One of the major challenges in the study of geological processes occurring in the Earth’s crust and mantle derives from the impossibility of direct access to these portions. However, recent methodological and technological advances have improved our capability to observe and quantify the fingerprints of geological processes at much finer spatial and temporal resolutions. Microstructures within igneous, metamorphic, and deformed rocks are archives preserving abundant information about processes occurring throughout the crust and the mantle, such as mantle melting and metasomatism, heating and cooling events, fluid mobility, the timing and location of nucleation and crystal growth, mechanisms and timing of deformation, fluid dynamical behaviour during magma crystallization.

The study of microstructure provides direct information on the history and timescales of geological processes, allowing the development of chemically- and physically-based models of deep and surface processes acting under equilibrium and disequilibrium conditions. They provide fundamental piece of information for short- and long-term eruption forecasting, planetary evolution, crustal differentiation, deformation, and exhumation, and global volatile cycling.

The Big Fat Session of the Year focuses on the study of microstructures sensu lato covering the entire range of igneous and metamorphic petrology in various tectonic settings. Contributions in this session will include new applications of well-established techniques, showcase development of new microstructural and analytical techniques, careful sample characterization from micro- to macroscopic scale prior to textural, chemical and isotopic analyses. We present multidisciplinary studies focused on linking quantitative datasets to field and geophysical observations challenging the difficulties related to processes marked by strong disequilibrium.