Transformation of Fe–Ti gabbro to coronite, eclogite and amphibolite in the Baie du Nord segment, Manicouagan Imbricate Zone, eastern Grenville Province

Fe–Ti gabbros from the Baie du Nord Segment of the Manicouagan Imbricate Zone, metamorphosed under high P–T  conditions during the Grenvillian orogeny, have been the focus of a detailed micropetrological study. Textures and mineral chemistry suggest that the mineral assemblages represent progressive stages of metamorphic transformation resulting in the formation of coronas, pseudomorphs after igneous phases (transitional) and true, granoblastic eclogites. The transitional and eclogitic samples also have coronas which are developed locally around igneous xenocrysts of plagioclase and olivine. The deformed margins of coronitic Fe–Ti gabbros are transformed to amphibolite and contain clinopyroxene‐bearing leucosomes with garnet poikiloblasts that are indicative of high‐ P–T  dehydration melting. Interpretation of garnet zoning and thermobarometry suggest that the highest P–T conditions are recorded by coronas around xenocrysts ( c. 720–800 °C at 14–17 kbar) and garnet–clinopyroxene cores in granoblastic assemblages ( c. 740–820 °C at 13–17 kbar) in the eclogitic samples. Re‐equilibration during the early stages of exhumation at high‐ T  conditions (>700 °C) affected all samples, and is evidenced by the widespread development of pargasite‐bearing plagioclase collars in the coronitic and transitional metagabbros and by widespread re‐equilibration of the eclogites giving lower P–T  estimates at grain boundaries. However, the difference in calculated pressure conditions between coronite and eclogite samples is consistent with increasing pressure (depth) from the coronites (11–13 kbar) to the eclogites (13–17 kbar). The P–T  conditions recorded by these rocks define a metamorphic field gradient which suggests high heat flow through the lower crust during the Grenvillian orogeny.