modest, while, for dHL < δTBL, the properties of the convective system are strongly altered as dHL decreases. In particular, the surface heat flux and convective vigor are significantly enhanced for very thin heated layers compared to the case dHL = 1.0. The vertical distribution of heat producing elements may therefore play a key role in mantle dynamics. For Earth, the presence of continents should however not affect significantly the surface heat flux, and thus the Earth's cooling rate.