Periodic Reporting for period 2 - TimeMan (RHEOLOGY OF EARTH MATERIALS: CLOSING THE GAP BETWEEN TIMESCALES IN THE LABORATORY AND IN THE MANTLE) Reporting period: 2020-09-01 to 2022-02-28 Summary of the context and overall objectives of the project Most large-scale geological processes such as plate tectonics or mantle convection involve flow of rocks at infinitely slow velocities, not noticeable at human timescale. Laboratory experiments can now reach the high-pressure, high-temperature conditions of the interior of the Earth, but they are much faster. The laws determined from these experiments performed at human timescales must be extrapolated to Earth’s conditions over several orders of magnitude. This leads to highly questionable results as demonstrated by recent comparison with surface geophysical observables.Strain rates couple space and time. We cannot expand time, but we can now reduce length scales. By using the new generation of nanomechanical testing machines in transmission electron microscopes, we can have access to elementary deformation mechanisms and, more importantly, we can measure the key physical parameters which control their dynamics. At this scale, we can have access to very slow mechanisms which were previously out of reach. This approach can be complemented by numerical modelling. By using the recent developments in modelling the so-called “rare events”, we will be able to model mechanisms in the same timescales as nanomechanical testing. Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far After one year, we are forging the tools necessary to the project. We have now some experience in realizing nanomechanical tests at room temperature in a transmission electron microscope and by nanoindentation. On the numerical simulation side, we have developped a new approach to model atomic diffusion in MgO over 14 orders of magnitude of timescales from 10 ns to 10 days Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far) By combining, nanomechanical testing and advanced numerical modelling of elementary processes, we propose to elaborate a new generation of rheological laws, based on the physics of deformation, which will explicitly involve time (i.e. strain rate) and will require no extrapolation to be applied to natural processes.Applied to olivine, the main constituent of the upper mantle, this will provide the first robust, physics-based rheological laws for the lithospheric and asthenospheric mantle to be compared with surface observables and incorporated in geophysical convection models. In Nanomechanical testing, the specimens are smaller than a red blood cell
