The mantle is full of weird and wonderful phenomena. As tectonic plates sink into the mantle at subduction zones and hot material upwells to erupt at mid-ocean ridges and hot-spot volcanoes, the mantle is churned into a marble cake of thermal and chemical heterogeneity. At the core-mantle boundary, where the solid rocky mantle meets the liquid metal outer core, the differences in physical properties are so extreme (even more so than between the crust and the atmosphere!) that a menagerie of complex and variable structures have collected there over billions of years of dynamic processes.

 

By resolving these structures in seismic models and reconciling our observations with geodynamic simulations and compositional constraints from mineral physics experiments, we ultimately build a more holistic understanding of Earth's compositional and dynamic evolution. Current seismic models of the deep mantle most notable reveal two giant piles of thermochemically distinct material that sit on opposite sides of the core, reaching over 1,000 km up into the overlying mantle and extending laterally up to ~10,000 km. Seismologists model these structures as regions where seismic waves travel at slightly lower speeds than expected, and so they are referred to most commonly as Large Low-Velocity Provinces (LLVPs). Models also show much smaller features of even more extreme wave-speed reductions, called Ultra Low-Velocity Zones (ULVZs), which may collect at the edges of LLVPs and constitute the roots of very hot plumes, some of which traverse the entire mantle and erupt at the surface (e.g., Hawai'i, Iceland, Samoa, Kerguelen).​​ I have the great good fortune to study these structures, which together constitute the seismic landscape of Earth's deep mantle, as part of Ed Garnero's research group.

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