MC2 - Mantle Circulation Constrained

This project brings together researchers from 8 UK universities, with expertise in a wide range of disciplines including geodynamics, mineral physics, seismology, geochemistry, palaeomagnetism, magnetohydrodynamics, dynamic topography and petrology to constrain mantle circulation.

The MC² project (2020-2025) will use plate motion histories to drive numerical mantle convection models for simulating mantle circulation using the national supercomputer Archer2. By comparing model outputs to a diverse set of observations, we will constrain mantle circulation during the Phanerozoic, including the poorly understood hot mantle upwellings. Particular focus will be on the large upwellings that have produced massive magmatic outpourings resulting in Large Igneous Provinces.

Detail

The project will test numerical mantle circulation models by comparing their predictions of both present day mantle structure and predictions of the evolution of the mantle over the past 1 billion years with observations. Inversions will be made for improved thermodynamic databases of mantle mineral properties.

The present-day mantle structure will mostly be tested using seismological observations. We will use the properties of mantle minerals from our thermodynamic databases to predict the seismic structure resulting from the dynamic models. Since these models also track mantle flow, these dynamic models can also predict the anisotropy of the seismic structures wherever the flow induces lattice preferred orientation. The various seismic predictions will be compared to the findings of seismologists in the team who will invert seismic data to produce global and regional models of seismic structure. Other seismology team members will focus on specific characteristics of the dynamic models including anisotropic signatures and seismic multi-pathing. Together these seismic studies will help us tightly constrain the active structures in the mantle ranging from sharp to broad features.

Predictions of mantle evolution will be tested using dynamic topography, geochemistry and core dynamics. The mantle models will predict deformation of the surface, which team members will test against their estimates of observed dynamic topography over the Phanerozoic. The mantle circulation models will also track the input and resulting flow of unique uranium isotope tracers that entered the mantle when the oxygen levels jumped in the atmosphere. These predictions will be tested by measuring these isotopes in samples from mid-ocean ridge basalts.

The temperature and composition of the mantle upwellings generating magmas at ocean islands will be constrained by petrology methods that measure aluminium in spinels in olivines from these locations. Finally, the deep structure of the models back in time will be tested using observations of the magnetic field. As the mantle models also provide the heat flow out of the core, geodynamo models will be used to predict the variations in the magnetic field over the Phanerozoic. These predictions in magnetic field variations will be tested by paleomagnetic measurements.

Together, the combination of all these methods and observations will constrain mantle circulation in space and time, leading to a step forward in our understanding as to how the mantle leads to significant changes to Earth's surface over geologic time.