Energetics and heat budget of the earth's mantle convection constrained by plume and slab dynamics

Understanding the heat budget and energetics of the Earth's mantle convection is important for constraining the thermal evolution history and chemical composition of the Earth's core and mantle. Mantle plumes and subducted slabs are two most important agents for energy transfer in the Earth's mantle convection. With numerical modeling and theoretical analysis, here we show that surface observations of plumes and slabs can be used to constrain the internal heating ratio of the mantle, the core-mantle boundary (CMB) heat flux and the viscous dissipation in the plate bending zones. We also show that including more realistic physics may significantly affect the surface manifestation of the conventional mantle plume model. Our main conclusions are summarized as below. First, mantle plumes account for 80%-90% of the CMB heat flux. Due to the steeper adiabatic gradient of plumes compared with ambient mantle, plume heat flux and plume excess temperature decrease approximately by a factor of two during plumes' ascent. In order to reproduce surface plume-related observations, ∼70% internal heating ratio of the Earth's mantle, i.e. ∼11 TW of CMB heat flux, is required. Second, the total viscous dissipation and the total adiabatic heating balance out each other at any instant in time for compressible mantle convection. The viscous dissipation in the plate bending zones only account for <10% of the total viscous dissipation in the Earth's mantle, thus plays a minor role in Earth's thermal evolution history. Third, instead of causing surface uplift as suggested by convectional plume models, a plume head temporarily ponding below the 660-km phase boundary may cause significant surface subsidence over an extended time period before it reaches surface and generates flood basalt eruptions. Therefore, the observed surface subsidence history in many flood basalt provinces may be used as diagnostics for identifying plume-induced flood basalt events.