Seismic Signature of Plumes and the Heat Budget of Earth's Mantle

Abstract

The long-lived paradox between geochemical arguments for two compositionally distinct mantle reservoirs and geophysical evidence for extensive mass exchange between upper and lower mantle has still not been resolved in a manner to reach consensus. Recently, finite frequency tomography has produced images of large lower mantle plumes, which potentially carry a significant amount of heat through the mantle. This raises the prospect that the dynamic role of these plumes is larger than inferred classically from observation of dynamic topography. A consistent evaluation of this question requires a combination of large-scale numerical forward simulations of mantle circulation, mineral physics and computational seismology, complementing the tomographic inversions. The most important aspect will be to test whether the seismic velocity images should be interpreted as a thermal boundary layer at the upper mantle, lower mantle boundary or if the anomalies reflect a multi-phase transition pattern. Thereby we estimate the heat transported by plumes through the mantle and the probability of mass exchange across this boundary. Tools to answer this question are: 1) high-performance computations of global mantle circulation based on 3D finite elements 2) Large-scale 3-D spectral element simulations of global wave propagation. A key aspect to the success of our study is the different computational requirements of the two codes: While the first is highly CPU demanding, the later is so with respect to memory. The possibility offered by DEISA to run simulations on different architectures would serve our project extremely well, as the two tasks can beneficially be distributed to the appropriate computing sites according to their requirements.