The mantle represents 84% of Earth’s volume. It plays a critical role in the dynamics of the Earth and many essential processes that shape our planet, including convection, crustal formation and recycling, and the planet’s heat and volatile budgets. Seismic wave velocity variations provide evidence for the presence of various mantle reservoirs with differences in temperature and/or composition. The lower mantle, or part of it, is a reservoir that contains compositionally distinct material, including recycled and potentially ancient primitive components not available anywhere else. Mantle plumes originate at different depths, from shallow upwellings in the upper mantle to deeply sourced plumes that rise from near the core-mantle boundary (CMB) at ~2800 km. As such, they are invaluable tools to help answer many unresolved questions about mantle composition and its coupling to geodynamics, both today and throughout geologic time.
In this lecture, we will focus on the applications of geochemistry and isotopic analyses, which are essential tools for documenting mantle heterogeneity, and examine three major, well-studied plume systems with high magmatic fluxes in three different tectonic settings: Hawai’i, Galápagos, and Kerguelen. Hawai’i has been quoted as the archetype of mantle plumes. We will show that it is in fact quite unique in many of its characteristics (e.g., plume flux, evolution through time, and chemical components).
New perspectives on the geochemical composition of the mantle have recently been developed from advancements in analytical techniques and novel isotopic systems, allowing the resolution of smaller isotopic variations in ocean island basalt samples. These new techniques and isotopic systems shed light on the presence, source, and age of heterogeneities in the deep mantle. Coupled to geodynamic studies, modern isotopic data continues to reveal the complex nature of mantle chemical reservoirs through time and the complicated interplay between these reservoirs and the physical processes that govern internal Earth dynamics.