Scaling up: Nanoscale insights into tectonic phenomena

Tectonic-scale geological phenomena are fundamentally controlled by nanoscale physiochemical mineral processes. Understanding these processes across multiple length scales is crucial for determining how mass and stress are transferred during tectonism. Minerals exhibit complex structure-property relationships that govern their mechanical and chemical behaviour, yet these relationships have been historically underexplored in Earth sciences. Advances in nanotechnology and instrumentation, including techniques such as high-resolution electron backscatter diffraction, electron channeling contrast imaging, transmission electron microscopy, and atom probe tomography, now enable unprecedented investigations of nanoscale features in geomaterials. The correlative approach has given rise to the emerging field of nanogeology, which helps bridge the gap between nanoscale and tectonic-scale processes. Recent nanoscale investigations have demonstrated the fundamental role of structural defects and element mobility in controlling the mechanical properties and deformation behaviour of minerals in the brittle-ductile regime. For example, detailed microanalyses of garnet reveal a novel precipitation hardening mechanism where Fe diffused along grain boundaries of recrystallized garnet, nucleating Fe-rich nanoclusters. These clusters act as barriers to dislocation migration, resulting in localized strain hardening. This process provides a potential mechanism for mechanical strengthening in the lower continental crustsubsequently influencing large scale geodynamic processes. Similar investigations of pyrite, a critical metal-bearing sulfide mineral, reveal nanoscale fluid inclusions that facilitate the diffusion of trace elements into crystalline defects, such as dislocations, inhibiting their movement, and leading to mineral hardening. Such findings are particularly significant, as the brittle-to-ductile behaviour of sulfides has been directly linked to the upgrading of critical metal deposits. These discoveries highlight the dynamic interplay between nanoscale element mobility and the rheology of minerals, and by consequence, larger mass transfer dynamics. Moreover, deformation-driven element redistribution raises questions about the reliability of deformed minerals as petrological tools. For instance, the deformation of zircon may compromise its use as a robust geochronometer, whereas the deformation of garnet may influence its reliability as a thermobarometer. A deeper understanding of element mobility in the presence of defects is essential for accurately interpreting geochemical data and reconstructing tectonic histories. Overall, these breakthroughs highlight the pivotal role of nanoscale processes in shaping tectonic phenomena, emphasizing the need for a multi-scale approach to understanding Earth's dynamic behaviour.