Generation of mega‐plumes from the core‐mantle boundary in a compressible mantle with temperature‐dependent viscosity

Abstract

We have investigated the development of axisymmetric mantle plumes in a compressible mantle with temperature‐dependent viscosity, using two different values for the thermal activation energy. Thermodynamic parameters were based on realistic Earth values in the shallow mantle. We assumed a compressible mantle with a phase transition and a two layer viscosity structure (mantle 30 times more viscous beneath the phase change). A dramatic transition in plume dynamics occurred as the thermal activation energy was increased from 250 to 500 kJ mol −1 . A “mega‐plume” was formed from the merging of small‐scale instabilities swept into the plume's axis, rapidly flushing the entire contents of the hot thermal boundary layer into the upper mantle. Hot plume material with a temperature anomaly of 250 K reached the lithosphere for our assumed temperature drop of 500 K across the base of the mantle. Viscous heating over four orders of magnitude greater than chondritic radiogenic sources was observed during the initial plume‐lithosphere interaction.