Low plume excess temperature and high core heat flux inferred from non-adiabatic geotherms in internally heated mantle circulation models

Abstract

Heat transfer across the core mantle boundary (CMB) is fundamentally important to Earth’s internal energy budget. But the amount of heat entering the mantle from the core is poorly known. Classic arguments based on the dynamic topography over mantle hotspots suggest a rather modest core contribution to the mantle energy budget, on the order of 5–10%. Recent geodynamic studies, however, favor significantly higher values to overcome problems of insufficient internal mantle heat generation, and to satisfy constraints on the power requirements of the geodynamo and the thermal history of the core. Here, we use a high resolution mantle dynamics model to show that the non-adiabatic mantle geotherm which arises from internal mantle heating has an important effect in lowering the excess temperature of hot upwelling plumes by systematically decreasing the temperature differential between plumes and ambient mantle from the CMB toward the surface. This non-adiabatic effect of internally heated mantle flow may explain the unusually low plume excess temperatures inferred from the petrology of hotspot lavas, and implies current estimates of core heat flux based on hotspot topography should be raised perhaps by a factor of three.