Mantle Circulation Constrained (MC2): A multidisciplinary 4D Earth framework for understanding mantle upwellings

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The theory of plate tectonics revolutionised the Earth sciences and had impacts across society, by providing a framework to understand the motion of Earth's surface. However, plate tectonic theory does not tell us about the processes deeper in the Earth that drive plate motions, nor does it explain some of the most dramatic events in Earth history: the breakup of plates and outpouring of huge volumes of lava. The next required breakthrough is to make this leap, from a 2D description of plates to understanding the truly 4D nature of Earth's interior processes.Motion of the Earth's interior, its circulation, involves both upwelling and downwelling. The upwelling flow in the Earth remains enigmatic, occurring in the present-day as both hot focused plumes, which are only just observable through modern seismic imaging techniques, and a hypothesised diffuse flow, which has evaded detection entirely. A third mode of mantle upwelling is currently dormant, making its mantle flow signature unknown. However, this dormant mode of flow drives massive outpourings of lava, and has been associated with continental breakup and mass extinction events.Our project's overall goal is to constrain how mantle upwellings operate within the Earth. We will investigate how plate tectonics is linked to mantle circulation, by combining the history of plate movements across Earth's surface with observations drawn from across the geosciences, and use these to constrain state-of-the-art 4D computational models of mantle flow.These advances are made possible by recent progress in disciplines from across the Earth sciences, expertise we bring together here in geodynamics, seismology, geomagnetism, geochemistry, petrology, and thermodynamics. We will constrain present mantle flow by gathering new seismic imaging data of the Earth's deep interior. We will constrain past mantle flow using newly collected data on the mantle's composition, past magnetic field, and the history of Earth's surface uplift. We will use these multidisciplinary approaches to generate the most spatially and temporally complete set of observational constraints on mantle circulation yet assembled.These observations will be used to constrain and improve models that calculate mantle circulation in an Earth-like 3D geometry, driven by plate motion histories (mantle circulation models, MCMs). This is a timely development capitalising on the only recently available record of plate motion over 1 billion years of Earth History. The MCMs predict the mantle's temperature, density, and velocity through time, providing a 4D model of the Earth. Uncertain inputs in these models such as mantle viscosity and composition will be investigated within the bounds provided by the project's geochemical and thermodynamic work packages that will develop new models of Earth's high pressure mineralogy and physical properties. We will test the present-day predictions of the MCMs by converting model outputs to predict density and material properties within the Earth, using our developments on mineral physics modelling. With these inputs and constraints, we will create the first accurate computational models of mantle circulation over the last 1 billion years, which will provide dynamical insight into what drives the diversity of upwellings in the Earth.This tightly integrated multidisciplinary project is absolutely essential to achieve the best constrained MCMs and advance our understanding of Earth's interior processes. The result will be a coherent mantle circulation record of one quarter of Earth's history, and a major advance in our understanding of how mantle upwellings have impacted planetary evolution over this period.