Periodic Reporting for period 4 - TimeMan (RHEOLOGY OF EARTH MATERIALS: CLOSING THE GAP BETWEEN TIMESCALES IN THE LABORATORY AND IN THE MANTLE)
Periodo di rendicontazione: 2023-09-01 al 2025-02-28
Most large-scale geological processes—such as plate tectonics and mantle convection—involve the flow of rocks at velocities so slow that they are imperceptible on human timescales. While laboratory experiments can now replicate the high-pressure, high-temperature conditions of Earth’s deep interior, they must do so at much higher deformation rates. This discrepancy requires extrapolating physical laws over several orders of magnitude in time and strain rate—an approach that introduces significant uncertainty. Recent comparisons with geophysical observations have highlighted how these extrapolations can lead to unreliable or even misleading predictions.
The overarching objective of this ERC project was to overcome these limitations by exploring a fundamentally new approach to rock deformation. Rather than expanding experimental timescales—which is not physically feasible—we reduced spatial scales. By employing next-generation nanomechanical testing within transmission electron microscopes (TEM), we gained access to the fundamental mechanisms that control how minerals deform. At the nanometer scale, we could observe ultra-slow processes and directly measure the physical parameters governing them. These advances were tightly integrated with state-of-the-art computational modeling, allowing us to connect atomic-scale dynamics with the large-scale behavior of rocks.
As a result, this project delivered major breakthroughs in mineral physics and laid the foundation for a new generation of physically grounded models of Earth’s interior. Our conclusions emphasize that understanding geological deformation requires going beyond traditional experimental extrapolations and incorporating the real atomic-level physics of crystalline defects. The findings have broad implications for geoscience, materials science, and planetary modeling.
The overarching objective of this ERC project was to overcome these limitations by exploring a fundamentally new approach to rock deformation. Rather than expanding experimental timescales—which is not physically feasible—we reduced spatial scales. By employing next-generation nanomechanical testing within transmission electron microscopes (TEM), we gained access to the fundamental mechanisms that control how minerals deform. At the nanometer scale, we could observe ultra-slow processes and directly measure the physical parameters governing them. These advances were tightly integrated with state-of-the-art computational modeling, allowing us to connect atomic-scale dynamics with the large-scale behavior of rocks.
As a result, this project delivered major breakthroughs in mineral physics and laid the foundation for a new generation of physically grounded models of Earth’s interior. Our conclusions emphasize that understanding geological deformation requires going beyond traditional experimental extrapolations and incorporating the real atomic-level physics of crystalline defects. The findings have broad implications for geoscience, materials science, and planetary modeling.
From the outset, the project focused on the role of microscopic defects in controlling the mechanical behavior of rocks. Particular attention was given to grain boundaries—the interfaces between individual crystals—which play a crucial role in controlling large-scale flow. In particular, we resolved a long-standing discrepancy between theoretical and experimental descriptions of grain boundaries in magnesium oxide (MgO, a component of the lower mantle)). By incorporating realistic features such as non-stoichiometry and point defects, we reconciled simulations with laboratory observations.
Building on this, we extended our modeling work to olivine, a major mantle mineral. We were the first to describe tilt and twist boundaries in olivine and revealed the intricate structural complexity of real grain boundaries in silicate materials. These advances provide essential inputs for more accurate modeling of rock flow in the Earth’s mantle.
In parallel, we used high-resolution nanomechanical testing within TEM setups to access deformation mechanisms at unprecedented small scales. One of the project’s most significant achievements was the first direct observation and measurement of a grain boundary flowing after undergoing amorphization—a transition from a crystalline to a glassy state that enables boundary sliding. This mechanism had previously been proposed theoretically but never demonstrated with such clarity.
We also characterized how amorphous olivine deforms across a strain-rate range spanning more than 20 orders of magnitude. This invariance is unprecedented in materials science and strongly contrasts with the behavior of other key minerals, such as bridgmanite, which exhibits different deformation mechanisms under natural versus laboratory conditions. These findings demonstrate the importance of new deformation pathways and highlight the inadequacy of relying solely on traditional scaling laws.
Another key outcome was the identification of dislocation climb as a dominant deformation mechanism at geological strain rates—both in the deep mantle and, remarkably, in quartz in the lithosphere. This mechanism has long been overlooked due to its slow nature and the experimental challenges in accessing it, yet our findings place it at the center of rock deformation processes at natural conditions.
These scientific results have been disseminated through numerous peer-reviewed journal publications, presentations at major international conferences, and invited talks. They have stimulated cross-disciplinary interest, particularly among researchers in mineral physics, geodynamics, materials science, and solid-state physics.
Building on this, we extended our modeling work to olivine, a major mantle mineral. We were the first to describe tilt and twist boundaries in olivine and revealed the intricate structural complexity of real grain boundaries in silicate materials. These advances provide essential inputs for more accurate modeling of rock flow in the Earth’s mantle.
In parallel, we used high-resolution nanomechanical testing within TEM setups to access deformation mechanisms at unprecedented small scales. One of the project’s most significant achievements was the first direct observation and measurement of a grain boundary flowing after undergoing amorphization—a transition from a crystalline to a glassy state that enables boundary sliding. This mechanism had previously been proposed theoretically but never demonstrated with such clarity.
We also characterized how amorphous olivine deforms across a strain-rate range spanning more than 20 orders of magnitude. This invariance is unprecedented in materials science and strongly contrasts with the behavior of other key minerals, such as bridgmanite, which exhibits different deformation mechanisms under natural versus laboratory conditions. These findings demonstrate the importance of new deformation pathways and highlight the inadequacy of relying solely on traditional scaling laws.
Another key outcome was the identification of dislocation climb as a dominant deformation mechanism at geological strain rates—both in the deep mantle and, remarkably, in quartz in the lithosphere. This mechanism has long been overlooked due to its slow nature and the experimental challenges in accessing it, yet our findings place it at the center of rock deformation processes at natural conditions.
These scientific results have been disseminated through numerous peer-reviewed journal publications, presentations at major international conferences, and invited talks. They have stimulated cross-disciplinary interest, particularly among researchers in mineral physics, geodynamics, materials science, and solid-state physics.
This project has advanced beyond the state of the art by integrating multi-scale modeling with innovative nanomechanical experiments to study rock deformation under extreme conditions. Traditional approaches have relied heavily on extrapolating laboratory data obtained at high strain rates. By contrast, this project developed a framework grounded in physical mechanisms observed at the atomic scale, allowing more accurate modeling of mineral behavior at natural strain rates.
One of the key advances was demonstrating that deformation mechanisms such as grain boundary sliding and dislocation climb can be directly observed and quantified using nanoscale mechanical testing in transmission electron microscopes. This made it possible to explore deformation processes previously inaccessible to experimentation, especially at extremely low strain rates. These insights were integrated into numerical models that bridge atomic-scale defect motion and the rheological behavior of mineral aggregates.
Several findings emerged that were not anticipated at the outset, enabled by the flexibility of the project's experimental and modeling approaches. These include the identification of amorphization as a facilitator of grain boundary mobility, the observation of complex dislocation behaviors such as mixed climb, and the exploration of deformation in amorphous silicates under electron irradiation. Together, these discoveries offer new perspectives on how rocks deform in both the lithosphere and deep mantle.
Looking ahead, the methodologies developed in this project are being extended to other mantle phases and across phase transitions, contributing to more robust models of Earth’s interior. The combination of detailed experimental insights and predictive modeling offers a path forward for advancing the understanding of planetary dynamics on solid physical grounds.
One of the key advances was demonstrating that deformation mechanisms such as grain boundary sliding and dislocation climb can be directly observed and quantified using nanoscale mechanical testing in transmission electron microscopes. This made it possible to explore deformation processes previously inaccessible to experimentation, especially at extremely low strain rates. These insights were integrated into numerical models that bridge atomic-scale defect motion and the rheological behavior of mineral aggregates.
Several findings emerged that were not anticipated at the outset, enabled by the flexibility of the project's experimental and modeling approaches. These include the identification of amorphization as a facilitator of grain boundary mobility, the observation of complex dislocation behaviors such as mixed climb, and the exploration of deformation in amorphous silicates under electron irradiation. Together, these discoveries offer new perspectives on how rocks deform in both the lithosphere and deep mantle.
Looking ahead, the methodologies developed in this project are being extended to other mantle phases and across phase transitions, contributing to more robust models of Earth’s interior. The combination of detailed experimental insights and predictive modeling offers a path forward for advancing the understanding of planetary dynamics on solid physical grounds.