Mineral inclusions are not immutable: Evidence of post-entrapment thermally-induced shape change of quartz in garnet

Sheltered inside crystals, mineral inclusions preserve crucial information on the geological history of our planet. These allow estimation pressure and temperature trajectories metamorphic rocks, but also can tell about rock mineralogy, provenance, geodynamic petrogenetic processes. This is recovered under axiom that have remained immutable objects do not change shape after their entrapment. Conversely, we show post-entrapment modifications occur in high-T rocks from granulite-facies conditions. Here analyze orientation quartz within garnet, a common mineral. Our data reveal progressive irregularly-shaped forms formed at T<550 °C, to combined dodecahedron icositetrahedron geometries imposed by host garnet granulites equilibrated T>750 °C. Lack fluid quartz-garnet phase boundary indicates inclusion occurs thermally-induced grain diffusion, driven minimization surface energy host-inclusion system. Since acquire negative crystal entrapment, discovery redefines conceptual framework for application elastic thermobarometry, motivates reevaluation criteria syngenesis rocks.