Nanorocks: a 10-year-old story

The presence of nanogranitoids (crystallized melt inclusions showing a granitic s.l. composition) in regionally metamorphosed migmatitic and granulitic terranes was documented for the first time in 2009. This important finding represented a hallmark event for crustal petrologists, demonstrating that the pristine composition of anatectic melts may be preserved and recovered in small objects hosted in peritectic minerals of high-grade metamorphic rocks. Many further occurrences were documented in rocks worldwide, from diverse geodynamic settings, from the Archean to Miocene, and these inclusions turned out to have diverse composition (from silicatic to carbonatitic). Therefore, we propose “nanorocks” as a comprehensive name for these crystallized melt inclusions. In the last decade, many studies demonstrated their utility in characterizing mechanisms of melting and in tracking crustal magma evolution. Although scholars are now able to easily recognize nanorocks in high-grade metamorphic rocks, only a few research groups remelt them by means of experimental devices because of a time-consuming preparation. However, when cutting-edge techniques are applied in addition to more routine ones, nanorocks do open new perspectives in crustal petrology.