Microgranitoid enclaves in granites - Globules of hybrid magma quenched in a plutonic environment

Microgranitoid enclaves (autoliths, cognate xenoliths, mafic inclusions) are common in high-level granitoid plutons. They have relatively fine-grained igneous (microgranitoid) microstructures¹, and many show evidence of having flowed in a magmatic condition². These features counter interpretations that the enclaves represent transformed solid fragments of diverse wall rocks^3-5 or restite^6-11. An alternative interpretation is that the enclaves represent globules of mafic magma that have mingled ('commingled') and quenched in the granitoid host magma^12-16. A detailed review of the literature, occurrence, morphology and composition of micro-granitoid enclaves strongly supports this view, hut indicates that the enclave magmas range in composition from mafic to felsic, and that magma-mixing may be involved in their formation¹⁷. I summarize here the main features of microgranitoid enclaves and briefly outline the possible processes leading to their incorporation as magma globules in the host granitoid.