Survival of hadean remnants in a dynamic mantle
Plate tectonics drives the formation and destruction of crust and introduces surface material into the deep Earth, while mantle convection mixes materials back together, erasing their diversity. Geochemical heterogeneities in modern volcanics indicate the survival of Hadean (≈ 4.5 Ga) remnants, and their mare existence raises first-order questions: What is the nature of the material carrying the odd geochemical signatures? How can Hadean material survive in an actively convecting mantle? What are the physical properties of material that can be preserved for billions of years, and yet that can be entrained in mantle plumes? Can Hadean remnants be stored in the structures seismically imaged in the lowermost mantle? Answering these questions is the challenging aim of SHRED. I will define the location, dimensions, structure, physical nature and composition of the ‘storage site’ of old material and I will constrain the conditions necessary for the material to be sampled in hotspots.
To reach the goal, I will assemble a unique group of scientists that will combine the most innovative geochemical tools with the latest physical modeling of inner Earth. I will characterize the isotopic diversity of modern intraplate volcanism and develop new geochemical tools to determine the age and size of heterogeneities in mantle plumes. These observations represent key constraints for geophysical models that will unravel, in a fluid-dynamically consistent framework, the evolution of mantle heterogeneities. Innovative simulations with particle tracing will determine the geographical origin of upwelling material and evaluate its relationship to deep seismic structures. Simulations focussed on mantle mixing will explore the physical conditions required for the survival of heterogeneities on billion-year-time-scales. This unique combination of expertise will provide answers to decades-old questions raised independently in mantle geochemistry and mantle geophysics.