Using as a case study a granulite from the Kerala Khondalite Belt, India, we show that a former anatectic melt can be preserved as tiny (<25 μm) droplets within refractory minerals,in this case garnet. The melt is either fully crystallized as a Qtz-Ab-Kfs-Bt cryptocrystalline aggregate (“nanogranite”), or completely glassy in inclusions <15 μm. Both nanogranite and glassy inclusions have a peraluminous, ultrapotassic granitic composition that, in this case, does not correspond to a “minimum melt” and points to high melting temperatures, in agreement with the ultrahigh-temperature origin of the rock. This discovery indicates that peritectic minerals, growing during incongruent melting reactions, act as hosts for inclusions of anatectic melt, and that in the general case of slow cooling of the crust these inclusions will occur as nanogranite. Exceptionally, in the smallest inclusions, glass may be present due to inhibition of crystallization. Our results extend the frontiers of petrological and geochemical research in crustal melting, as the composition of natural anatectic melts can be directly analyzed rather than assumed

The dacite of El Joyazo contains abundant metapelitic xenoliths. These can be divided into two main types: garnet-biotite-sillimanite and spinel-cordierite xenoliths. In the xenoliths the widespread occurrence of rhyolitic glass as interstitial films, foliation-parallel layers and primary melt inclusions in all mineral phases indicates that these assemblages developed in the presence of a melt phase, i.e. during anatexis. The composition of the interstitial glass is comparable to that of the melt inclusions, suggesting that melt was locally produced. Phase equilibria indicate that anatexis occurred at P-T conditions of 5–7 kbar and 850±50°C.Several microstructural lines of evidence show that melt extraction was assisted by deformation during foliation development, and that on the scale of the xenoliths (up to 50 cm) melt escaped mainly by flow along foliation planes. The development of a syn-anatectic foliation also suggests that metapelitic rocks were involved in high-grade metamorphism and partial melting prior to fragmentation and dispersion in the host dacite.Mass balance calculations, based on the chemical composition of interstitial glass and melt inclusions in minerals, the bulk xenoliths and representative samples of potential pelitic sources support a model wherein the xenoliths represent restites after the extraction of 30 to 55 wt.% melt from graphitic metapelite protoliths similar to the rocks constituting the surrounding Alpujarride metamorphic complex.