Formation of garnet coronas during high-P retrogression in mafic granulites of the Mesoarchaean Tasiusarsuaq terrane, southern West Greenland

The Mesoarchaean Tasiusarsuaq terrane in southern West Greenland consists of TTG gneisses, and, locally, supracrustal rocks that were metamorphosed to medium-pressure granulite facies conditions at ca. 2.8 Ga. Typical mineral assemblages in mafic granulites are clinopyroxene + orthopyroxene + plagioclase + quartz + hornblende ± garnet, and quartz + plagioclase + clinopyroxene + orthopyroxene + biotite in TTG gneisses. The peak of metamorphism has been estimated at ca. 750-800°C and 8-10 kbar, and was followed by locally extensive amphibolite-facies retrogression, most notably in a several km-wide zones at the northern margin of the terrane.